Inconsistently odd fuel delivery issues (I THINK?)

[Marky Dissod]

Over the past year, my '02 Tahoe Z71 has SOMETIMES suffered the following IRREGULARLY INTERMITTENT symptoms:

*When I step on the throttle, I get nowhere near the expected acceleration, like maybe late 80s 4.3L V6 acceleration at best?
If I initially get the expected acceleration, it peters out and cannot exceed 3600RpM, even if I floor it.
*There is a very small but nonzero chance that the fuel pump will 'take a break' with no prior symptoms or indications.
If it 'takes a break', the break will last at least 30min (during which I & others can't smell any fuel despite desperate overcranking)
*There is a slightly larger chance that the fuel pump will warn of an impending lunch break,
by stumbling and under-performing slightly, and getting worse and worse, like it's tiring out and 'needs' a 'break'.

The longest 'break' has been over 2hr. Once 'break time' is over, it acts normally for at least 20min.
However, there have been entire months (come to think of it, WINTER!) during which I suffered no symptoms.

Obviously, the 1st guess is the fuel pump, which for all I know may be GM OE from the '02 assembly line?
I'm asking for any other guesses, BESIDES the fuel pump itself.
What could make the fuel pump take an unapproved/unauthorised break, when I want it to keep on working?

Thank you all in advance for your consideration.

 

[99Sierra2500]

Clean maf and tb

 

[Marky Dissod]

Clean maf and tb

Should be ok to replace MAF & throttle body with cleaner spares, then.
Thanks, will do today or tomorrow (lucky enough to be able to borrow a '12 Caprice PPV 6.0L by Holden).

Please keep the suggestions coming, and thank you @99Sierra2500!

 

[ORVietVet]

"Obviously, the 1st guess is the fuel pump, which for all I know may be GM OE from the '02 assembly line?
I'm asking for any other guesses, BESIDES the fuel pump itself.
What could make the fuel pump take an unapproved/unauthorised break, when I want it to keep on working?"

Get a fuel pressure gauge and snake out under back of hood and attach to w/s and read the pressures while driving. Have you changed the fuel filter? If do a pump, do the filter.

 

[99Sierra2500]

Should be ok to replace MAF & throttle body with cleaner spares, then.
Thanks, will do today or tomorrow (lucky enough to be able to borrow a '12 Caprice PPV 6.0L by Holden).

Please keep the suggestions coming, and thank you @99Sierra2500!

Maybe, though the cleaner kit is pretty cheap too:

https://www.walmart.com/ip/CRC-Mass-Air-Flow-Throttle-Body-Single-Use-Cleaner-Twin-Pack-Kit/36755294

 

[ORVietVet]

Maybe, though the cleaner kit is pretty cheap too:

Robot or human?

Nver seen a dirty MAF or failing MAF kill an engine. Not saying it can't though. T/B either.

 

[99Sierra2500]

Nver seen a dirty MAF or failing MAF kill an engine. Not saying it can't though. T/B either.

He says it's running bad (w/o talking about the fuel pump) by servicing the maf and tb it's a function check, and spot other problems. Otherwise w/o guessing fuel pump, which is likely, I'd say pedal, it is dbc pretty sure. Live data as well. Except the no start when hot makes the fuel pump the likely problem.

 

[ORVietVet]

Carry a rubber mallet with you and next time it dies and will not restart, tap the bottom of the tank and see if starts right after that. May well be pump if does start that way. BUT, a pressure reading removes all doubt. You may find debris in the tank as well.

 

[Tonimus]

Going back to my first truck, it was my fuel sock that caused similar issues. Granted it wasn't a GMT800, but that's also a non-zero chance to be plugged up.

 

[ORVietVet]

He says it's running bad (w/o talking about the fuel pump) by servicing the maf and tb it's a function check, and spot other problems. Otherwise w/o guessing fuel pump, which is likely, I'd say pedal, it is dbc pretty sure. Live data as well. Except the no start when hot makes the fuel pump the likely problem.

Without a doubt, MAF and T/B cleaning may help but the info sounds like a pump.

 

[Marky Dissod]

Get a fuel pressure gauge and snake out under back of hood and attach to w/s and read the pressures while driving. Have you changed the fuel filter? If do a pump, do the filter.

I change the fuel filter annually, so that's unlikely but possible.
What else ...

Never seen a dirty MAF or failing MAF kill an engine. Not saying it can't though. T/B either.

Which makes me wonder about the electrical 'command gates' that would 'tell the fuel pump to shut down'.
In other words, is my fuel pump receiving a lie that causes it to think I'm no longer driving on the highway @ 70MpH, and that it's time to shut down,
so that I can unintentionally cause a traffic snarl and get thousands of stinkeyes?

Otherwise w/o guessing fuel pump, which is likely, I'd say pedal, it is dbc pretty sure.

'02 L59 is physical cable throttle telling the pcm (not electrical wire throttle that the pcm can disagree with).

Except 'no start when hot' makes the fuel pump the likely problem.

I know, I agree, others reading this thread deserve to be reminded of what ought to be obvious ...

Carry a rubber mallet with you and next time it dies and will not restart, tap the bottom of the tank and see if starts right after that.
May well be pump if does start that way. BUT, a pressure reading removes all doubt.

Recently loaned the no-spark shot filled mallet that I'd been carrying for years to a good friend who has thanked me, but not mentioned it since ...

You may find debris in the tank as well.

Does that mean, 'maybe not just a pump, but a new tank'?
or,
'new pump, and clean the ever-lovin schidt out of the tank before remounting it'?

Going back to my first truck, it was my fuel sock that caused similar issues. Granted it wasn't a GMT800, but that's also a non-zero chance to be plugged up.

Doesn't this effectively mean, 'new fuel pump' anyway?

Without a doubt, MAF and T/B cleaning may help, but the info sounds like a pump.

So stipulated.

 

[Tonimus]

Doesn't this effectively mean, 'new fuel pump' anyway?

No, but it does mean dropping the tank and getting at it. Fuel Pump Strainer is the technical name.

 

[99Sierra2500]

'02 L59 is physical cable throttle telling the pcm (not electrical wire throttle that the pcm can disagree with).

I like the cable better. Drive by wire pedal is a service item, every 80k, can cause a bunch of problems when it goes bad. One thing you can check if you have the air intake tube off is if the cable is making the throttle body butterfly move through it's entire range, probably is, but doesn't hurt to check.

 

[CPB]

I would measure fuel pressure if you're leaning towards it being a fueling issue.

 

[Marky Dissod]

I like the cable better. Drive by wire pedal is a service item, every 80k, can cause a bunch of problems when it goes bad.
One thing you can check if you have the air intake tube off is if the cable is making the throttle body butterfly move through it's entire range,
probably is, but doesn't hurt to check.

Throttle body moves fluidly through its total range.

Anyone else have any odd ideas?
Like, what could trick the fuel pump into thinking the key is no longer in the 'RUN' position, or something odd like that?

Odds are I'll buy a fuel pump and a new mallet this coming weekend, but I want to rule out other stuff.

 

[Tonimus]

If you want to make sure it's not the relay, you can check the control side. Rig up a little test light to the "Prime" spot in the underhood fuse box. Right next to the fuel pump relay, there's a single receptacle. This is hot when the fuel pump is energized. It allows priming the truck without turning the key if you apply power to it.

 

[99Sierra2500]

I have had cars stall when the AC is on due to a bad Idle Air Control valve, such as having a load, it's hot, and at idle; not driving and dying though.

 

[Marky Dissod]

I have had cars stall when the AC is on due to a bad Idle Air Control valve, such as having a load, it's hot, and at idle; not driving and dying though.

Not sure if this is a separate problem, but ... first cold start of any day, soon as it goes into COLD closed loop, and until it reaches full operating temp,
if the AC is on, my engine will threaten to / might shut off, no stumble or stutter.
If it doesn't shut off, it'll 'idle' as low as 200RpM for up to 4 sec before the idle fixes back @ 625RpM (tuned), like the idle was trying to 'limbo'.
No amount of tuning has had any permanent effect on this warmup symptom.
Rarely this symptom shows up during off-/on-ramps; luckily I'm very talented at left-foot braking so I can artificially raise the idle with my right foot.

I've tried 3 new Idle Air Control valves and two identical throttle bodies, no effect.
Should I start a new thread about this, or could this be related?

 

[Marky Dissod]

Just read this thread.
Gonna put a Crank Position Sensor in my parts derringer.

Anything else CHEAP, & QUICK & EASY to remove & replace, that I can put in my parts derringer?
(Parts cannon is for expensive stuff that is NOT QUICK & EASY to R&R).

 

[99Sierra2500]

Just read this thread.
Gonna put a Crank Position Sensor in my parts derringer.

Anything else CHEAP, & QUICK & EASY to remove & replace, that I can put in my parts derringer?
(Parts cannon is for expensive stuff that is NOT QUICK & EASY to R&R).

I'm leery of changing parts, as you said you have tried multiple parts like IAC's, and TB's. It very well could be a CPS, or the Fuel Pump; besides what ORVietVet suggests checking the fuel pressure, try a vacuum gauge on the intake, the intake could have bad gaskets, or be cracked. Before changing anything.