2008 Tahoe Fuel Delivery Issue?

[NarcolepticNugget]

First post on here.. hoping someone may have some knowledge as to what may be going on.

I have a 2008 Tahoe LTZ, bought it with 86k miles on it February of last year. Since then, I have had intermittent issues where under hard acceleration or WOT it spits and sputters, goes nowhere in a hurry and, if you keep the pedal down it'll eventually shift and take off somewhat like it should. Odd part is, it'll do all that then shortly thereafter it'll take off like a bat out of hell like it should under WOT.

Here's a list of things that have been done since this issues occurred:

1. Rebuilt the engine (TSP Stage 3 cam, DOD Delete kit, LS6 beehive valve springs, gaskets, etc.)
2. PaceSetter long tube headers, 3" ORY.
3. CAI
4. 3" exhaust
5. Dyno Tune
6. New 4L60E trans from GM.
7. Spark plugs & Wires
8. Throttle body position sensor.


Rebuilt the engine thinking that was the issue, once my mechanic got in there and tore everything down, had some collapsed lifters and the stock cam was scorned pretty bad. Figured I'd throw some fun parts in while we were in there.


Issue continued shortly after that, thought it might be the trans - got in there and saw excessive wear on the clutch plates / gears. Replaced it.


Issue is still persisting today, my mechanic was able to see the issue first hand after replacing the trans and taking it for a test drive. Saw it command 100% fuel but not get it.


After checking the pump & MAF he thinks it's a computer / electrical issue.

Has anyone else experienced similar problems? Any ideas as to what would cause this issue?

Apologies for the long story, thank you!

 

[techbiker]

First post on here.. hoping someone may have some knowledge as to what may be going on.

I have a 2008 Tahoe LTZ, bought it with 86k miles on it February of last year. Since then, I have had intermittent issues where under hard acceleration or WOT it spits and sputters, goes nowhere in a hurry and, if you keep the pedal down it'll eventually shift and take off somewhat like it should. Odd part is, it'll do all that then shortly thereafter it'll take off like a bat out of hell like it should under WOT.

Here's a list of things that have been done since this issues occurred:

1. Rebuilt the engine (TSP Stage 3 cam, DOD Delete kit, LS6 beehive valve springs, gaskets, etc.)
2. PaceSetter long tube headers, 3" ORY.
3. CAI
4. 3" exhaust
5. Dyno Tune
6. New 4L60E trans from GM.
7. Spark plugs & Wires
8. Throttle body position sensor.


Rebuilt the engine thinking that was the issue, once my mechanic got in there and tore everything down, had some collapsed lifters and the stock cam was scorned pretty bad. Figured I'd throw some fun parts in while we were in there.


Issue continued shortly after that, thought it might be the trans - got in there and saw excessive wear on the clutch plates / gears. Replaced it.


Issue is still persisting today, my mechanic was able to see the issue first hand after replacing the trans and taking it for a test drive. Saw it command 100% fuel but not get it.


After checking the pump & MAF he thinks it's a computer / electrical issue.

Has anyone else experienced similar problems? Any ideas as to what would cause this issue?

Apologies for the long story, thank you!

I hope you didn't spend too much money on the transmission! Sounds like an electrical or fuel problem. Have you checked your fuel pressure? Who tuned your ECU?

Have you looked at your fuel pump?

 

[NarcolepticNugget]

I hope you didn't spend too much money on the transmission! Sounds like an electrical or fuel problem. Have you checked your fuel pressure? Who tuned your ECU?

Have you looked at your fuel pump?

$0 out of pocket expense on the trans thanks to a 3rd party warranty. Fuel pressure & pump checks out, was one of the first couple things checked by my mechanic.

Strictly Performance Motorsports in Kalamazoo MI did the tune.

 

[swathdiver]

Welcome aboard Ben! My first thought reading this is grounds, check and double check all the ground wires and the battery cables. Do you have access to a scan tool to check your sensors such as the MAF?

 

[NarcolepticNugget]

Welcome aboard Ben! My first thought reading this is grounds, check and double check all the ground wires and the battery cables. Do you have access to a scan tool to check your sensors such as the MAF?

MAF has been cleaned and checked as well, I do not personally have a scan tool but my local shop has had the Tahoe hooked up the last couple days scanning over everything. I've replaced a couple ground straps and the battery cables as well. Put a new battery in today actually.

 

[swathdiver]

If you're going to keep this truck and I reckon you will because of everything you've done to it and want to enjoy it, why not buy a Tech2 so you can check things out on your own? Sometimes those guys just aren't thorough enough but you will be. There's something leftover from all that work that was done that should have been fixed and was not fixed. Don't these trucks have two TPS sensors?

 

[NarcolepticNugget]

If you're going to keep this truck and I reckon you will because of everything you've done to it and want to enjoy it, why not buy a Tech2 so you can check things out on your own? Sometimes those guys just aren't thorough enough but you will be. There's something leftover from all that work that was done that should have been fixed and was not fixed. Don't these trucks have two TPS sensors?

The thought has crossed my mind to get one - I just haven't pulled the trigger. With the issue being so intermittent it makes me think it's an electrical issue. Been to three different mechanics and none can pin point the issue.

As far as the TSP sensor goes - I'm not sure if they have 1 or 2.

 

[swathdiver]

I looked at mine today and it has two TPS sensors.

 

[iamdub]

Are any codes set when it acts up? Flashing SES light? If you or a competent tech could see a live data stream, you could see what sensors are telling the PCM. If one or some suddenly tell it crazy stuff when it acts up, that would really narrow it down. There's a known issue with the throttle body wiring getting intermittent open circuits and the fix is a new plug end with a pigtail of new wiring that you splice on. I'd be suspicious that the TAC module is commanding throttle but the throttle motor just isn't responding. You'd floor it and everything else responds appropriately- trans downshifts, injector pulse width lengthens, etc. but the throttle blade never actually opens as you and the PCM expects. This would cause a sudden rich condition. Code(s) may not be set because it's at WOT and a lot of input may be ignored during this, especially with a custom tune. On a live data stream, you'd see the TAC command WOT and the injector duty cycle jump, but you'd see the TPS reporting no or little change in the throttle percentage. You'd also see the front O2s report rich.

 

[NarcolepticNugget]

Are any codes set when it acts up? Flashing SES light? If you or a competent tech could see a live data stream, you could see what sensors are telling the PCM. If one or some suddenly tell it crazy stuff when it acts up, that would really narrow it down. There's a known issue with the throttle body wiring getting intermittent open circuits and the fix is a new plug end with a pigtail of new wiring that you splice on. I'd be suspicious that the TAC module is commanding throttle but the throttle motor just isn't responding. You'd floor it and everything else responds appropriately- trans downshifts, injector pulse width lengthens, etc. but the throttle blade never actually opens as you and the PCM expects. This would cause a sudden rich condition. Code(s) may not be set because it's at WOT and a lot of input may be ignored during this, especially with a custom tune. On a live data stream, you'd see the TAC command WOT and the injector duty cycle jump, but you'd see the TPS reporting no or little change in the throttle percentage. You'd also see the front O2s report rich.

No set codes when it does this but - the CEL does come on and flash until you let off the pedal. The mechanic did say he watched it command fuel but not get it and it went lean. He stated he had it hooked up to a laptop. Like you stated, everything else seems to respond like it should it just doesn't seem to get any fuel.