Question about 1990 Jeep Cherokee Limited

1 Answer

Electric fuel pump on 1990 cherokee, 4.0 liter won't turn on.

Approximately 260,000 miles on vehicle. The pump is new. Second one that's been installed since the 230,000 mile mark. Fuel pump relay is good. Battery is new. Vehicle runs fine once the pump comes on, but requires excessive attempts to start when attempting a cold start. The vehicle can be turned off, and then restarted as long as it does not stay turned off for more than a few minutes. The entire electrical system energizes when you turn the switch to ''run'', but the fuel pump does not turn on. During the cold start, when the pump finally does turn on, I sometimes have to hold the throttle a little open to keep it from stalling until it has been running for a minute, and other times the engine will idle to high (between 2000-3000 rpms), but not all of the time. I'm pretty sure that all electrical & vacuum connections are good, but I don't know, I'm not a mechanic, I've only checked what's easily accessible. I can fix it if I can just find out what the cause of the problem is. Any advise would be greatly appreciated. Again it's a '90 Cherokee/ 4.0 liter/ MPI fuel injected inline-6, 5-speed manual, 4-wheel drive. Thankyou.

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  • 28 more comments 
  • graywolf0577 May 10, 2009

    I've tested the continuity between the hot wires and the ground wire that run to the fuel pump on both sides of the connector, and get a good test. The ground connection that I was able to find on the firewall appears to be in good shape ( it is the flat braided type ) and is connected to the body, under the hood just below the windshield. I put a new fuel filter in "just to see" but that did not help either. I replaced the key lock cylinder because that was worn out and needed to be done anyway, and removed and tested the ignition switch ( which is a separate unit on this model ) and the switch is good. While I had all of this stuff taken apart, I connected the leads on my multimeter directly to the hot feed (red) wire on the connector that plugs into the ignition switch and connected it directly to the wire that feeds the fuel pump circuit (yellow). When set to test voltage it reads between 12.2 and 12.4 volts. When set to test current it will read 0.8 to 0.9 amps for about 2 seconds and then jumps up 1.5 to 1.6 amps and holds that reading steadily even though I can here the relay turn the circuit off. When I test the current draw on the circuit... as always when I am attempting to start it... I can here the pump energize slightly, but it will not run at full speed like it's suppose to... not until I've cranked the hell out of the engine. Again, once the pump finally turns on all of the way, the engine runs like a dream. Thanx for the last tips you gave me...do you have any other suggestions. Someone else suggested pulling the plugs and checking them for fuel saturation, but I replaced those a week or so ago and don't recall them being wet with any fuel. I've been surfing around between different points of view on this web site, I hope that doesn't offend anyone. Anyway...I look forward to any feed-back. Thanx again.

  • Anonymous May 10, 2009

    Thanx for getting back with me. The relays are identical, and one of them ( starter I believe ) did have a little bit of some half sticky half corrosion looking stuff on one of the prongs. I cleaned it as well as the receptacle with some "electric motor contact cleaner", and have tried moving the new after market relay that I have around within the relay center under the hood... but haven't had any luck. Funny thing I've noticed when I dig around the electrical system in this thing- some of the relays are Canadian ( the four that are in the relay center under the hood ), and others are made by Lucas. The new one I have was purchased at Napa. As I said before, the pressure guage that I do have won't fit the connector on the fuel rail, but I think that I might dig around the garage and see if I can find something that I can "jimmy-rig" it with... I'm pretty sure the pressure's good when the pump finally turns on... engine runs like new once the pump is humming away... although I do hear very slight fluctuations in the "humming" once I get it running. I think you just sent another reply. Be back in a few.

  • graywolf0577 May 11, 2009

    P.S. I don't know if I'm chatting with "thundergod" or "mechanicm 639" as I've been jumping back and forth between the two postings.

  • graywolf0577 May 11, 2009

    It seems that you share my same frustrations with the Haynes manual. The Chilton is frustrating too. They both have a lot of good info in some areas, but lack in others...they also seem to jump around from chapter to chapter just to trouble-shoot one thing. Anyway...I have some feed-back if your still there. I get a reading of exactly 1 ohm from the black wire on the line side of the pump when I connect it to the chassis. I can't find a way to make my pressure gauge fit the fuel rail (the gauge is an old one)... but I had an interesting question come to mind while I was messing with stuff. Should there be a slight vacuum at the fuel tank vent lines when the vehicle is running??? I'm talking about the ones that come right off the top of the tank. There are two that attach to the top of the tank (small rubber hoses) and then they splice together to a single hose of the same size which then runs to the front of the vehicle somewhere. I got it started up, and while it was running, I crawled under the tank and disconnected them and didn't feel any vacuum there. I was wondering if they were a vacuum vent or a pressure relief??? The manual mentions that if they are clogged, it could effect things. Was wondering what you thought. I looked past this possibility initially... but I'm starting to wonder if that's where the problem is. Thanx. Hope to talk soon.

  • graywolf0577 May 11, 2009

    Also forgot to mention that if I turn the ignition switch to "run", and leave it on for several minutes before I try to crank the engine over...it acts like it wants to go. The pump seems to be making the same kind of noise it would make AFTER it pressurizes the system??? I though that one of the lines might be clogged, but I have disconnected both the sending line and the return line at the pump, and still don't have any luck. That's when I got the notion to mess with the vent lines?? Also, leaving the switch on "run" before I try to start it dosen't make much sense to me, because you can here the relay open the circuit after two seconds. Talk about a brain teezer.

  • graywolf0577 May 11, 2009

    I've had a few things stolen over the years too. Simple thing like a tape measure comes up missing... and it really gets under your skin. I'm still kind of new to this stuff, so I was wondering if when you mentioned using an a/c gauge if you were talking about a compression gauge. Was also wondering if there was a way to check codes without a diagnostic tool. I had read somewhere online that you could turn the key on and off 10 or 15 times, and then count the number of flashes that that the instrument cluster gives you...but I believe that trick only works 91 and newer models and I did try it just for kicks but couldn't get anything out of it. Oh, is there anywhere else on the fuel rail other than the pressure test port that you can connect a tester. On the Chevy thing... figured they were starting to slip a little when they discontinued the 350. What the hell were they thinking!!

  • graywolf0577 May 12, 2009

    I hope the pumps not bad already. It' only been in there for 10 or 15k miles. It's a Carter I think. What-ever Napa's after market brand is. The one before that was a Bosch, and I only got 18,000 out of that one...and then the one before that was a Napa aftermarket...but I got about 50,000 out of that one. Don't know what was in it before that. I bought the vehicle used, and I used to just send it to the shop for repairs. Now it's become my personal project and at the same time it's my daily driver. Kind of frustrating. Maybe I should just pull the pump and hook it up to a battery. I was trying to avoid that...but no pain no gain...right. There might just be a ****-load of sedemintation clogging the strainer or something.

  • graywolf0577 May 12, 2009

    Sorry about all of the confusion. I think most of the info is on this posting. But some of it is on the other posting that I originally contacted you on (the one for 1999 alero)... I don't know how the heck I ended up posting stuff under that heading (I get kind of twisted around when I'm using the computer)...but some of it's on that one. I don't think I have any a/c gauges. Is it safe to connect the fuel pump wiring connector to a jumper to a battery while it's still installed in the tank??

  • graywolf0577 May 12, 2009

    The filter is brand new. Probably doesn't even have 100 miles on it. The resistors in the circuit are probably the main reason that I am frustrated with the manuals that I have. The Haynes shows a ballast resistor between the pump relay and the rest of the circuit to the pump which is also connected to the starter relay. This already confuses me. Then it shows several capacitors on that circuit as well...but doesn't tell where any of them are located... just that they are there. It also shows that the pump is connected to ground,,,but doesn't specify where that wire is connected to the chassis. I'd trace the wire, but it disappears into the frame and I have no idea where it comes out. The Chilton on the other hand doesn't show any resistors or any capacitors anywhere on that circuit, and like the Haynes, shows a ground connection, but doesn't specify the location. Talk about an electrical nightmare. If I get this one figured out, I think I'll have it made. By the way...you have the patients of a saint. I really do appreciate all of your help with this. A shop would probably have made a small fortune on me by now.

  • graywolf0577 May 12, 2009

    Thanx for the feed-back. I'll keep pluggin away at it. Hopefully have some more feed-back tomorrow night sometime. Good-luck hunt'n.

  • graywolf0577 May 13, 2009

    I agree. I had a bunch of stuff come up, and wasn't able to work on it today like I had hoped. I should be able to get back under the hood tomorrow. I'm going to check everything that you mentioned above. I'll get back with you when I have actually made some progress. I think that I have spent to much time jumping back and forth instead of getting "systematic" with my approach. It' s been a good learning experience for me though, and that's always a good thing. I sincerely appreciate all of your time and effort with this. Like I said...I've learned a lot. I'll post a comment when I actually know more. Until then, take care...and thanks again for everything!!!

  • graywolf0577 May 14, 2009

    Have one quick question tonight if you're there. What should the resistance value (ohms) of the ballast resistor that the pump circuit uses be? My meter reads 1 ohm from prong to prong. Also... I checked the idle air valve. It appeared to be in good running order. I also jumped the pump straight off of a battery and it worked right away. I feel like we are getting closer to the problem...especially since messing with that resistor. If I by-pass the resistor and just splice those two wires together...it seems to start more easily... and the pump sounded like it ate it's "Wheaty's" for breakfast. There is still some hesitation ( the pump ) if it sits off for more than a few seconds...but I think we are getting warmer. I'm going to try and borrow a pressure tester tomorrow.

  • graywolf0577 May 14, 2009

    I actually just pulled the resistor. It's 1.1 ohms ( stamped right on the front of the damn thing ) Now I feel feel stupid. I guess the resistor is good. The connections were in horrible shape...but I cleaned those up. Went through a whole can of electric contact cleaner today just looking around for "stuff ". ( 260,000miles worth of grease, dust dirt, vegetation, and a few creepy-crawly's ). That by-pass wire that you're talking about is the first thing I will start with tomorrow. Sure wish the manual's contained a "blue-print" along with the diagrams.

  • graywolf0577 May 14, 2009

    I'm starting to think that by the end of this one...this posting will be a fairly relevant "manual" on '90 Cherokee trouble-shooting and repair. The next person who has this problem with this vehicle probably won't even have to post the question. They can just refer to this posting and have an entire encyclopedia right in front of them.

  • graywolf0577 May 15, 2009

    I think they design stuff this way on purpose so that they can continue to make money from you even after the vehicle has been paid for. Half of the time when I look something up in the Haynes or the Chilton...they recommend that you have "this part" tested at a " dealer approved " service department. Do you know anything about the "EGR valve solenoid". I'm starting to think that if that's not the main cause of the problem it is at least contributing.

  • graywolf0577 May 15, 2009

    10-4. I was just curious. According to the Haynes wiring diagram the solenoid that controls it is connected to the pump electrical circuit and when I was messing with that ballast resistor I discovered the solenoid (it's located just above the ballast resistor). According to the diagram it's connected "electrically" between the pump relay and the ECU. They refer to it as the "EGR evaporator canister solenoid". Something else I discovered...the starter relay is not identical to the pump relay as I had previously thought. It's a larger metallic type of devise that looks kind of like a spider or an octopus when everything's connected to it. I found some horribly corroded connections at the prongs...cleaned everything up...no luck.

  • graywolf0577 May 16, 2009

    F'd up Jeep driver's Log: Star Date 541986.7358994: I'll try to find a way to "jimmy-rig" my pressure tester onto the fuel rail tomorrow. The tester is probably 50 years old and does not fit the pressure test port on my vehicle. The test port is a threaded "male" end. The tester I have has the same type of connector that you would find on an air compressor hose...but this seems to be the info we need so I'll try to "rig" something. To answer your question...the ballast resistor and the EGR evaporator canister solenoid on mine are located right next to the plastic air filter box on the driver side under the hood, and the starter relay ( at least that's what I think it is ) is located just between the battery and the relay/power distrodution center on the passenger side under the hood. It's mounted on a metal harness in front of the other 4 smaller plastic relays...the ones that are just in front of the pressurized coolant bottle. You have to remove a small plastic cover to get to them. If this pump's bad... Napa just lost my business. Is there a particular brand that you recommend??

  • graywolf0577 May 16, 2009

    Thanx. Hopefully I'll have a pressure reading to post sometime tomorrow.

  • graywolf0577 May 19, 2009

    I know...I know....pressure. I'm still working on that. Just had a quick thought though. I was doing a little bit of research and found something that seems to happen with these things "historically". What about the "Crank Position Sensor"?? Was just wondering what you thought.

  • graywolf0577 May 23, 2009

    Still no luck...but I haven't been able to get a pressure reading. I'm still working on finding a "loaner" that will fit the fuel rail. I've started to question the possibility of wiring ( if I hook my meter up to the connector that feeds the pump...I get 11.5 volts with the starter cranking.) I'm not an automotive electrical expert, but I know the starter pulls a lot of "juice" when it's cranking, and I'm guessing that if the pump still gets 11.5v even when the starter is cranking... the connections up until that point have to be good. I haven't brought the sledge hammer out yet...but I do have a 7/8 wrench that has come close to doing more than just turning nuts and bolts.

  • graywolf0577 May 23, 2009

    I'm still going to try and get a pressure reading before I take anything else apart. But I have a strange feeling that it will be within the specified range ( 31-39 psi ) if I'm not mistaken. I keep having "visions" of pulling the pump and finding either a bad connection inside the tank, or an astronomical amount of "****" floating around in there. I've ruled out "running dry syndrome"...I rarely run it at less than 3/4 of a tank...( use good Shell gas too ).

  • graywolf0577 May 23, 2009

    10-4. If and when I end up pulling the pump, ( and I do think that will answer a few questions ) I'll let you know what I find. This thing is getting ready to become a "tear down & rebuild" project anyway. I'm trying to squeeze as much out of it as I can until I can afford something a little newer. When it does become a project...there are going to be some serious changes ( mainly in the electrical & the cooling system ). I still think the engine has a lot of life left in it...but lots of other stuff is getting old and tired...it's gone up-over-under-&-through a lot of things that I probably had no business trying to navigate...but did them anyway "just for the hell-of-it"...the paved road gets boring you know.

  • graywolf0577 May 24, 2009

    No problem. I'm surprised that the scrolling wheel hasn't fallen out of my mouse yet...Heh-Heh. I'll let you know how the over-hall goes too...but I probably won't start that for a while ( economic crisis and everything ). Just trying to keep it running for the time being. I'd swear that the thing has a personality of it's own. Up until recently...when it would get tempermental... I'd just take out into "the sticks"...romp it around for a little while...and it seemed to be happy afterwards. Ahhh...the good old days.

  • graywolf0577 May 24, 2009

    That is interesting. I wonder if , when they were designing the 4, they did the same thing that GM did with the 4.3 liter...( I'm pretty sure the GM 4.3 was just a 350 small block with the rear end chopped off of it.) If I'm interpreting what your saying correctly...that would mean that you could take the higher compression pistons out of the 4-banger...stick them in the 6... (assuming that you could find two sets of pistons, and didn't mind having two left-overs)...and blamo...more power?? Like I said, I'm not a mechanic...I understand quite-a-bit...but not all of it??

  • graywolf0577 May 24, 2009

    Very interesting. You lost me a little bit on the detonation part...( I'm guessing you mean pre-detonation due to "over-compression", kind of a dieseling effect???). It will be a little while before I get to make it a full time project...but I'll take any info and stick it in the old computer for future reference. I wonder if the people that run this web-page are going to kick me off of it for using up to much space. Hope not!! It's kind of become a nice little chat forum. Talk to ya later!!

  • graywolf0577 Jun 18, 2009

    Finally just sent it to the shop. Sure enough it was the pump. Still wondering why it is burning them up in 20,000 mile increments. If this this one goes...maybe I'll try OEM instead of after-market??? I know that on some vehicles...you just had to replace stuff with OEM if you want any kind of "life" out of the part. The guys that I sent it to are old-school and very trustworthy. They spent close to a week looking for possible causes for the problem. Couldn't find anything except for a burned out pump. The saga continues....!!!

  • graywolf0577 Jun 18, 2009

    Thanx, When I finally get around to over-hauling the whole vehicle I'm definitely going to pursue your idea of the external pump. Seems to be the only area of the vehicle that has given me a head-ache. Well that and the damn pressurized coolant recovery bottle ( working on bottle #2 & cap #3 in that department ). As far as engine mods go...wasn't planning on doing a whole lot more than a balance-&-blueprint on the re-build. I kind of like it the way it is stock. It aint a hot-rod by any means...but it serves a purpose and does what it's suppose to ( crawl up-&-down stuff, & "clings" to a slick road during the winter months ). Might tweek the suspension a little...but, like I said before, it's going to be awhile before I get around to all of that. In the mean time, thanx for all of the help and advise. When I finally get around to my "project", I'll look you up on this site and let you know how it goes. Until then...take care, and thanx again!!!

  • graywolf0577 Jun 18, 2009

    Ah lawyers...I put them in the same category as politicians, corporate bankers, tapeworms, & snakes and other reptiles. Sounds like your ex-business partner should be in that category too. I hope everything works out OK for you. Sometimes things happen for a reason. ( Of course I do have trouble taking my own advise sometimes...I'll hear about someone going through hard times, tell 'em to keep their head up...but when sh#t hits the fan for me, my attitude becomes F*** the world...notice the "F" is capitalized ). Human nature I suppose. Anyway...I hope everything works out for you. I'm sure it will. Greedy 2-faced people that are out for a free "quick-buck"usually tend to get sloppy (because their lazy) and end up chopping their own thief'n hands off.

  • graywolf0577 Jun 19, 2009

    Hope my last comment didn't rub anyone the wrong way. Started to wonder when you didn't post back. You've probably already thought of this...but have you thought about doing a google search for legal info. There are usually government web sites that provide all of the legal mumbo-jumbo a guy could ever care to read and they're free. Just a thought.

  • graywolf0577 Jun 19, 2009

    10-4. Sounds like a mess. I hope everything works out. I'll "drop a line" when I start my "project". Good luck with everything!!!

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  • Jeep Master
  • 6,982 Answers

A delay in fuel pump may be due to either a "lazy" relay or an insufficient ground (fender, firewall, or pump itself) It could also be a poor connection at ignition switch. However I took a look at the wiring diagram I have and it seems that there are several items connected to the power supply for the pump, which I see no real reason for even being on that circut at all. Have you tried a code check?
Only thing other that I can think of would be the anti-drainback valve in the pump, but the pump should come on and re pressurize the system, not fail to run, even if the valve was bad. To find your problem, you are going to have to do a bunch of testing, till you get an idea what is happening. Just don't assume anything is good till it can be proven to be good.
I know I have not "cured your problem, but I hope I've given you enough to go on to begin testing.

Posted on Apr 19, 2009

  • 27 more comments 
  • Richard Scordino May 10, 2009

    I believe that the fuel pump has a resistor in the line somewhere...this may be the reason for the voltage change. I am wondering what condition the contact points in the relay look like. If they aren't clean, it is possible that they could be causing a voltage drop till they burn themselves clean. (I'm reaching a bit here but a wierd problem usually has a wierd solution) Also, have you checked the pressure regulator to see what it's doing? (also be interesting to see what actual fuel pressures are at any point in all this) I'm going to check on a few things and get back to you.

  • Richard Scordino May 10, 2009

    OK...don't know if you tried this already, but it appears that the starter relay and the fuel pump relay are identical. Try switching them just to see if anything changes.

  • Richard Scordino May 11, 2009

    looked at diagram to see if there is a resistor bypass to "kick" the pump when starting. that's why pressures through cycle are important. Only diagram I have for jeep is haynes it's worthless...shows three different systems and does not differentiate between two of them (to save paper?) One part shows system going through resistor relays, one shows pump running off of starter relay and other one looks like it goes through the ecm??? Glad It's not mine or hammers and window glass may meet soon!!!
    Anyhow, pressures may tell you a bit more about what's going on.


  • Richard Scordino May 11, 2009

    Following along with yth vacuum idea, try removing the fill cap. It may set a code if you run it that way but you will know what the code is and not be upset.
    I actually use my old a/c gauge set to read rail pressure it fits on there fine and pressure is pressure!
    Also, have you tried running an external ground wire there from the battery? That would eliminate any possibility of bad connection along the way. (If it was my vehicle, I likely would have run a new hot wire, resistor and ground with a toggle on the dash and a mercury switch somewhere to shut it down in a rollover. But, I'm a bit crazy, so don't do that!)
    Haynes is likely the worst manual I have ever used...I once had an assortment of the big chilton, motors and mitchell manuals...All stolen along with a personal "source book" I had compiled over the years. Aside from not having a torch and welder, I probably miss those books more than anything!


  • Richard Scordino May 11, 2009

    Messages got crossed in the "mail"...system is supposed to remain pressurized. That's why pressure test is important. I am also wondering if you may just have a defective pump. My general rule is that a new pump (or any other part) is good when it is working...not because I just took it out of the box. Quality control is abysmal (saw that coming when chevy stopped numbering connecting rods because the guys assembling the engines couldn't read the #'s !!! And, it's gone downhill from there.

  • Richard Scordino May 12, 2009

    This is starting to look like a novel!!! Somehow I sort of assumed you did all that already. Don't hook pump up to battery and run it "dry" even if it's good it won't be anymore. Also I don't remember you mentioning about other pumps...could be that if there is a resistor before the pump, it has changed value and is burning up motor.??? I'll re-read everything later but don't remember you saying pump was new? (dosen't matter now anyway)

  • Richard Scordino May 12, 2009

    A/c (air conditioning gauges) Self-diagnostics supposedly began in 91. ou turn the key on and off three times, leave it on third time and check engine light will flash #s in pairs: two flashes =#2 so two then one flash is twenty one then a pause and next #.Don't think fuel pump is in code library anyhow. (more geared towards sensors) If you drop the tank, look in there and make sure it's clean. Again I'd have to read this over but you did change filter???
    Once they took the nickel out of the block and heads, then made the heads lighter, they were getting unreliable. Ran a few 283's (low 12 seconds and a couple of 10 second 350's in a '57. Really miss that car!


  • Richard Scordino May 12, 2009

    First problem...you are reading the diagram correctly ((It's made for idiots) The "capacitors" are color changes and splices in the wire. I believe that the diagram is either showing two optional systems, What would make sense would be a full power bypass to the pump on startup then routed through the resistor. The splices bother me though...every one is a potential voltage drop or place where corrosion can breakdown the connection. From what I see, they serve no purpose. As far as ground goes I may have mentioned that on mine, because of all the problems I've seen stemming from poor factory grounding, I have two 10 gauge block to battery grounds and have "bonded" entire system (all fenders chassis firewall and dash ) with one continious single ground wire.And "00" welding cable from battery to starter. A ground is a ground which is why I mentioned connecting a direcrt ground wire from battery to pump wire.That way there is no loss of integrity.This is one of those cars that after everyone went home, I'd go back after dinner, lock all the doors crank up some cream or hendrix and go at it (after my guys tore their hair out all day) I'd go home when it was fixed, and, no extra labor was ever on a bill to customer.
    Doing this here is more difficult...i can't see hear or touch anything and have to visualize what you have and hope I get good info back.
    What i see now is a history of pumps failing so the one that's there is suspect. Power is also an issue, but you haven't run out of places to check (yet) All those "capacitors" are suspect voltage drop sources.


  • Richard Scordino May 12, 2009

    Safe to jump pump but if it uses a resistor, you can't run it long or it will burn out. And you still won't get pressure info that's important. It can run, but if its putting out twenty instead of fifty you won't know it.(same about anti-drainback.)

  • Richard Scordino May 12, 2009

    I'm gone for tonight...got to wake up at 4am and go shoot a turkey.
    (the late worm dosen't get eaten by the early bird?)


  • Richard Scordino May 12, 2009

    With all the attention on the fuel pump, I re-read your original post and noticed something...you mentioned that you need to run with your foot on the throttle after starting and that idle is too high...Have you checked the idle control valve (next to the throttle position sensor ) to make sure its clean and functional? If it's hanging up, it will mess with air volume on startup (change mixture). which you are then compensating for with your foot. If you remove it, don't loose the "o" ring seal and don't turn the valve end when cleaning. check the passageway to it as well & make sure that's clean too.Do same for throttle plate to make sure it seals when closed. Just a possibility, but we may be working on the wrong end of the car.

  • Richard Scordino May 12, 2009

    I just reviewed all the stuff you posted under Alero...It seems that we all are going in the same direction. Two things that come to mind though are what I just posted about the idle valve and that you really need to know what kind of pressure and if drainback valve on the pump you have are good. Otherwise we will all be chasing our tails forever and when finished, will have written a new novel (Gone With the Fuel Pump?)

  • Richard Scordino May 14, 2009

    This is the first time I've ever had to use the "scroll" feature on an answer!! I don't know what the resistance is supposed to be. Don't run pump on straight 12v long...it could burn out. The way I decipher the great diagram I have, I believe that the resistor is supposed to be bypassed through a relay for the starter motor, then, in "run" power goes through the resistor.(that would make sense) I've actually used a similar layout when building ignition systems. It doesn't need to cut down voltage by much, just take the "edge" off it. Like a Chrysler ballast resistor for ignition. I'm wondering if everything on the run side on yours is OK and the bypass wire from the starter relay isn't. That leaves one remaining question...what is causing the pumps to fail early?

  • Richard Scordino May 14, 2009

    For a really long time now I've wanted to write a manual containing real stuff...especially locations of items, and everything you need to know about them. Unless you work in a dealership (one kind of car all day long) you never get to or have time to find out all that stuff. I've had cars that had things under the hood that I had no clue what they were..they never failed, and never had time to find out what they were.
    And, I was in the business and was fairly competent (even had ase certs!) In my shop, we worked on everything, unless I didn't like the car...Then I wouldn't let it in the parking lot! (especially VW beetles and carman gias) Otherwise, worked on armored trucks to top fuel.


  • Richard Scordino May 14, 2009

    Only an expert on Jeep fuel system....Aftert his, I think when my pump goes, I'm getting an external pump and regulator with an anti-drainback valve and wiring it my way...I'd really like to meet the people who design this stuff!!!

  • Richard Scordino May 15, 2009

    You have an egr valve on yours? Haven't seen one on many 4.0 engines. I know they did use them. egr usually has more to do with how it runs after it starts...especially if it's blocked. Are you sure you have one? After all, you have to be making eg (exhaust gas) to r (recirculate) it. If the valve was wide open and unblocked it could have some effect, but don't go that way...it makes no sense.

  • Richard Scordino May 16, 2009

    You just lost me...I don't have a good diagram (we know that) and I use my jeep for a reference vehicle a lot. Since I haven't had your exact problem I never had to locate the ballast resistor, (only resistor I see on mine is on the driver fender and I don't exactly know what that one is for, except that it's good) and do not have an egr on mine. Where are you finding this stuff?
    When tracing wires on computer stuff, one thing I use that I did not mention. I attach a semi-used 1.5v (one that reads 1.4 or 1.3v) battery to the wire I can see, and disconnect the vehicle battery...then the only hot wire is the one I'm working on. and the voltage will not damage anything.I'm starting to think that the pump is just not right. Without pressure tests we won't know that.



  • Richard Scordino May 16, 2009

    Believe it or not the pumps rrom the dealer are supposed to be better than any on the aftermarket. personally, I am likely to do what I said before and if mine goes bad I'll probably put an MSD unit in there with a back flow valve added. (external). You can probably use any pressure gauge that reads over eighty pounds. The rail fitting is exactly the same as on an ac unit.(why I use my old ac gauge on there)

  • Richard Scordino May 19, 2009

    Crank and cam sensors are part of the ignition system and to the best of my knowledge, do not control fuel pump operation in any way
    If cps was even partially failed, generally the symptom of the onset of failure would be unexplained stalling, then being able to re-start after a short cool down, followed shortly thereafter by a stall and no start (forever) condition. I'm pretty much convinced that either the system is not sending enough power on start up (to the pump) or that the pump itself is lazy, and not getting up to speed right away.
    When dealing with electrical components it amazes me how they can develop new and exciting ways of failing. But, with proper testing (fuel gauge on the rail and meter on the pump connection) you can run aq good test to determine what is doing what, and when. Just saw some fuel gauges in a Summit race catalog that were not too expensive. you would need one hose from an a/c gauge set or as I said, anything with matching thread size.


  • Richard Scordino May 22, 2009

    Well? Is it fixed or have you beaten it to death with a sledge hammer??? (I still mentally work out problems with cars that are long ago in the scrapyard...thankfully there were only a few of them)

  • Richard Scordino May 23, 2009

    I will feel guilty if I get you to spend $200 on a new pump if it doesn't work, but I think after what is known so far, you could do that. Only question is the "why" only because I don't consider it fixed unless the cause is known and measures are taken to prevent a repeat failure. (I'd even consider putting a capacitor or resistor on the power side of the pump, to prevent "spikes") 11.5 is fine and I'll bet you get the same reading @ the battery when cranking.. Check the insides of the tank for any junk as well. You can also add an additional ground near the tank and tie the original harness wire to it. Unless the ground is open at some point during key turning. Unless there is something huge we both missed ,(I seriously doubt it) I don't see why it would not work.
    Don't know what you do for a living, but sometimes you need to take a "leap of faith".


  • Richard Scordino May 23, 2009

    Actually I'd rather see a ton of junk in the tank! at least it would give you a "why". Haven't used Shell in a really long time...Used to see a crusty residue on customers plugs that looked like a yellow shell around the electrodes and on the ground strap. Also mostly driving stuff with at least semi-hot rodded engines (even the last one, an old dodge dart with a 321 (non stock 318) 4bbl with a ton of suspension stuff done to it). Always ran the best Sunoco stuff available with something else added. (still miss the old 260). Lately I try to find anything with the lowest amount of ethanol and add acetone. Even my last car before Jeeps old chrysler fifth ave had an r/v cam set four degrees over, and suspension tricks.(just can't stop playing!
    Anyhow...I think you are there...regardless of pressures. unless as I said, we missed something, but I really doubt it!!!



  • Richard Scordino May 23, 2009

    Yup...Just got my nephew a deal on a 98 for $1700...he's had me out there putting in a new sound system, gps, radar detector,complete synthetic changeover. and now, since it's a little 4cyl, He is asking about engine mods to make it go faster...they don't really make much stuff for that but now he's thinking about a turbocharger (thank god they are really expensive,,,maybe he will change his mind!!!) he took it offroad the other day (right after waxing it) just to get it muddy. and cut down a tire it the same hole I split a trans line a week before in mine. Except for the smaller engine, his makes me a bit jealous!!! But it's his money and getting nearly a 4.0 in his first semester in college, how can I tell him no?
    .Anyhow, let me know what goes on with it...need to learn something, especially since this has far exceeded the longest post I have ever went with in over 1800 ansawers I've given...Who Knew???

  • Richard Scordino May 24, 2009

    Just noticed something interesting if you are going to rebuild. the 4.0 has the same bore size as the four cyl . BUT the 6 ahs 8something to 1 compression and the 4 has nine. If the wristpins are at the same height, you can get some free horsies from that. (well, not free, you need to get the pistons)

  • Richard Scordino May 24, 2009

    Both have a 3.88" bore the 4cylo has 9:2:1 compression the 6 has 8:8:1. that's less but the 6 has a longer stroke (a bit more torque.) I'd have to check two things...rod journal diameter and rod length. also the actual location of the wrist pin in the piston In an ideal situation you could use the entire piston/rod assembly (Id need to get out my formulas to find out what that would make) But yes compression is horsepower (why there were never less than 11:1 pistons in my race engines.) Only thing of concern besides fit would be detonation. (I could not run a race engine on pump gas even the winter if I needed to move it out of the shop without it running on even without it being really warm.) with fuel quality somewhat more like good puppy pee, I wonder if it would cause a problem. (though the 6 has no problems) Next week I just may call the guys i used to deal with at manley and childs & albert and see what they think.

  • Richard Scordino May 24, 2009

    Funny...was just thinking the same thing...must have gone to different schools together!

  • Richard Scordino Jun 18, 2009

    Pump??? Pretty sure I mentioned that a bunch of times during this whole thing. Only thing missing was a "lock" on the diagnosis via some pressure readings. Chances are that with all the testing and cleaning up you have done, you have done a lot to prevent premature failure of the new unit...and if you are using OEM as a replacement perhaps you will have a far longer service life than you have been getting before. One thing though is try not to run below 1/4 tank...pumps need fuel around them to stay cool. (why I mentioned that I would rather modify the system to use an external pump and check valve...Mercedes did that for years and never had this kind of problem.). Funny that you posted today...was wondering how it turned out yesterday!!!
    PS looked into piston and other performance mods to jeeps: turns out that cylinder walls are too thin to do anything meaningful there and only stuff available is expensive with no real dyno results to back up claims.Jeeps sure ain't chevies!!! Good luck with it!!!!


  • Richard Scordino Jun 18, 2009

    Performance mods werent only for you...I can't stand driving anything that isn't somehow faster than it should be...Or for my nephew, who is now "stuck" with a four banger that runs perfectly but can't get up a long grade without dropping into a lower gear.
    I hope to be here for a while but may wind up homeless soon...ex business partner is trying to take house away... long story but boils down to him being greedy and cheap, screwing me around on a verbal contract we had. Ran me out of money and I can't get a lawyer to help without funds...Wonder why no old lawyers don't offer help like we do on this site...sure would be nice!!!


  • Richard Scordino Jun 19, 2009

    I don't know if you offended anyone but if you did, I hope it was a lawyer. I'm just so talked out on the subject that I don't have word for it anymore. Here's what it is: Several years ago I went into partnership with a friend and bought a bank foreclosure house (108 yrs old). He contributed about 50K for materials, I put in over 145K in labor (over 10,000hours. When nearly completed on the inside, he refused to do any work on the outside and completely cut off funding...agreement was that I live here forever and we start another house when this one was done. In January I learned that he not only cut off my funds but had not paid taxes for two years (nearly three. He is demanding that I pay him rent and claiming I am a "squatter" and is attempting to evict me (though I have papers showing I am an equal partner in LLC formed for the house.)
    I've been on every website I could think of and have talked to so many lawyers that I could populate a small town with them.Same answer from all..."you have a great case but I can't represent you because you don't have any money" (all want at least 3K to even begin.) I've offered all to pay on back end as contingency. Truth is I don't even want the money anything I get I'll pay back taxes on and put the remainder into marketing an invention I have used in deer hunting (something I dreamed up back in 89 and have pulled bucks out of impossible places with ever since. (websitehttp://www.x17deerslayer.com/test) we put up website but haven't advertised because the original backer pulled out at the last minute and we missed all ad deadlines. I don't want to sound crazy but it should produce at least 30mil in sales if done correctly (that's if we can sell to 1% of deer hunters in the US.) With all this stuff going on I am about to loose my mind so I do the fix ya thing to keep my sanity. I think I may have a backer, but all he want's to do is talk and I haven't seen any financing yet. My nephew thinks he is either trying to steal the thing or he is a "spy" working for my "friend" to keep tabs on me. I spent my entire life helping people and it is really sad that now it's like I'm alone in a field with really big rocks falling and no one is helping. Even the guy who backed out on me last year came away a winner...I built three rooms repaired all the plumbing and re-wired (including 200amp service panel) nearly every room to bring them to national code, in his daughters house where Lincoln's wife used to go to talk to ghosts (documented, in Moravia N.Y.) That dosen't include the windows I removed and doorways I built etc, And I spent the entire summer there overseeing an 80K grant renovation to the house exterior. I did this free!!! In New York City they would call me a ":shmuck" and perhaps I am. I can't say more here...I likely said more than I should but I'm at fishnhunt@hotmail.com if you need me for anything.


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