Question about 1999 Oldsmobile Alero

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Electric fuel pump for 90 cherokee won't work properly.

The pump and the relay are new. The ignition switch is good. The battery is good. Continuity from hot to ground is good on both the line and the load side of the power connection to the pump. A nightmare to get the thing started. Once it has been running, it can be shut off, and then right back on again, but only if it does not sit for more than a minute or so. I've had some good suggestions.. but haven't been able to solve the problem. Will greatly appreciate any help or advise. It's a 4.0 liter MPI. Thanx-a-bunch.

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  • 11 more comments 
  • graywolf0577 May 10, 2009

    Thanx for the tip. The pressure regulator is good. Any other suggestions???

  • graywolf0577 May 10, 2009

    Runs a little rough at idle.. but smooth as butter when you throttle it up. No black smoke at all.

  • graywolf0577 May 10, 2009

    Thanx. It'll probably be tomorrow before I have any more questions. Thanx again for the tips.

  • graywolf0577 May 10, 2009

    Forgot to mention that I changed the plugs a week or so ago, and don't remember them being wet with fuel. I do have a pressure tester, but the connectors don't fit the fuel rail. The problem seems to revolve around the fuel pump not turning on when it is suppose to. I've written a novel on all of the different things that I have tried and tested under a different posting on this web page, but I don't if that info is available to you or not. I originally posted my problem back in April under the same screen name. If you still don't mind helping, and you can't find the other posting , let me know and I will re-write everything on this one. Thanx again.

  • graywolf0577 May 10, 2009

    It's posted by graywolf0577 on April 19, under "Electric fuel pump for 1990 Cherokee...". You'll know it if you find it, like I said it's practically a short novel. There's also one solution posted by "thundergod". Like I mention in my second comment under that posting, I hope I don't offend anyone by seeking different point of view. Thanx again for your time... it's greatly appreciated.

  • graywolf0577 May 10, 2009

    I have a second posting under "grounding connection for electric fuel pump on 1990 cherokee...", but that's not the one with all the details. They are both posted under "1990 Cherokee Limited". I think that's main chat forum or whatever it's called.

  • graywolf0577 May 10, 2009

    I figured I'd save you the trouble of trying to find the original posting as you are already being kind enough to help me out. If you're still there you might want to grab a seat 'cause this kind of long. This is what I originally posted: "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 key to the "run" position, 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 it will idle to high ( between 2000-3000 rpm's ), but not all of the time. I'm pretty sure that all of the 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 find the cause of the problem. Again, it's a '90 Cherokee/ 4.0 liter/ MPI fuel injected inline-6, 5-speed manual, 4-wheel drive.
    The solution that was offered by another expert was: " A delay in fuel pump may be due to either a "lazy" relay or an insufficient ground ( fender, firewall, or pump itself ) It could be a poor connection at the 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 being on that circuit at all. Have you tried a code check? Only other thing 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. "
    I have part 2 of my novel to add to this... but I think my e-mail mght be recieving a reply... so I'll be right back.

  • graywolf0577 May 10, 2009

    Thanx. I've lost track of what info I've given you while I've been jumping back and forth between postings, so I'm going sign off for a minute or two and get my bearings. I entered a reply to your relay question on the other posting. Sorry about all of the confusion. I'm kind of a computer-dummy. Be back in a few.

  • graywolf0577 May 10, 2009

    Oh yeah... you can here the relay click after the ignition switch has been turned to "run". It clicks after about two seconds.

  • graywolf0577 May 11, 2009

    Thanx. If I remember correctly, there are only three wires going back to the pump. two colored and one black. I'm going to go and dig around in the tool box and see if I can find a test light, and then proceed with testing. It might be a little while before I sign back in. I really appreciate all of your help. I'm broke-as-a-joke and can't afford to pay someone, so your help has been a blessing. I'll post more feedback as soon as I can. Thanx again.

  • graywolf0577 May 11, 2009

    Hi again. The test light that I have is a clamp type and won't fit into the plastic wire connector. But I did get some readings with the multimeter that might be of value. On the line side of the connector there are three wires. A larger red with a black stripe, a smaller peach colored one, and a black that is the same size as the peach one. The reading for the red w/stripe to black 9.4 ohms of resistance with the circuit off, and reads a good 12.5 volts when you turn the circuit on. The reading for the smaller peach colored wire to black is 88.1 ohms of resistance with the circuit off, and 6.8 volts with the circuit on. Again... this is on the line side of the plastic connector. On the pump side of the connector there are also three wires. Purple, orange and black. All of these are the same size as the larger red with black stripe wire on the line side. On the pump side the readings are as follows: purple to black is 49.5 ohms of resistance, and orange to black is 1.1 ohm of resistance. When you plug the line side of the connector into the other connector on the pump side the wires connect as follows: red with stripe to orange. Purple to peach. And black to black. Look forward to more feed-back. Thanx again for everything.

  • graywolf0577 May 11, 2009

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

  • graywolf0577 May 11, 2009

    Thanx. I'll leave you alone for the evening... I won't be able to do anymore testing tonight anyway since it's dark outside. I'll try to post some more feed-back tomorrow. You've been a huge help.



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  • 253 Answers

Check your fuel pressure regulator. It will have a vaccuum line to it. With the truck running pull the vac line and see if fuel comes out, if so it is bad and should be replaced. Good Luck

Posted on May 09, 2009

  • 6 more comments 
  • Mike White
    Mike White May 10, 2009

    It the truck running rough, or does it blow black smoke when it starts?

  • Mike White
    Mike White May 10, 2009

    I would let it sit for a little while, pull the plugs and see if any are wet with fuel. This can cause a hard start. If you have a fuel pressure gauge, connect it and after you kill the engine watch the gauge for a rapid fall in pressure. A slow drop is normal but rapid loss of pressure means you have some type of leak. The next time it fails to start try cycling the key off/on several times before you start it to see what happens. If you have a wet plug then you have a leaking injector. Let me know if I can help.

  • Mike White
    Mike White May 10, 2009

    Any time, glad to help

  • Mike White
    Mike White May 10, 2009

    I will see if I can find your post.

  • Mike White
    Mike White May 10, 2009

    The anti drain back (foot valve ) in the pump is why I was interested in the rapid pressure loss. Also having to hold your foot on the gas to get it to start may be a sign of a sticking injector, which would leave a plug wet and cause a rough idle for a moment or two. It sounds like you have the bases covered pretty good. When it fails to start can you hear the relay click? Have someone try to start it next time it fails and see if it clicks. The PCM provides a ground to the relay to make the contacts in the relay close completing the circuit for the pump. On the fuel pump connector you should have 4 wires. 2 grounds 1 wire for the gauge and a hot for the pump.The relay should have 1 hot at all times, 1 switched hot, a ground and a PCM controled ground. The PCM will send the ground to the relay while you are cranking the ignition and after it senses the vehicle is running through ignition inputs. If you have a bad foot valve you should be able to cycle the key on/off several times to get it to start. If your PCM is having some type of failure it should show up while checking the relay ground provided by the PCM. I will try to find more info for you. Thanks, Mike.

  • Mike White
    Mike White May 10, 2009

    Ok at the fuel pump connector, there will be 2 grounds, 1 wire that feeds the pump, and 1 wire for the gauge. The wire for the gauge is os a variable resistor. It will light a test light either dim, or will make it pulse. If both grounds are good, an ohm reading of less than 1 ohm, test the 12 volt supply for the pump at the pump connector. If when the vehicle fails to start you have a full 12 volts then your issue will be with the pump, or the connection inside the tank to the pump. You can test this at the harness close to the tank if you know what color wirefeeds the pump. Be sure to test all 12 volt positive circuits with a test light, because a volt meter will not (load) a circuit enough to really test it. Let me know if any of this helps.

  • Mike White
    Mike White May 11, 2009

    Ok the large red will be the pump feed, the peach is the gauge and black is ground.. The ground shouls be less than 1 ohm. The other readings are ok. I would take a jumper from your ground and hook it to a clean spot on the frame. Hook it up and see what happens. A high resistance in a ground can do some wierd things. If you do not have any luck let me know. You can tie the jumper wire in anywhere in the harness but try to get close to the connector, and to a bolt or screw in the frame.

  • Mike White
    Mike White May 11, 2009

    you have mechanicm, glad to help



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Could I run a electric fuel pump on my 1998 Cadillac deville?

if it did not have an electric fuel before then the installation of an electric pump is a relatively easy process. If you have an electric pump already fitted but it has failed then remove it and install the new pump in its place. Take care to check all wires, fuses and relays and any pressure sensors for correct operation. Remove and blank of the opening for any mechanical pump on the engine
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Check your main fuel relay.

Fuel Supply System

PGM-FI Main Relay


This PGM-FI main relay is located behind the dashboard

lower cover. The PGM-FI main relay actually contains

two individual relays. One relay is energized whenever

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power to the fuel injectors, and power for the second

relay. The second relay is energized for 2 seconds when

the ignition is switched on, and when the engine is running.

It supplies power to the fuel pump.






Relay Testing

NOTE: If the engine starts and continues to run, the PGMFI

main relay is OK.

1. Remove the PGM-FI main relay.

2. Attach the battery positive terminal to the No. 3*

terminal and the battery negative terminal to the

No. 2* terminal of the PGM-FI main relay. Then

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No. 2 terminal of the PGM-FI main relay.

• If there is continuity, go on to step 3.

• If there is no continuity, replace the relay and




3. Attach the battery positive terminal to the No. 4 terminal

and the battery negative terminal to the No.

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that there is continuity between the No. 3 terminal

and No. 1 terminal of the PGM-FI main relay.

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• If there is continuity, the relay is OK;

If the fuel pump still does not work, go to Harness

Testing on the next page.

• If there is no continuity, replace the relay and






To IGN. 1 To BAT



A13 and B1




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