Joeboat84

Ok the facts of the van are -
2002 Astro 4wd - 4.3 v6

The codes - p0101 MAF, p0300 Rdm Missfire, somtimes p0301 cyl 1 missfire.

Details - New plugs and wires, New Cap and Rotor - Fuel pressure 57-62 while acting up

What happens - Driving the van up a hill (load on motor) it begins to missfire to the point of having no power. Usually i get a p0101 and p0300, and somtimes the cyl 1. I tried unplugging the MAF to have the computer run in a default mode. No change, still missfires under a load.

Any help at all would be great! I'm at a complete stall on this van, and need to get it fixed. Thanks!

EinST

Welcome to the forum. One scenario is restricted exhaust, either going through the catalytic converter or sometimes downstream of it. When the back pressure builds up, you'll get misfires and even P0101 (illogical MAF input as far as the PCM is concerned). Measure the exhaust back pressure at the pre-catalyist socket and then post-catalyst. You may find a difference (even 1-2 psi at ~2,000 rpm is significant here).

johntaps

Have you recently change any exhaust component? Because engine is designed to run on certain back pressure. If it is beyond that limit, engine would misfires when you accelerate the car. As you mentioned that sometimes it shows p0301 cylinder 1 misfires. I can say that bad catalytic converter makes all cylinders to misfire instead of one.

EinST

That's the kind of empty post I'm beginning to expect from you. Maybe you can tell us what this "certain back pressure" is supposed to be in concrete terms (numbers, rpms).

Joeboat84

I havn't changed any exhaust component. When it started it was a random problem. Now its becoming to the point where i can always get it to misfire. I'm not exactly sure how i would measure the backpressure on the exhaust though. Thanks guys

EinST

Check out link Exhaust Backpressure. My preference is to measure at the O2 sensors (pre-catalyst and post-catalyst) and compare the two readings. Be sure to coat the O2 sensor threads with a little anti-seize compound when reinstalling. If this all seems too much trouble, take it to an exhaust shop.