6.0 doing some crazy things

[Weldinchevys]

Hi everyone. I drive a 04 GMC Sierra 2500HD 2wd with the 6.0 has engine. I’m very machanicily inclined, but I’m scratching my head on this. 

 

It runs great, idles a litttle rough but not bad. My scanner showed an engine misfire of 7 times on cylinder 7 with 3 minutes of run time at 2500 rpm.  Now to the problem. When I am driving down the road it runs great gets up to speed well. When cruising, I try to down shift to accelerate, engine revs to 3000 rpm, and falls on its face. Rpms start dropping, speed decreases. As soon as I let off the pedal, it shifts and gets back up to speed. I’m not sure if the misfire could be making the engine do this. I’ve had similar problems with another truck, ended up being the cat converters. I have deleted them on this truck to attempt to fix this issue. New TPS, new plugs and wires. Does throw a code for 02 sensor every so often. But only comes on once in a while. 

 I’m scratching my head on this one. Any help would be greatly appriated. 

[davester]

What do you mean by "deleted them (cat converters)"?  You just removed them or did you also get the truck retuned afterwards, with a tune that is coded for the truck not having them.

 

There is a specific, fairly simple test for if the cats are causing a problem (you measure the pressure at the upstream O2 sensor), and if it's more than X psi, then the cats are plugged.

 

Anyway, it needs a tune specifically for having the cats deleted.

 

Once that's done, I would go for looking at live data on an odbii code scanner, to see what the ecm is doing when this problem happens.

[Weldinchevys]

I just removed them and did not have it tuned for that. I replaced coil pack for cylinder 7 and no more rough idle. The truck and the no return fuel system, no filter or pressure regulator, all in sending unit. Wounder if either could be going bad, going to check pressure tomorrow and will repost with results of test.