Truck loses power at WOT and acts like fuel delivery is poor

[SDavis]

first the basics: 2001 yukon xl 1500 2 wheel drive 5.3l with 144k

Problem Codes p171,p174,p131,p151

When first started in the AM I experience a very rough idle for about 20 seconds. After this the truck runs relatively fine but I suspect not all the power is there. A sure way to really get in a mess is to put it under heavy acceleration. At WOT the truck will acelerate hard then fall on its face and I cannot get it to accelerate if i give more than 10 percent throttle. If I give it any more throttle the truck trys to die. I wind up doing 10 mph to get out of the way. She will idle fine though. Usually a rest or diconnect the battery will return the truck to its version of normal. If I baby it around I usually do not expirience any issues other than rough start.

Replaced Fuel Filter, MAF sensor, Air filter, Cleaned the Throttle body (this cured an additional problem of dying an low idle) Side note: i was not able to remove the TPS while cleaning TB, replaced PCV valve, sprayed all around the intake and checked for vacuum leaks with starting fluid.

 

[bahollis]

Fuel pump? When you first go to start up, and turn the key to AUX do you hear the fuel pump whine?

BH

 

[SDavis]

Yes. I can hear it kick on for about 5 seconds. I have not tested fuel preassure but there seems to be plenty when i depress the needle on the fuel rail on top of the motor. My brother also noticed the exhaust temp is increadibly hot. It burned his hands when he held them a foot from the tailpipe as the motor was running at its worst. I checked the read out on the O2 sensors as well, seems to be fuctioning correctly at an idle. On both banks: O2 senson 1 rapidly fluctuating from .1 to .8 and Sensor 2 averaging a .6 with far less fluctuation (.5-.7) Short term trim >8% Long Term steady 25%. This all at idle. I created a vacuum leak and it did what was expected. Lean for 20 seconds or so and balenced right back to previous numbers. It seems to get seriously lean when expiriencing problems (all at .001-.005) But I admit I dont really know squat about this. Just youtube video searches!

 

[BubZX]

you mentioned about the exhaust being hot. ur cats not glogged is it?

 

[SDavis]

not shur how to tell.... ?