Like the subject says. I'm working on a 427BB thats been EFI'd with a SD 730. Owner installed heated O2 sensor and this sucker still won't stay in closed loop on a regular basis. Every now and then it'l behave and stay in CL but it usually flips back to OL. It sure looks like the O2 MV's get lazy and set the O2 ready bit to 0. Were going to move the bung so that more of the sensor sticks out into the exhaust stream, but I'm having a hard time believing that thats it. Any other ideas? BTW this is the 2nd new Bosch sensor that we've tried.

Any WAG's would be appreciated..

Thanks


Steve

 

You didn't give us enough info. Does it flip back and forth with normal blm's? Does it have a lean or rich code? Does it have a custom prom and what changes were made?

 

There's your answer.
I had 3 bad new ones in a row.
They have a problem with the internal ground in the sensor.

Get a real A/C one.

 

Not throwing a lean or rich code. I've managed to get the VE fairly close with the bits and pieces of CL data that I've been able to capture. Most BLM's are 124 to 134 range. I t just seems like the O2 MV starts hanging around 500 and the cross overs slow down. Sort of like a cold sensor, then boom, the O2 ready bit goes low & trips Open Loop

Thanks for the advice Grump. We'll shoot for a heated AC with a fourth wire for ground. I keep saying it seems like a flakey floating ground type of thing.

I'll post results when I get straightened out