6.0 Loss of power

Matthew Ernst · March 16, 2020

New member here from West Bend, WI. I recently got rid of an 06 Yukon XL Denali and got a 2002 2500HD. When I purchased the truck it was getting poor fuel mileage. Roughly 250 miles to a tank of gas. I started checking it out and the fuel pressure regulator was bad. Vacuum line was full of gas. Went to the Autoparts store and purchased a new one and replaced it. Fuel mileage went up, not much but better. Since then the truck has been gutless. Is this how the truck is suppose to be or do I have another problem?

2002 Chevy 2500HD CCSB with 6.0 gas. 4:10 gear ratio. 265's.

davester · March 16, 2020

There's lots of things to do/check:

-do a fuel-pressure check on the fuel rail. You should get about 60 psi at the rail, both when idling and when you rev up the engine to, say 3k. It may drop briefly, but should quickly return to full pressure

-there's a fuel filter along the inside of the frame rail under the driver's seat, you may want to replace it

-check the exhaust manifolds for broken off bolts into the heads, as well as to the downpipes. If they are broken, replace them all (as well as the manifold gasket). The rear ones will be difficult to get out, but you can get clamps to replace the bolts that go into other, unused holes in the head to clamp the manifold to the head

-clean the MAF sensor with MAF sensor cleaner, and the inside of the throttle body with throttle body cleaner

-look at the air filter and see if it needs replacing

-spray something around the edges of the intake manifold where it bolts to the heads, to see if the gaskets leak.

-get a code reader, and read codes from the engine (at the very least, it would be better to get codes from all the computers in the truck), as there can be codes even with the CEL is off

Also, look at the brake lines, as they tend to rust out. Look along the frame rail from the driver's side front wheel to the abs controller under the cab, they rust out really bad along there, as well as the rear line along the frame rail above the fuel tank (which is difficult to examine).

Matthew Ernst · March 16, 2020

I guess I should have mentioned I did an oil change, air, cabin and fuel filters as well. All my brake lines have been replaced. There are no active or history codes. I do have broken manifold bolts. I know they are common on these motors. I've replaced/extracted more than you know. I was going to check the throttle body as well as the MAF sensor. It's just weird because I noticed the difference once I replaced the fuel pressure regulator. I will check the fuel pressure tomorrow and report.

I

Edited March 16, 2020 by Matthew Ernst

CamGTP · March 16, 2020

How many miles on the truck?

If you have a scanner, watch the fuel trims. See if they are more overly positive or negative.

If the front o2 sensors are original, may be worth replacing with new delco/denso parts. All in all the truck is still a heavy pig so getting more than 13-14mpg may be tough. But with the fuel tank size getting 300+ miles to a tank should be possible for sure.

Matthew Ernst · March 16, 2020

The truck has 210k on it. I'm not worried about the fuel mileage but my denali had a 34 gallon tank and I was able to get almost 360 miles a tank. I have a 26 gallon tank now and I'm struggling to get 300 miles a tank. Again, I'm not worried about the mileage more so the loss of power. Not sure on the age of the o2 sensors, but by the looks of them they are not original.

Matthew Ernst · March 18, 2020

Really? Nobody has any input?

riverbanks · March 18, 2020

How did the fuel pressure test go?#'s

CamGTP · March 19, 2020

I'm a hands on type for most things, I can only arm chair mechanic so well when I can't see or feel what the truck is doing.

A stock 3/4 ton from 2002 is going to kinda be a sled, they are very heavy and the factory programming is made for emissions and longevity for towing. I've helped tune many in the past and that is where there get the best results for get up and go. So long as everything is in proper working order in the first place.

davester · March 19, 2020

...and fix the exhaust manifold bolts..

The ecm depends on data from a bunch of sensors to run the engine, and when one or more sensors is giving false data, all bets are off as to how the truck will run (and broken bolts can cause exhaust leak, where fresh air gets sucked in, making the O2 sensors read that the mixture is lean, so the ecm dumps fuel into the engine). And if the fuel pressure is off, that makes the problem worse, as the injectors then don't spray properly.