04 suburban multiple misfire/limp mode?

[Chevyman93]

Hello, I’m new to the site and hope I can get some help on this issue i have been dealing with for a few months.

So I have an 04 suburban with 223k miles. Only mods done are long tube headers and cold air intake. Due to the amount of miles I have changed o2 sensors, spark plugs, spark plug wires and coil packs. I have cleaned the throttle body and maf sensor. I have done all this with no luck. Now the issue I am having only happens on hard acceleration. The truck seems to go into limp mode or is misfiring on every cylinder. During this issue I have tried unplugging one coil pack at a time to see if it’s a specific cylinder but doing that I have no change in idle which leads me to believe every cylinder is misfiring. Now I am currently in the middle of changing the intake manifold gaskets and knock sensors hoping this will finally resolve my issue. The gaskets seem to be the upgraded replacements but wasn’t sure if they had ever been replaced since I’ve owned it since 130k miles. And other ideas what this problem could be?

 

[Chevyman93]

Here is a video to show what is happening..

 

[SnowDrifter]

What is your fuel pressure doing at the time the issue occurs? You'll need to hook up a mechanical gauge and fish it through the cowl so you can watch it whole driving. O'Reilly will rent it to you

 

[afpj]

What was the video supposed to show? I see passing an RV or something, then gradually slowing down. Is that the limp mode? Shouldn't there be a DIC warning saying it's in limp mode? Hope we weren't supposed to be listening for a particular noise. There's always a radio on in the background when trying to listen to some noise.

Curious what your fuel trims show, that can give a clue regarding vacuum leak, but fuel pressure issues as above seem more logical as a common denominator.

 

[SnowDrifter]

While I'm thinking about it: check your intake too. Some of the cheaper ones will buckle under high air draw scenarios

 

[Chevyman93]

What is your fuel pressure doing at the time the issue occurs? You'll need to hook up a mechanical gauge and fish it through the cowl so you can watch it whole driving. O'Reilly will rent it to you

Not sure what the fuel pressure is doing. I replaced the fuel pump last year because one of the lines on the fuel pump was busted so it wouldn’t hold fuel pressure with the vehicle off. I always had to prime it before starting it.

 

[Chevyman93]

What was the video supposed to show? I see passing an RV or something, then gradually slowing down. Is that the limp mode? Shouldn't there be a DIC warning saying it's in limp mode? Hope we weren't supposed to be listening for a particular noise. There's always a radio on in the background when trying to listen to some noise.

Curious what your fuel trims show, that can give a clue regarding vacuum leak, but fuel pressure issues as above seem more logical as a common denominator.

Yeah sorry that was my child watching videos in the background. It was accelerating just fine then once it shifted gears it made a popping sound and it seemed the throttle wouldn’t respond after that causing the truck to slow down. At that point I can only drive about 5-10 mph because the truck constantly stutters. If I turn the vehicle off for about 5 minutes and start it back up it would seem fine to a give it gas and stutter again. The problem corrects itself if I leave it off for a while. It runs fine if I baby it but once I get on it that’s the only time the problem occurs.

 

[Chevyman93]

I can’t remember if it was stft or ltft but it reads 25 almost all the time.

 

[Chevyman93]

While I'm thinking about it: check your intake too. Some of the cheaper ones will buckle under high air draw scenarios

Are you talking about the intake manifold or the air intake?

 

[SnowDrifter]

Not sure what the fuel pressure is doing. I replaced the fuel pump last year because one of the lines on the fuel pump was busted so it wouldn’t hold fuel pressure with the vehicle off. I always had to prime it before starting it.

But is it fine now? Get checking

Are you talking about the intake manifold or the air intake?

The intake assembly that exists prior to your throttle body