I'm getting a set of long tube headers very soon and I'm going to run a heated O2 sensor just in case. My van originally had a heated O2 sensor so the 3 wire harness is there.

I switched to a 1-wire because it would idle horribly if I let it sit to warm up. If I drove it, it seemed ok. But I think there is some issure where the O2 sensor is warm and the ECM is trying to go into closed loop.

Maybe I should try adjusting the closed/open loop timer? I don't want to jump right into this because the idle oscillates wildly from 800-1200 rpm...only with the heated sensor. AND it only does that if I let it sit and warm up. If I drive it then it seems fine.

Anyone with a 7747 have this kind of problem?..any ideas?

 

Yes, you should "play" with the timers for "cold start, warm start and hot start". I find that my O2 sensor is ready for "closed loop" really soon on a hot restart - but I still like it to run for about 30 seconds.

Conversely, I found that I like a minimum of 180 seconds for "cold start" no matter how quick the O2 sensor is working. Part of GM's logic in the timers was to match the ecm entering "closed loop" when the cats are ready to "light". You can continue with this "approach" or develop your own (i.e. go into closed loop sooner, or later).

 

I see there is also two values that have to do with O2 voltage and closed loop.

One is "Go into closed loop upper limit" and the other is "Go into closed loop lower limit".

I'm guessing that when the O2 sensor is cold it is reading .45 mv...right? And it starts swinging when it warms up? So once it crosses these values it goes into closed loop if the other things are already met?

Am I close?

 

Your close. Those are the "cross count" boundaries the ECM needs to go over/under to ensure the mixture is "oscillating' properly between rich and lean.

But Iwouldn't play with those. They are more useful if you have Long Tube Headers with a regular O2 sensor which just can quite get warm enough.

I would work with the timer and the "minimum coolant temp". Also, there are temps to determine when to use "cold, warm and hot" start logic. Look at those.

 

Thanks Glenn!!