2002 fuel trims loss of power after 2 hours

[mhaywoodcz]

Hey Guys,

Need a lil troubleshooting help. I have a stock 2002 Yukon Denali with 170k miles that starts acting stupid only during long road trips. We use this primarily for pulling the boat or camper to the beach our mountains.

Usually after a good 2 hours of driving, I get issues with power loss when giving more than 1/4 throttle. Below is a video of fuel trims and the cluster while giving more than 1/4 throttle, letting off and throttling again.
I see the fuel trims are +25% or more.
Seems after it fully cools down, overnight or so its ok for another few hours.
Mechanically everything is good, new transmission last week, good fluids, new coil packs, spark plugs, MAF, MAP, brakes +line etc. Learned all the proper maintenance and how to's from here.
Any thoughts?


https://youtube.com/shorts/RxArYLDK9x0

 

[mattbta]

Looks like a vacuum leak with high positive short and long terms. Would suspect intake manifold gasket, but those usually seal up after it gets hot. Check all vac lines.

 

[mhaywoodcz]

Interesting, just weird that there are no DTCs showing up. I'll dig in and see how the vac lines and check the intake manifold, it does look a little oily on the passenger side.
Thanks

 

[mhaywoodcz]

So I sent the logs and pics to Black Bear, they believe it could be a failing fuel pump. Seems to only act up when it's hot/ few hours driving. So this weekend its fuel pump and vac line check time.
Ill keep everyone posted on it

 

[strutaeng]

Yeah, after looking at that video I was going to suggest fuel delivery issues. Fuel delivery would typically affect BOTH banks pretty much equally, which is what you have.

Get yourself a fuel pressure gauge, the one with the long hose and tape it to your windshield and go for a drive. I bet the fuel trims would coincide with low fuel pressures under load. Check wiring integrity if that's the case as a sanity check.

You can try to look at waveform of the fuel pump motor commutators with a scope, but that's beyond the knowledge and access to tools of most DIYers, including myself.

 

[nonickatall]

I think a 2002 has a fuel filter, so when your filter was last time changed? Even the fuel pressure regulator can have such problems. So the idea of strutaeng is good, to check the fuel pressure.

It can be the fuel pump, but i would swap filter and fuel pressure regulator first. Cost only a few dollar and should be replaced with a new fuel pump anyway..

 

[Fless]

I'd do the diagnostic work first, especially the fuel pressure monitoring. Confirm that's the problem before changing parts; otherwise one never knows which part(s) fixed it.

Fuel filter, if present, could be suspect, as could the FPR.

 

[Larryjb]

Leaking intake manifold gaskets are so common on these years I wouldn't rule that out just yet. It's also an easy and cheap fix.

 

[Alex_M]

I concur that this sounds like a fuelling issue. Just had nearly the exact same symptoms on a Silverado which ended up being a weak fuel pump.

 

[mhaywoodcz]

Thanks for the suggestions guys, I replace the pump yesterday. Found that who ever did the wiring last time only twisted the wires together and heat shrinker them, no solder or crimps or anything. Anyways I redid the connections with crimps and heat shrink and put it all back together. The new pump sounds healthier, weather it was the wiring or pump itself, both have been remedied.
Fuel filter was changed about 8k ago, and I tested the pressure with a gauge on the old pump. Not a drive but a key on engine off, it was 58psi.
So, Im going to do an E-fan conversion over the next few days and then do some driving.
We will see what happens.

As a precaution, I have the intake gasket, knock sensors and harness ready if needed.
Keep y'all posted