I had posted on here about 2 weeks ago with some DM logs about my car acting up, but didnt get any responses. But in that post I mentioned it was switching to open loop real quick and then back to closed loop .

I was just wondering what causes the PCM to do that? After the car gets into Closed loop, what tells the pcm it needs to go back to open loop for a sec, then right back to closed loop?

I noticed when it does this it resets the sterms to 128 , then they start to fall some.

Just wondering

Jason

 

After doing some researching a couple of weeks ago, I came across something that said if your 02's cool down enough that it can kick the car back into open loop until they heat up again.

 

THink headers and no cat would cause this condition? Since I added headers and heads my car has ben acting up. Actually it took it about 1.5 weeks to start up. Good (but used) O2s fixed it up for about the same amount of time. You think too much fuel would prevent them from heating up correctly too?? If so I think I really am looking at a tuning issue. my blms are 108 anyways so .

Thanks for the info

Jason

 

Ok, I'm relatively new to tuning, so bear with me. If your BLM's are at 108, then that's on the rich side if I'm right. Too much fuel, going off of what I know, would run cooler than not enough fuel, so in reference to your question, it could possibly be the culprit, but AFAIK, 108 on the BLM's isn't too bad.

One thought I had, when you put in the Long Tubes, you had to use entensions on the O2 sensors, right? Did you use a repro extention, or did you go the cut and splice route. I believe that the cut and splice route on O2 wiring was a no-no, so that could possibly be another culprit.

I know that an extended amount of idle time will allow a car to cool down sufficiently to throw it into open loop, as I have watched my 93 do. That said, my 93 doesn't have heated O2's, so it could be a various 93 anomely.

One other note, go buy brand new O2 sensors. I would NEVER throw a used O2 sensor into a car. Too many possiblities. That could be the end all to the problem right there.

Tuning Guru's: If anything I've said is a completel crock of you know what, please educate me.

 

Yeah I used O2 extensions from Jet Hot.

Anyone think maybe an opti problem would cause my car to run rich like that and the PCM to subtract fuel?? (Ie makeing my BLMs 108, and my sterms always dropping low?)

But I would think missfires would throw more air into the exhaust and thus the 02s would think lean, and try to add fuel??

Jason

 

108 BLM's are "bad"... that means that the PCM has continued to pull fuel and reduced the BLM's to 108, they are "bottomed out" (that's as low as they can go), and it still hasn't corrected the problem. Appears GM limits the BLM's to the range of 108 (-15%) to 160 (+25%), so if you reach those extremes you will get a code. You should think in terms of +/- 5% on BLM's (121-135).

Find the reason the PCM "thinks" the engine is running too rich and is trying to make the corrections.

At 108, yes, you have tuning issues. Are all the BLM cells 108, on both sides, or just certain cells?

What is the coolant temp doing when its switching back and forth between open and closed loop? I'd suspect the O2 sensor temp as a problem, but coolant temp is also a possibility.

 

Injuneer,

the logs I had where made with just the car idling. We did a test drive but I dont think it switched back and forth then, although when it did stumble it did drop the sterms to 80 something.

Both sides are at 108

coolant temp when it switches is 177.4 degrees F. and stays there as i switches back to closed loop.

Thanks guys for your input

Jason