"84 Crossfire Vette, Renegade, 90# Injectors, programmable ECM from Dynamic EFI, other mods... - Wrestling with heated NB O2 readings. Initial problem O2 was reading constant 459 MV's, replaced it with a new heated Bosch and got constant readings at about 60 Mv's. Found what I believe was an intermittent short in the ECM connection wire soldered it and tested continuity got 1/2 ohm so I assume it was a good fix. Still wasn't getting any movement . Replaced the Bosch with a used AC Delco AFS74 which bench test ok (propane & ohm meter) and that one also isn't reading. It's stuck this time at near 1000 MV's. Crazy. Have a WB that is working so I can compare another reason why I know when NB readings are bad.. Anyway, anyone have a clue what might be going on here ? ECM issue? Should I run a new ECM wire? Thanks.

Getting tired of jacking the car and playing with the sensor, as you might expect.

 

The O2 sensor circuit has a dedicated ground point from one of the ECU pins that I believe runs to one of the studs on the back of the cylinder heads (on the F body.... Vette.... IDK). Check that you have a solid ground for it. Should be in your diagrams somewhere.

GD

 

Thanks - will do...

 

Looked and found the O2 ECM ground - checked OK. After that for kicks I played back my last data log and sure enough at idle I was getting a near constant 986 MVs as the WB is telling me my AFR is in the high 13's. Duh, the NB was giving me an accurate read cuz I'm idling a bit rich. My head was wrapped around the other two sensors that wouldn't budge off lower readings and I assumed this was happening again but stuck at a high reading. Anyway continuing to watch the diagnostics and examining the log dump I found the NB doing exactly what it's supposed to do - when the WB AFR cracked 15's the NB responded with voltage drops, consistently. So back to the tune finessing now that I know both O2's are functioning - just need to figure out what to do with "em.