Ben Ayres

I have a 99 Monte Carlo with a 3.1. I have some problems and wondering if anyone has the same problems.

I have codes for Engine misfire, EGR Valve, Evap leak, and fuel level sensing circuit high.

Would an EGR valve malfunction cause the misfire? I was gonna diagnose the the fuel level sensor code and was wondering if anyone else ran in this code. My main question is about the misfire.

Thanks in advance for the help!!

tech2

post the codes that have set and then I could give an accurate response.

Ben Ayres

I will have to wait until I get to Work tomorrow. Wrote them down but left them in my tool box

Ben Ayres

Codes I have are

P0300
P0401
P0404
P0440
P0463
P1404

tech2

its not impossible for egr issues to cause misfires codes. Usually, the most common issue is a rough idle.


What are the operating conditions when the misfires are occurring? Idling, cruise, wot, hot/cold?


3 codes are egr so remove it and see if its clogged, stuck.

Ben Ayres

WOT when hot

tech2

its possible that the misfire is due to unwanted egr flow at wot. the egr should be commanded closed at wot. The p1404 will set when the pcm detects open egr position when its commanded closed.

Ben Ayres

alright thanks. I'm gonna get it off and try cleaning it

Ben Ayres

Pulled off the EGR valve and found the EGR port was plugged. Cleaned out the passage way and cleared the codes and so far the light hasn't came back on!!