Three random shut offs while slowing to a red light.

[Doubeleive]

No everything stays on just like its running. Radio good and a/c fans still run. And given the battery light not coming on, it doesn't even think the alternator stopped. Its crazy. And just my luck, I put all this money in and now some gremlin problem.

Like on a normal stall, you would expect dash lights, yeah? Like battery at minimum. Also every time, has been slowing down for a stop, or as of today, a turn.

Well I would start with those cables for beginners

 

[petethepug]

Do the remedial stuff known to really get these trucks down. Just chalk it up to missed maintenance.

* Replace carbon canister.
* Replace battery +\- cables.

You’ll have a clean slate after that for diagnostics and know right away if you had a bad ground or wire and\or a leaky carbon canister.

There’s also a slight possibility that the previous owner replaced the fuel pump with a cheap overseas specials and it’s doing what those POS time bomb like things to … act weird and send you on a wild goose chase but not fail 100%.

 

[CaptainAmerica1]

Check your ltft sounds like the beginnings of a vacuum leak…

 

[olliec420]

Battery cables and main fuse done.

 

[olliec420]

Do the remedial stuff known to really get these trucks down. Just chalk it up to missed maintenance.

* Replace carbon canister.
* Replace battery +\- cables.

You’ll have a clean slate after that for diagnostics and know right away if you had a bad ground or wire and\or a leaky carbon canister.

There’s also a slight possibility that the previous owner replaced the fuel pump with a cheap overseas specials and it’s doing what those POS time bomb like things to … act weird and send you on a wild goose chase but not fail 100%.

The carbon canister for the evap? Could that be related somehow? I did that one already though.

 

[olliec420]

Check your ltft sounds like the beginnings of a vacuum leak…

LTFT? Lon term fuel trim? What number should I be seeing?

 

[petethepug]

Yup, that one at the rear, under the truck by the fuel tank. It loves to get cranky and let loose all the carbon pellets into the fuel system. With that out of the way, knowing it wasn’t leaking pellets, you can diagnose off a better baseline now.

The carbon canister for the evap? Could that be related somehow? I did that one already though.

 

[olliec420]

Yup, that one at the rear, under the truck by the fuel tank. It loves to get cranky and let loose all the carbon pellets into the fuel system. With that out of the way, knowing it wasn’t leaking pellets, you can diagnose off a better baseline now.

Gotcha, yeah I did that in the spring. It let loose and the lines clogged but I got it though.

 

[petethepug]

Ugh, if it was letting pellets loose keep in the back of your mind that the pellets may have migrated into the tank and made their way into the fuel pump causing random obstructions to fuel delivery.

The only to cure it, as well as diagnose it is to drop the tank, pull the f/p, swab the tanks interior and blow out the line in the system. Of course if your in there it only makes sense to replace the OEM f/p (with another OEM) as they’re good for about 10yr/100k mi.

 

[olliec420]

Ugh, if it was letting pellets loose keep in the back of your mind that the pellets may have migrated into the tank and made their way into the fuel pump causing random obstructions to fuel delivery.

The only to cure it, as well as diagnose it is to drop the tank, pull the f/p, swab the tanks interior and blow out the line in the system. Of course if your in there it only makes sense to replace the OEM f/p (with another OEM) as they’re good for about 10yr/100k mi.

Hmm i thought about that. But the fuel pump picks up from the middle all the way around, no? I can't image a few pellets would stop the flow

 

[petethepug]

Correct, pellets won’t stop the flow, but they will obstruct the line and gather at the point of highest velocity. When velocity slows, volume decreases at a huge factor from the obstruction.

If, and I say if, you have rouge pellets in the system, your engine will starve of fuel at idle. Once the suction of the fuel pump stops calling all the pellets together, the obstruction falls apart. Viola, all is back to normal without any DTC being triggered.

 

[olliec420]

Correct, pellets won’t stop the flow, but they will obstruct the line and gather at the point of highest velocity. When velocity slows, volume decreases at a huge factor from the obstruction.

If, and I say if, you have rouge pellets in the system, your engine will starve of fuel at idle. Once the suction of the fuel pump stops calling all the pellets together, the obstruction falls apart. Viola, all is back to normal without any DTC being triggered.

WHich line are you thinking? from tank to rail?

 

[petethepug]

That & the swirl pot that the f/p lives in, as well as the mesh filter or what’s left of it on the base, if GM installed that version in your truck.

 

[olliec420]

Check your ltft sounds like the beginnings of a vacuum leak…

Does this tell us anything?

 

[Fless]

Generally speaking, short term fuel trims would be used for vacuum leak diagnostics. Document the STFTs at idle, then at 1500 or 2000 rpm and compare.

Higher positive STFTs at idle (say, >+10% or so) can indicate unmetered air getting in past the MAF and the O2 sensors trying to manage that, dumping fuel into the engine.

If the STFTs get significantly lower at higher rpms, a vacuum leak is likely. This is because the higher rpm needs more air, and the vacuum leak can add only a small bit of air -- enough, though, to impact the trims at idle. At higher rpms most of the needed air comes through the proper passages and is metered more correctly.

The LTFTs are learned at various rpms and load conditions. Your true total fuel trim (on one bank) is the sum of the STFT and the LTFT at a given rpm (after the rpms have settled). If STFT is -3% and LTFT is +4%, the net FT is +1. Total single bank fuel trim of 5% or under is ideal; be concerned when it's over 10%.

 

[olliec420]

Generally speaking, short term fuel trims would be used for vacuum leak diagnostics. Document the STFTs at idle, then at 1500 or 2000 rpm and compare.

Higher positive STFTs at idle (say, >+10% or so) can indicate unmetered air getting in past the MAF and the O2 sensors trying to manage that, dumping fuel into the engine.

If the STFTs get significantly lower at higher rpms, a vacuum leak is likely. This is because the higher rpm needs more air, and the vacuum leak can add only a small bit of air -- enough, though, to impact the trims at idle. At higher rpms most of the needed air comes through the proper passages and is metered more correctly.

The LTFTs are learned at various rpms and load conditions. Your true total fuel trim (on one bank) is the sum of the STFT and the LTFT at a given rpm (after raising the rpms). If STFT is -3% and LTFT is +4%, the net FT is +1. Total single bank fuel trim of 5% or under is ideal; be concerned when it's over 10%.

STFT at idle (when I've measured) are no where near 10, like 1% or less. BUT is it POSSIBLE that the EVAP valve or something like that is staying open or partially open intermittently as I'm having intermittent problems?

I dont think a permanent leak such as a crack in a plastic hose or something would show intermittent symptoms that Im seeing.

 

[olliec420]

Just an update, changed the positive and negative cables 2-3 weeks ago and it has not happened again... yet.

Fingers crossed!

 

[olliec420]

No more shut downs. Volts higher all around. Looks like that might have did it!