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Car Forum / Chevrolet / Chevrolet Trucks / August 200689 GMC 5 second run
Went out today fired up the truck it ran for 5 seconds and shuts off... It shuts the fuel off, thought oil pressure at first not letting fuel pump run, but it has almost 60 psi at start up. Ran codes and got a 45 (rich O2 sensor)... it only runs on the 5 second timer... Anyone with the quick fix on this ??? I looked back through the posts I'm sure it's there somewhere but didn't see it yet... > Went out today fired up the truck it ran for 5 seconds and shuts off... It > shuts the fuel off, thought oil pressure at first not letting fuel pump [quoted text clipped - 3 lines] > I looked back through the posts I'm sure it's there somewhere but didn't > see it yet... I guess I'll try the oil pressure switch... I know it has two circuits in it one for gauge and one for engine running.... I'll see what that does... > > Went out today fired up the truck it ran for 5 seconds and shuts off... It > > shuts the fuel off, thought oil pressure at first not letting fuel pump [quoted text clipped - 6 lines] > I guess I'll try the oil pressure switch... I know it has two circuits in it > one for gauge and one for engine running.... I'll see what that does... Don't think it will help and don't have enough info to try to help. Did you check for any stored codes? Al >> > Went out today fired up the truck it ran for 5 seconds and shuts off... > It [quoted text clipped - 16 lines] > > Al Like I said in the initial post the only code is a 45 It's a 5.7 1989 GMC TBI ? it starts runs for about 3-5 seconds then shuts off... when it shuts off the fuel stops instantly. We used a squirt bottle and sprayed fuel in and it keeps running. Going for the op switch now try that and see if it fixes it... I can't remember for certain; but I think the oil pressure sender for the gauge is separate from the oil pressure switch for the fuel pump. I had one fail on my '88. There's also a fuel pump relay and a fuse... but I can't remember whether they are used during start-up or while driving. It seems to me that the oil pressure switch acts through the fuse and relay. The fuse is in a black "holder" mounted to the firewall... it pulls out from the bottom if I remember correctly. You can also activate the fuel pump "manually" by using a jumper wire in the ALDL plug under the dash... I drove mine that way for a week or two while my rebuilt ECU was on back-order. That way you can get the thing running so you have oil pressure to check the switch if you want to. I would check both the fuse and the relay. Sorry... it's been years since I had that truck. David > Like I said in the initial post the only code is a 45 > > It's a 5.7 1989 GMC TBI ? it starts runs for about 3-5 seconds then > shuts off... when it shuts off the fuel stops instantly. We used a squirt > bottle and sprayed fuel in and it keeps running. Going for the op switch > now try that and see if it fixes it... > I can't remember for certain; but I think the oil pressure sender for > the gauge is separate from the oil pressure switch for the fuel pump. I [quoted text clipped - 18 lines] >> bottle and sprayed fuel in and it keeps running. Going for the op switch >> now try that and see if it fixes it... OP switch not the answer, O2 sensor not the answer. Still starts and runs for the 3-5 seconds or so and then shuts off... Luckily we had a donor truck same year same engine that we scrapped a few months ago, but saved the harness, TBI, O2 all sensors and computer... (to put into an older car) so... we might throw the computer on it next what the hell... I'll look at my wiring schematic and see if I can see which ones to jump and see if that lets it run for any length of time. It is weird because we use the truck regularly... we parked it one night next morning came out and now this ... never had a problem before it has been the most dependable truck. It only has 215,000 miles on original engine, never had anything apart on the engine. Holds 40 psi. oil pressure in gear at idle, almost 60 psi. diving down the road even checked it with a manual gauge and it's right. The reason it starts is because the computer turns on the fuel pump itself, to build up pressure so it starts easily... so it's probably not the computer. From what you describe, I would bet on the fuel pump fuse mounted on the firewall in the engine compartment. David >>> Like I said in the initial post the only code is a 45 >>> [quoted text clipped - 16 lines] > in gear at idle, almost 60 psi. diving down the road even checked it with > a manual gauge and it's right. > The reason it starts is because the computer turns on the fuel pump > itself, to build up pressure so it starts easily... so it's probably not > the computer. > From what you describe, I would bet on the fuel pump fuse mounted on > the firewall in the engine compartment. > David Double checked the fuse it is good, put a meter on and monitored it. That is the fuse that runs the pump by the computer. It has 12.6 v until pressure builds then it turns off. Start engine and it has voltage even after the engine shuts off, but it is not injecting. For what it's worth, we..... Swapped TBI's found no vacuum leaks or any other stuff. Started same thing, swapped computers no change... Right now throwing on the MAP and the whole cluster there... Didn't fix it.... This eliminates almost everything , but possibly the distributor isn't giving the ref. pulse, but the hold down bolt is froze tight into the aluminum manifold or that would have been changed already too..... Going out now to try to loosen up the bolt and get it moving... Ready to throw on a carb.... I hate carbs and hate fuel injection worse when it doesn't work... >> The reason it starts is because the computer turns on the fuel pump >> itself, to build up pressure so it starts easily... so it's probably not [quoted text clipped - 18 lines] > Ready to throw on a carb.... I hate carbs and hate fuel injection worse > when it doesn't work... P).S. not the distributor..... I might try retorqueing the lug nuts.... lol What about the relay for the fuel pump? Maybe the relay isn't switching... so the power isn't getting to the pump when the computer releases it? Wish I could remember more about how that all worked. David >>> The reason it starts is because the computer turns on the fuel pump >>> itself, to build up pressure so it starts easily... so it's probably not [quoted text clipped - 21 lines] > P).S. not the distributor..... I might try retorqueing the lug nuts.... > lol Yes replaced that too.... the list is so long now only one I can think of now is 5 gal of gas and a match... It's nice having a running truck to swap parts from, I know it's going to be something sooooo stupid that I just keep overlooking it. I listened to the pump it sounds like it runs before starting and then doesn't run again until it shuts off... We are hooking up the fuel pressure gauge right now to verify that it loses pressure completely before turning back on. I'm hoping it's not the pump, we just replaced that along with the sender unit, fuel lines etc... about a year ago... > What about the relay for the fuel pump? > Maybe the relay isn't switching... so the power isn't getting to the [quoted text clipped - 27 lines] >> P).S. not the distributor..... I might try retorqueing the lug nuts.... >> lol > Yes replaced that too.... the list is so long now only one I can think of > now is 5 gal of gas and a match... [quoted text clipped - 38 lines] >>> P).S. not the distributor..... I might try retorqueing the lug nuts.... >>> lol How about jumping a 12 volt line direct to the pump and seeing if it runs then.  SignatureSteve W. Near Cooperstown, New York Life is not like a box of chocolates it's more like a jar of jalapenos- what you do today could burn your a.s tomorrow! My oil pressure switch on my 89 K5 connected or not, has no effect on whether it runs or not. Disconnected, it registers max pressure. Have you tried replacing the oxygen sensor ? Do you have any intake manifold leaks ? TBI base...etc. ? >>> > Went out today fired up the truck it ran for 5 seconds and shuts >>> > off... [quoted text clipped - 27 lines] > bottle and sprayed fuel in and it keeps running. Going for the op switch > now try that and see if it fixes it... Ended up being the ground wire from pump at tank to frame. It was corroded on the frame. Found it when we went to pull the tank to replace the fuel pump. It had good pressure one time then low then good... It was intermittent... The fuel pressure gauge would fluctuate from 9-13 psi. run bad then pump good and stay at 13 psi and run good. Ran ground into ground that comes back to the sender unit for the tank sender also adjusted the fuel regulator up to hold 15 psi and it runs awesome... Can't believe the a.sholes at GM would rely on a frame grd. when they have a grd. wire running all the way back there already... > My oil pressure switch on my 89 K5 connected or not, has no effect on > whether it runs or not. Disconnected, it registers max pressure. [quoted text clipped - 32 lines] >> bottle and sprayed fuel in and it keeps running. Going for the op switch >> now try that and see if it fixes it... > Ended up being the ground wire from pump at tank to frame. It was corroded > on the frame. Found it when we went to pull the tank to replace the fuel [quoted text clipped - 6 lines] > Can't believe the a.sholes at GM would rely on a frame grd. when they have a > grd. wire running all the way back there already... Run another wire for the ground. Or just clean up the original ground. Don't use the sender ground. They had a good reason for not using it. Al |
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