Question about 1996 GMC Sierra
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?
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!!!"
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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Posted on Jan 02, 2017
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.
Posted on Mar 26, 2009
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.
Posted on Jun 22, 2010
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