I have a 2001 Chevy Express van 2WD with the 4.3 V6 with around 100,000 miles. The problem I am having is after the van has been running for about 45 min or more continuously with the AC on, at normal throttle it runs fine but when you do WOT it will skip and misfire and make loud noises from under the hood. I have replaced plugs, plug wires, distributer cap and button and also the air filter and fuel filter. But if you turn the van off then let it sit for a couple minutes or so it will run just fine but for some reason it will only do it when it has been running and idling with AC on for 30 minutes or longer and you go up the road and it will act up again. Well it is showing a P0440 code which is a Evap code but would this have anything to do with how it acts at WOT? Please let me know something...

 

When you fill your gas tank, do you fill up to even change or overfill to the nearest dollar?

A smell of raw gas after you drive away from the pump would be an indicator.

Possibly your Evap Cannister is flooded with gas and it's having an effect on gas flow at WOT???

 

Well it will only act up after it has been running for 30 minutes or more conituously. Could it be a sensor or an ECU problem?

 

Wouldn't hurt to check if your EGR valve is clogged.

 

All of this has been checked...i'm so frustrated with this van. I have no idea what it could be. I also had the ignition module checked and its good. So I'm going back to the drawing board and see if anything has been over looked...

 

Problem solved!!!! The exhaust manifolds where they bolt up to the Y-Pipe the metal donut gaskets were bad causing exhaust to heat up under the hood really bad and causing the ignition module to get too hot and mis-fire at high rpm's.