Hi All,

First, I want to say this is a new problem. I have owned this truck for over 7 years with the same travel trailer setup, and this problem never happened before this summer. Please don't recommend a tuner. I am fully aware lower end power sucks with these trucks, but this is something more than that.

I am having some issues with my 2005 Suburban Z71, 5.3L, flex fuel compatible. Seems to be only happening under towing conditions, can't verify if it does it under heavy load without towing (like a bed full of crap would show on a pick up). Tow mode on / off doesn't matter. Power is horrible at take off, especially on uphill surfaces. I actually got stuck going up a mountain hill over the summer. Had to use 4-low to get up the hill. Once I hit 2500-3000 rpms, it starts getting power back. There is a rattle-ish noise at high RPMs, but that doesn't seem to set off the knock sensors. Nothing noticed at low rpms. Scanner shows the computer is massively retarding the engine during the times of power loss with any throttle over 1/3 under 2500 rpms. Occasionally, it will set the knock sensor low voltage codes. Knock sensors have been replaced several times, along with intake manifold gaskets and the sensor harness. Not much is showing up on the scanner that doesn't look normal, except the engine retard. I have done the crank recalibration as well. Sensors and harness ohm out in spec. Tried premium fuel, nothing changes. No vacuum leaks, tested with smoke machine. No aftermarket modifications besides upgraded brakes. I thought maybe a ground somewhere, but they all are connected and ohm out nicely.

Anyone run into an issue like this before? I feel like there is an underlying issue that only presents itself under heavy load, but I can't seem to pin point it. I really want this fixed before next camping season begins. Can't afford another vehicle either. Pulling my hair out on this one. I was a mechanic for 13 years, never had one of these GM engines continue to do this. I unfortunately don't have any access to Identifix / AllData / Mitchell anymore either. Any help would be appreciated.

 

check for carbon buildup in the engine. Is your tailpipe sooty?

 

Tailpipe is clean, no soot. I haven't scoped internally yet to check for carbon build up. I had the one head off a few years ago to replace the lifters, looked pretty clean then. It's been probably 15k miles since then, so it could be built-up by now though.