We just had a new motor and transmission put in the truck a few months back. It has been doing great since then, until the other day. We were driving it, it backfired, and then the motor died. It wouldn't restart. Fuel pump was no longer getting fuel. Found that fuel relay was getting no power yet fuse to relay was getting power.Got a new relay and installed. Truck started up and then died again. now no power to relay, fuse, or coming into fuse. Fuse, relay, and battery tested, all still good, just no power going into the fuse that goes into the relay and then to the fuel pump. We can hard wire into the battery and truck will run and can be drove all day with no problems. I think the next step would be the computer, but, not sure that that would be the problem since it works with being wired directly into the battery. If I need, is there a way to test the computer? So, what do the machanics on board think it could be?
Thanks to anyone who even considers answering!
2007-06-06 20:59:00 · 11 answers · asked by live4love32 2 in Cars & Transportation ➔ Car Makes ➔ GMC
Thanks for all answers thus far.
We have tested the fuse and the relay. When we 1st checked it had power to the fuse and relay but not coming back out of the relay to the fuel pump. So, put in a new fuel relay. Then it started up after cranking a few times, ran for 30 sec to a min, then died and wouldn't restart. Then there was no longer any power to even the fuse or coming into the fuse. With hotwiring it to get it to run, we have the power coming straight off the battery and hooked up to put power into the fuse. So it makes since that it could either be the ECM or the oil pressure switch., How can I test to see which one?
2007-06-07 07:35:47 · update #1
Ooops. How can I test both so I know which is faulty? If not both.
2007-06-07 07:37:37 · update #2
Checked all wires and replaced the oil presure switch too. It still isn't getting power to fuel relay or fuse to fuel relay. I can still hot wire it and get it to run. Anyone know what else I can check or how to check the computer? Or where the fuse is at the computer?
2007-06-10 12:12:20 · update #3
You are on the right track. The PCM or the computer as you call it does not supply the power for anything in most all of GM vehicles. What this circuit does is the PCM supplies a ground for approx. two seconds to the fuel pump relay when the truck is first turned to the ignition on position. This is done to start the fuel pump and to prime it so that there is pressurized fuel ready to go when the motor is cranked. Once the motor starts to crank and the oil pressure comes up, the part of the oil pressure switch closes and the power to the fuel pump is enabled. What you have to do is to get at the connector at the oil pressure switch and check for power when the ignition is on. If that is good, jump the wires that go back up to the relay and see if you now have power and the truck should start. If no power at the connector from battery, there is probably a fusible link blown or something like that. You will have to chase that back. If you have power to the switch but no power at the fuse or relay when you jump it, there is a broken wire between the fuse/relay area and the pressure switch. It all is good, you need a new oil pressure switch. Get a wiring diagram so you know which circuit is which. We used to give them to anybody who wanted them where I used to work. Good luck.
2007-06-07 15:58:51 · answer #1 · answered by Deano 7 · 0⤊ 0⤋
I don't have a wiring schematic in front of me. But the fuel pump is ran two different ways. The PCM sees rpm and turns on the fuel pump relay. The oil pressure switch receives voltage with pressure and turns on fuel pump relay. I have replaced pcms for not powering the relay. Usually if you crank long enough the the vehicle will start with the oil pressure switch. I usually have a wiring schematic. But remove the fuel pump relay. Use a test light or DVOM to verify PCM is sending a ground. With engine off key on. I would touch the terminals and see what has power and grounds or open. Then crank vehicle and see if it has another ground. Then the pcm is working. The fuel pump will be grounded until it receives voltage. I usually jump the relay at the terminals (the two largest female spades)from the power source to the fuel pump. If no power to relay with key on engine off. Then check the fuses under the hood. I have only had to replace one under hood fuse box for not having power. A test light will tell you the basics quickly. Pick up a Chilton manual with wire schematics. I would be more than happy to walk you through the process.Its fairly easy with a wiring schematic.
2007-06-07 02:45:47 · answer #2 · answered by joe b 2 · 3⤊ 0⤋
You write that you can hardwire and the truck runs fine. So I that would mean that the computer is working fine. So focus on finding a lose wire or a short TO the fuse.
It is not a good idea that you hotwire the electrical connection. Fuse is there to prevent electrical fire. Also, certain cars have and fuel cutoff switch (triggered by an accident or hard bump). Sometimes they are close to the fuel tank (like in the trunk in a car).
2007-06-06 21:38:31 · answer #3 · answered by Lover not a Fighter 7 · 1⤊ 0⤋
1992 Suburban
2016-09-28 02:50:10 · answer #4 · answered by ? 4 · 0⤊ 0⤋
I recently had the same problem with the daughters 92 gmc , check on the passenger side fire wall and remove the black t shaped wire harness cover and check the wires on the wiring connector block found behind it and also check for fusable links in wire harness . I,d also recomend checking your ecm fuse in your main fuse panel inside truck dash as her pick up had burnt the fuse when we hard wired it to test the fuel pump the problem on her 92 gmc was burnt wire at firewall junction box and burnt ECM fuse
2007-06-08 05:12:45 · answer #5 · answered by lescurd 2 · 1⤊ 0⤋
I think there is a short in the wiring
Could it be the fuel pump relay switch?
2007-06-06 21:02:38 · answer #6 · answered by ♥ gina ♥ 4 · 0⤊ 0⤋
remove rlay test all four pins with test light one has constant power one has power with key on if both power sources are good, jumper the pin that is straight acrossed from key on power to ground with relay installed this will start pump. if it does test control circuit to its sources ecm and oil presure switch. testpin on oilpress switch to see if it grounds when engine cranks . if no remove sending unit crank does oil come out, if yes replace sending unit. ground test is done by putting clap of test light on pos. battery cable then light ill come on whan touched to ground.
2007-06-07 21:07:48 · answer #7 · answered by tott1 5 · 0⤊ 0⤋
have a look for a loose or broken wire,you have a short causing the relay to break.you may need to have an auto electrical check.
2007-06-06 21:07:26 · answer #8 · answered by greg e 4 · 0⤊ 0⤋
My be yu but the wires wrong
2007-06-09 18:14:45 · answer #9 · answered by Anonymous · 0⤊ 0⤋
The only thing that's wrong is that its15 years old and its big & ugly. I was 3 when that was made LOL.
2007-06-07 11:39:41 · answer #10 · answered by kingderrick89 1 · 0⤊ 1⤋