Question about 1996 GMC Sierra

2 Answers

After becoming harder to start during the last 6-7 months my truck seemed to be running out of gas andthen would not start again.

The fuel pump has been getting increasingly louder, especially when 1/2 tank or lower, but not consistently. Now that it quit, I can't hear it at all. I checked the relay, using a known working relay to replace it, no help. There is no fuse listed anywhere in the vehicle owner's manual for a fuel pump or anything relting to a fuel delivery system. I checked the schraeder valve at the throttle body and there is no pressure. I loosened the fuel filter and there seems to be good flow at that point and I don't know where I can check the electrical power (at the pump?) in order to ensure that the pump is getting power at the tank. I have gotten mixed reactions on replacing the pump, either by dropping the tank or by removing the 8 bolts for the bed and sliding it back, any comments on that?

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  • Steven Cox
    Steven Cox Dec 26, 2013

    I must apologize a bit as this is my first foray into this method of problem solving and I have actually made two separate problems in this forum, thinking that the first didn't go thru.AsI now have responses to both i don't now how to consolidate them but since this response seems to be nearer to the core, I'll try to make a correction and provide some further info as several of you seem much more knowledgeable on this subject than myself. Not that it will make a huge difference but apparently I was a bit hurried and the truck is actually a 1999 GMC Sierra 4X4 with 5.3. Even more importantly I think might be the sequence of vents that occurred prior to this particular engine failure. I have been experiencing several electrical issues almost as if I have an electrical gremlin that has taken up residence in the past year or so. Taken individually and over several months time, they seem to be small nuisance items, but it may (or may not) be relevant. It started with sveral of the dash lights going out in the center section of the dash in the VAC and CD-FM stereo area. Within about a 3-month period nearly all of the small indicator lights went out, and the CD player portion of the stereo quit working (though you can still hear it spinning even when the radio is turned down). Recently the radio started losing power intermittently, most often when you are driving down the highway and signal for a lane change or possibly flash the High-beams off/on. ithink once it even went off when I moved the driver's window up or down. The fuse went out for the cigarette lighter, and i replaced the fuse and just stopped using the lighter for that purpose, instead using it only for power for my GPS and/or cell phone. Once the A/C lit up and started cooling without being toughed (the push-button switch) and it wouldn't even shut off when the on/off button was pushed. Occasionally my keyless entry will stop working (Both remotes) and that may last for a couple hours or all day. When I reprogram both remotes later then it will start working again. I've always used an Interstate battery with dual terminals simply because the side terminals are too difficult to hook jumper cables to so I use the normally unused top terminals to give jump-starts to others with. The last person I gave a jump to failed to tell me that he had a diesel and that he only had one of the two necessary batteries in his vehicle. After failing to jump his vehicle and nearly running my own battery dead,i ended up having to replace my alternator and 1-year old battery (luckily under warranty). Now to the current problem; last spring the heat quit working but as it was already getting warmer I decided (of course) to wait until a "better" time to correct that. I knew that wasn't an electrical problem so I checked for a heater control valve and learned that between 99 and 2000 a change was made and the HCV was no longer used. The hose going into the heater core was hot and the hose coming out was cold, so I decided that the heater core was most likely clogged up. I went and picked up one of those back flush kits that basically includes a T fitting that goes in one of the coolant lines and you use it to flush out your cooling system with a garden hose. I decided to isolate the heater core and flush it separately rather than have all that sludge get pumped through the radiator before draining out. I installed the T and then clamped off the line on the engine side of the "cool" line. As I was preparing to remove the other (hot) hose from the heater core to attach an extra piece of hose I had purchased, the plastic fitting at the heater dore simply crumbled and fell apart before I could even get a grip on the clampt to loosen it. I had already clamped that line near the engine but quite a bit of nasty coolant ran down all over the side of the engine. I went ahead and just disconnected one side of the T from the heater core and pulled the other line up and cutthe end off with the small bit of the connector in it and simply bypassed the heater core. Now was that wrong? Since the HCV is no longer there, and the hot water is being routed to the heater core using some type of sensor at or near the thermostat, did that mess things up? Anyway I took a hose and added some water to the overflow bottle to make up for what was lost, rinsed off the side of the engine where the coolant had spilled and was cooking and smellng terrible, then proceeded to the parts house to get another connector. I drove about 17 miles total, mostly at 60 mph except for a couple sections at about 35. As I was going down a slight hill after leaving a stop light the engine started to falter as if it was running out of gas. I turned into the parts store and had to go up a small hill and it wouldn't go, just bogging down when you press on the pedal but idling roughly if you let up. I cut it off and let it sit for a few minutes, then started up and it finally made it into a parking space but even in neutral or drive it didn't want to take any gas. So I cut it off andwent in to get the parts. I saw a sign on the door that they would use a scan tool for free to check for codes so i asked the counter person to check it since the Check Engine light came on right as I was shutting it down. The scanner showed a MAP Sensor code as well as a O2 (Bank One, Sensor One) code and i realize I should have written them down but I didn't) and cleared the codes. I crankedthe truck back up, after several spins and it seemed to be OK as I pulled out into traffic then went back up the hill to turn onto the highway and head home. just before I got to the light it started balking again as if it was going to shut off and I let up on the throttle and coasted hoping it would clear up but it finally stalled and I made it to the curb and that was it. And the Check Engine light came back on also. I called back to the parts store and spoke with the nost experienced of those folks and he asked if the truck was getting fuel, which I said it didn't seem like it but I had no way to know for sure. he asked if I had tried disconnecting the battery and waiting a few minutes to reconnect it. I asked him if that would make a difference just resetting the computer and he said it might. So I tried that but the only result was that my clock is not right and my radio stations are all gone. :-) Thinking that my fuel pump had finally quit (it had been getting harder to start for a couple months) I walked back to the parts store and paid the $$$ for a new pump, then more $$$ for my roadside service to tow it back home. A friend came over to get underneath to see if he could hear the fuel pump come on and he said he heard it start and slosh the fuel around for a few seconds, then cut off. I was of course unaware that it was supposed to only run for a few seconds, but since I had nearly run the battery dead I thought that's why it wouldn't keep running, but it still wouldn't start. It would crank like crazy but no start. And it seemed like we tried it again a dozen times, turn the key off, wait a couple minutes, and turn the key on but the pump never did come on again. Now it's sitting with the battery charger on it to try again tomorrow. But i'm not completely convinced that the pump is the only problem, or how to verify that it is getting a constant power supply. I've got a multi-meter but the probes are too large to fit into the holes where the relay goes. It's been a couple years since the Check Engine light has come on at any time other than start up when they All light up as a bulb check I guess, and that time I had hurried too much at the gas station and hadn't tightened the gas cap down, but nothing has triggered the light before or after that until now. Could the coolant spilling all over the engine (where that O2 sensor is by the way) cause this? I just don't want to put a new pump in if it's not a correction for the problem, or do I need to put a new MAP sensor and O2 sensor in first (or not at all). I guess the biggest question is, could the bypassing of the heater core have caused all (or part) of this? Sorry for the long story but I didn't want to miss something that I might not consider important but a professional would. HELP??? P.S. Merry Christmas!

  • george parkes Dec 29, 2013

    The plastic line valve you speak of is the evap test port,usually a very small vacuum,that's not the fuel .Should be on the metal fuel rail that feeds the injectors.If the pump was making noise and then quit I'm sure it needs replaced.

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2 Answers

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  • GMC Master
  • 975 Answers

Yep,check for power at the pump,the pump power will only run for about 3 seconds when you turn the key on,will also be "hot" while the starter is running.If you just "bump" the starter it will power the pump for another 3 sec .Also don't get confused with the gauge power (think it's purple) It will be low voltage and pulsing,but,enough power to light your testlight,so don't think that one is pump power.
I never tried to move the bed,looked like alot of work,I had better luck dropping one holding strap all the way and loosening the other one to drop the tank enough to roll it in (driveshaft has to come out I think) and get the unit out without actually removing the tank,can even be done this way without being completely empty.

Posted on Dec 26, 2013

Testimonial: "Thanks, I wasn't aware of the 3-second time, but am I checking the wrong schraeder valve? I ask because it isn't attached to anything but a flimsy plastic line which doesn't appear to be capable of handling 55-62 psi of pressure. But when I depress the valve there is no pressure on it and I may be hallucinating but I swear I smell gas up there in the engine compartment! Yes I was looking at the tank and the one strap method would definitely require the drive shaft be moved as it runs right alongside the tank when it goes into the transfer case. Since I have talked about sliding the bed back I have heard a method of loosening some of the bolts and removing the others then jacking up the front of the bed and propping it up with a 4 x 4 while you change the pump. Decisions, decisions... Thanks for your help!!!"

  • 1 more comment 
  • montehammons Dec 26, 2013

    That is a lot of gremlins, gmc style. How hard is it to change the heater core? A few times they were smart and made it easily replaced. Other times, the dash has to be removed . Kinda salty, but merry christmas back to you.

  • montehammons Dec 26, 2013

    Sorry for intruding, George. Excellent answer, good tidings to you also.

  • Steven Cox
    Steven Cox Dec 26, 2013

    Yep, it's a B**** and just like anything else it's easier to remove everything from around it rather than fight with it. Once you pull the glove box you can see the space you have to work with. If I had a space and the right tools the right thing to do would be to pull the dash and replace all the lights with LEDs and replace the radio too. I actually consider myself lucky as the truck is almost 15 years old and all the scheduled maint has been done (tranny flushes, coolant flushes, brake flushes etc). Aside from the alternator/battery replacement (which was my fault for being a good samaratin) I've only had to replace the starter and the rest has just been regular maintenance.

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  • GMC Master
  • 5,317 Answers

Yes, I've heard of people taking the bed off to do it. If it's only those 8 bolts and slide the bed back, sounds like a good option. Quite a bit of work dropping the tank, plus there's not a lot of room getting the filler hose off, and your hand up there to disconnect the fuel lines and electrical connector, if they are on top of the tank. With the bed out of the way, all you have to do is access the pump through the top of the tank. Check it out and see which works best for you.

Posted on Dec 26, 2013

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SOURCE: 1997 GMC K1500 4x4 5.7 ex.cab SFI injection system

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SOURCE: My 1994 suburban engine stops. No fuel, no MIL light.

I checked all of the fuseable links and they were all good. Next I decided to check all the power wires to the ECM and also the grounds from a wiring diagram because the Mil is controlled by the ecm and the bulb was good. The ecm is located behind the glove box. Bingo, the orange wire was only reading 3-5 volts at the ECM, but 12.5 volts after the fuseable link at the underhood fuse block (passenger side firewall). I ran a temp wire directly from after the fuseable link to the orange wire at the ecm and the ecm turned back on and the Mil or "check engine soon" light came on too. The truck started up and has never run smoother.

Note that at first the truck just stalled out and I could restart it right away with no error codes. Eventually the stalling became more frequent with longer reset times required. Once it threw a "code 54" and I thought it was fuel related as each time the gas stopped and I could still start the truck with gas poured into the TB. Ignition ok. My fuel pump turned on and ran if I tested it. I even checked the pressure regulator and the fuel filter to no avail.The orange wire that powers up the ecm is technically part or the fuel pump relay circuit as it also feeds the fuel pump relay 12.5 volts all the time. The thin orange wire from the fuse block is joined to two other thin orange wires in the large group of wires that heads to the ecm along the firewall behind the engine. I had to dig it out of the many wires to find it and remove a lot of tape. It is amazing to me that this one little orange wire could cause so much grief and be so hard to track down. I could not have afforded to take this problem to the Dealer.

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SOURCE: Truck will turn over but not start. Checked fuel

The ignition module located inside of the distributor is what generates the signal that the ECM (Engine Control Module) uses to time and fire the fuel injectors, as well as the signal to run the fuel pump and the dwell signal timing to fire the ignition coil. A faulty ignition module can cause any one of these systems to malfunction.

That does sound like a malfunction with the ignition module inside of the distributor, and you can remove the ignition module and have it tested for free at most auto part stores.

If you do purchase a new ignition module be sure that it does come with a silicone grease or a die-electric compound because it is a heat sink and the ignition module will burn up without it.

To install the new ignition module first clean out the mounting surface inside of the distributor. Then completely coat the metal contact surface under the ignition module with a thick coat the silicone grease or die-electric compound and do not leave any of the metal contact surface of the ignition module un-coated with the silicone grease or die-electric compound, and be very careful not to over-tighten the ignition module or it will be damaged.

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