Power loss on hills when loaded

mxhowes · June 1, 2005

'96 GMC Z 71 5.7 111,000 miles

This truck runs fine in daily driving but when I get on a long trip and pull some hills it starts acting up. (I will be carrying a light weight 1500 lb pop top camper and pulling a 1200 lb motorcycle trailer).

You will first notice a slight cough on the level interstate when you try to give it a little more gas at the bottom of a hill. After several miles up the hill in 3rd (22-2500RPM) the check engine light (MIL) will come on. At this point SOMETIMES the truck will keep running good but sometimes it will abruptly loose power and will start to slow down. The truck will never quit, you just loose speed, maybe go down to second and you can feel it catching every once in awhile, gaining power, then slowing down again. Once you crest the hill it may run fine for the rest of the trip (except for a cough every once in awhile) or mess up on the next hill.

It will throw two codes (P0131 & P0151) that show low O2 sensor readings.

It has a new fuel filter.

Jim

AG Bill 05 Z71 · June 2, 2005

Sounds like a plugged fuel filter.. recommend you check your filter or replace it....

MrQuadrasteer · June 2, 2005

Good place to start, Bill.

When was the last tune-up ?? You might also clean your maf, check your filter, the basics first.

What temp is it at when this happens- any warmer than normal ??

Hotwire · June 2, 2005

another thing that comes to mind is the catalytic converters. seems the 96-98 years weren't that good. the catalyst inside the housing breaks apart and starts clogging the exhaust flow. hop under your truck while it's off and cold, pop the cats and listen to see if you hear a rattle.

when's the last time you ran injector cleaner through? I recommend w/ the vortec motors to at least put a bottle through at every oil change.

good luck.

mxhowes · June 2, 2005

First to answer some of the suggestions.

20K on Plugs, wires, cap etc

4K on Fuel Filter

Injector cleaner about every 3K

There is nothing rattling around in the Cats

Temp around 200 when pulling the hills.

EGR looks clean, no carbon build up

I put together a fuel pressure gage. Key on 64 lbs, Idle 54 lbs & jumps to ~ 57 when you rev it.

In thinking back on when this happens it seams to be always within 50 miles of filling up the tank (I never top it off, but do fill it till it clicks off) could it have something to do wth the charcoal canister? Is there someway of checking this?

Jim