Weird Starting Issue After Truck Sits More Than A Few Hours

[TylerHagerdorn]

I looked under the vehicle and they had to run new metal fuel lines from the pump to the filter and the filter to the engine and the line running from the pump to the filter appears to have a very significant bend that looks like it could be kinked. The fpr isn't leaking. I primed the system five times this morning before starting and it almost started but then didn't. Had to hold my foot to the floor. It started but was a little rough until I gave it some gas and it cleared up and then is perfectly fine all day long. Fires up like no issues. Just when it sits for more than 6 or 8 hours does it have this issue. Could it be as simple as a line that's almost kinked? Again it's the line coming from the tank to the filter.

 

[Fless]

Could be lots of things. Injector(s) leaking down, bad fuel pump, bad FPR, etc. Still waiting for those cold fuel pressure readings to see what's there, and if it's leaking down quickly or not much.

 

[TylerHagerdorn]

Could be lots of things. Injector(s) leaking down, bad fuel pump, bad FPR, etc. Still waiting for those cold fuel pressure readings to see what's there, and if it's leaking down quickly or not much.

I can tell you the fuel pump is not bad. I can also tell you that the fpr is not bad either. I don't own a fuel pressure tester and I'm not buying a bunch of stuff that I don't really need. I don't have anyone I know that has a tester either. Pretty sure fuel pressure is not the problem. It does not seem like it's starving for fuel. But again why would I get a composition sensor circuit low code and a purge valve circuit code for a leaking injector? That doesn't make any sense to me. I'm trying to figure out why I have those codes, because that's going to 99 percent be the cause of the issue.

 

[89Suburban]

Can you rent a FPT from somewhere?

 

[Fless]

Yes, many auto parts places will rent them for free. You put down a deposit on a credit card and it's refunded when you take it back within the alloted time, usually days.

Also, the fuel composition sensor issue has everything to do with how the ECM/PCM meters the fuel. Why not do the diag procedure on the FCS circuit and see where that takes you?

 

[Fless]

I can tell you the fuel pump is not bad. I can also tell you that the fpr is not bad either. I don't own a fuel pressure tester and I'm not buying a bunch of stuff that I don't really need. I don't have anyone I know that has a tester either. Pretty sure fuel pressure is not the problem. It does not seem like it's starving for fuel. But again why would I get a composition sensor circuit low code and a purge valve circuit code for a leaking injector? That doesn't make any sense to me. I'm trying to figure out why I have those codes, because that's going to 99 percent be the cause of the issue.

You won't necessarily get a code for an injector that's leaking down, but if you have one it could be dumping fuel into the oil. Eventually that will thin the oil and ruin the bearings. Does the oil smell like gas?

Other than what I've mentioned, without further useful information, I got nuttin'. Maybe someone else has an idea.

 

[TylerHagerdorn]

Yeah I know parts stores do the "free" loaner tools lol Ive worked at either O'Reilly or Zone or Advance the last 11 years. I just discovered that my truck is supposed to have a 145 amp alternator via the RPO code and all the options it has, and someone at some point installed a 105 amp, probably because it was cheaper and I know how customers are. And I know from plenty of experience of working on vehicles and selling parts that a lower amp alternator will absolutely cause electrical issues, especially on GM vehicles. And both codes I have are for circuit low. There is no telling how long the alternator has been on there. But I'm sure that could be the cause of a lot or all of my electrical issues going on

 

[TylerHagerdorn]

You won't necessarily get a code for an injector that's leaking down, but if you have one it could be dumping fuel into the oil. Eventually that will thin the oil and ruin the bearings. Does the oil smell like gas?

Other than what I've mentioned, without further useful information, I got nuttin'. Maybe someone else has an idea.

No fortunately the oil does not smell like gas.

 

[rockola1971]

Yeah I know parts stores do the "free" loaner tools lol Ive worked at either O'Reilly or Zone or Advance the last 11 years. I just discovered that my truck is supposed to have a 145 amp alternator via the RPO code and all the options it has, and someone at some point installed a 105 amp, probably because it was cheaper and I know how customers are. And I know from plenty of experience of working on vehicles and selling parts that a lower amp alternator will absolutely cause electrical issues, especially on GM vehicles. And both codes I have are for circuit low. There is no telling how long the alternator has been on there. But I'm sure that could be the cause of a lot or all of my electrical issues going on

If you were running the heat on full blast along with seat heaters on while cranking the stereo then maybe yes but if all those are off then a 105a alternator is not going to be the cause of your problems. Circuit low could be wiring or component shorted pulling down the feed to the composition sensor or even a corroded connector in the composition wiring from the sensor or all the way back to its feed. These conditions both would cause low voltage to the composition sensor and the sensors output voltage being lower than what the PCM expects. Time to get the voltmeter out and factory troubleshooting chart with known voltages.

And as many have said....the grounds corroded. A very common problem on C and K chassis.

 

[TylerHagerdorn]

If you were running the heat on full blast along with seat heaters on while cranking the stereo then maybe yes but if all those are off then a 105a alternator is not going to be the cause of your problems. Circuit low could be wiring or component shorted pulling down the feed to the composition sensor or even a corroded connector in the composition wiring from the sensor or all the way back to its feed. These conditions both would cause low voltage to the composition sensor and the sensors output voltage being lower than what the PCM expects. Time to get the voltmeter out and factory troubleshooting chart with known voltages.

And as many have said....the grounds corroded. A very common problem on C and K chassis.

There's no corroded grounds I've already replaced them all. Running a lower amp alternator is NOT good for a vehicle that's supposed to have a higher amp. Especially on a GM. It can cause severe electrical issues. My heat is always on full blast and seat heaters are running and I always have the radio cranking because I like my music and the RSE is running because my son likes watching movies and of course it gets really bad at night when all the lights are on and they pulsate as well and my volt gauge drops significantly