Howdy y'all! New here, but not to wrenching. Let's get straight to the point, shall we?

2001 Monte Carlo SS 3.8 series two with recently redone top end. New UIM LIM and head gaskets. New plugs and wires. New MAP MAF Upstream O2 sensor.

Problem:/After warmed up when the computer switches from closed loop to open loop ( or do I have it backwards?) The fuel trim will randomly shoot to around 20-21 causing super rich condition, which leads to the stall.

I figured it was the O2 sensor, since the voltage doesn't fluctuate when the grim goes high, or when it falls, but there is no code showing up. No CEL, nadda.

Now it won't even start. New plugs and wires. Gets good spark, good fuel pressure. It tries, but will stumble and give a pop from the exhaust. I figure that's because the pipe has a decent small leak, and its sucking air, igniting unburned fuel from the no start.

Yesterday she started but had no power, and ran like utter ***. That's why it got plugs and wires today. The O2 sensor came in today, so I went to pull her up into the garage to change the sensor, after changing the plugs, and wires, but it won't start. The plugs and wires were done the right way, ONE AT A TIME, and the caps are all seated.

Does anyone have a clue? Would a bad or failing crank sensor cause any of these symptoms? I am a small engine guy, mainly two strokes, I can build a sub 100cc engine that will run 75 mph, and I can get eight HP from 5HP Briggs, but his is driving me stupid. I cannot figure this out. I love this car, it has a few of the common issues, the shift to 4 solenoid is gone, the turn signals and yards are finicky, and the clear coat is failing, but I love her, and want to keep her.

If you made it this far, thank you for your time. Thank you in advance, for reading this, and posting some ideas. If you need more information, I can try to get it.

 

I was really hoping someone replied to this....2001 SS same issue. It’s like she’s possessed. Would run GREAT for a stretch of time, then randomly (dangerously) stall. She’d restart when she was ready. Sometimes 5 minutes after stall, sometimes 20. Sometimes a very rough restart. Let her sit for a few days/a week, starts right up no problems could run fine for a week or more then again randomly stalls. Still troubleshooting, testing grounds, wires, voltage, sensors....the standard. Have not been able to pin point the root cause of codes the come up that get fixed and cleared and then a different code comes up .... etc... I’m doing this as time and budget allows. Which is why I was looking for a reply.

 

Ended up being a bad MAP and MAF sensor, both new from the box, both doa. Salvaged one of each from a wrecked Monte and have been on the road since. Save the fact that I am now on my THIRD ****ing transmission. I can't afford a rebuilt, but it's not too bad to get a used one and change it myself. I love this car, except when I am working on it, then I hate her and every engineer that decided to put things where they are. Between the guy that hid the power steering pump against the firewall, and the morons that designed the 4t65e I'm not sure which I hate the most....****em both with a cactus!

 

Try looking at the ignition switch relay that was my problem with stalls