2002 Yukon XL 2500 6.0 4x4

[Brandon Froehlich]

Just a little problem with my new truck guys. 02 yukon 6.0 350k on the clock. I know no history, codes include random misfire and knock sensor.

Truck bogs badly unset throttle, heavy or light randomly. No rhyme or reason as if it's not getting fuel.

I immediately replaced plugs and fuel filter, checked wires cleaned throttle body and maf fixed g.m.'S notorious broken manifold bolts....and still getting this problem.

I suspected clogged cats but it's random which leads me to think it's a pump on its way out.

Someone else is telling me a bad knock sensor could cause this issue but I'm not sure.

The truck literally falls on its face with anything more than very little throttle. Also gets an extreme hollow sound from the intake as if there was no filter or box. Other times runs perfect, idles great no matter what etc...

 

Like I said 350k on the clock, factory cats, truck sounds good and seems to be breathing well do not know any mechanical history whatsoever

Any help is greatly appreciated

Thanks guys!

[Formulabruce]

Clean the throttle body with throttlebody Cleaner, clean the throttle plate, has to be spotless. Clean the MAF with MAF cleraner

Put Copper never seize on those spark plug threads.

my thought , start with the easy things

[Brandon Froehlich]

Already did all of that unfortunately, when I swapped plugs I replaced wires with some delcos I had cleaned the throttle body specifically with throttle body cleaner, as well as the maf with specific maf cleaner. I hate spending money on these "particular" cleaners but I did because I know how finicky these engines can be. I have extra everything from my 04 which was the same exact truck mechanically so I'm going to switch out a bunch of the easy items.

I am curious though would in fact a bad knock sensor cause the runability issue? I can't see it having the ability to adjust the timing THAT much to make it run THAT poorly at speed. Just curious

[Raptordude]

Even if it's not your problem, with 350k and the original cats they have to be super clogged

 

 

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[Formulabruce]

The throttle unit could be sucking air, they do get worn and need replacement

[Brandon Froehlich]

Throttle unit?

[Brandon Froehlich]

Would it be beneficial to disconnect the fuel filter and blow back through the fuel line because it is almost like there is junk in the tank being sucked into the sock and preventing good fuel flow

[Brandon Froehlich]

I only say this because I have never experienced a pump slowly going out they either work or don't

[Formulabruce]

Throttle unit?

YES, the on3e you cleaned after removing the fresh air intake assembly, the throttle PLATE is right there, has a motor, they can have issues at high miles..

[Brandon Froehlich]

This isn't a dbw vehicle though it is still cable driven t/b

[davester]

My '04 Sierra 6.0L had a fuel pump that could supply enough pressure at idle for the engine to run OK, but once you hit the gas, fuel pressure would drop from around 50 to under 10 psi. The engine would still run, but very poorly.

[Brandon Froehlich]

free reving there doesnt seem to be any issues, only randomly happens while driving. and when it does it acts like when you hit the rev limiter in park but driving down the road. can only barely ease on the throttle to get it to move down the road. it literally falls directly on its face

[Brandon Froehlich]

So...pulled injectors to clean and found 3 partially stuck open and ALL completely full of GUNK cleaned and replaced bad ones and she is running pretty good, still flashing at times for a misfire but it's unnoticeable so I'm leaning towards cats but they aren't causing an issue.

[Mark-23]

Anyone selling their GMT800 2500 suvs? I'm looking for a Yukon XL or a suburban, I'm tired of my 1500.

[VikingTrad3r]

So...pulled injectors to clean and found 3 partially stuck open and ALL completely full of GUNK cleaned and replaced bad ones and she is running pretty good, still flashing at times for a misfire but it's unnoticeable so I'm leaning towards cats but they aren't causing an issue.

 

 

Hey Olds man, just wondered if this fix has held up. I would think that the tank/lines/filter is sending this crud down the line? Are you using good quality gas with cleaners in it ? like techron? up here in canada i have asked my wife to run petrocanada fuel in it which has 'tactrol' which is the equivilent of techron in the states.