The PFC, the air pump, and the O2 sensor...
 

Hey guys -

I'm doing some experimenting this week with my car and a midpipe. Long term, I'd like to have a custom high-flow cat done on the midpipe for stink control, if I can find one that can live without the air pump, that would be a bonus.

Anyhow, the stock ECU uses the O2 sensor for feedback for idle mixture and low load/cruise mixture. With the airpump not running on the stock ECU (unplugged, fuse blown, etc.) the car idles slightly lower and rougher, throttle tip-in is lousy, you lose some idle vacuum, etc. Basically it's not optimal.

From what I can tell, the stock ECU is compensating for the airpump air injected in the manifold at low load/idle for it's O2 sensor readings.

Does the PFC "compensate" for the air pump as well? If the PFC did the idle learn on the car with the airpump not connected, would it learn "right"?

Also, I currently have the midpipe on the car and the airpump hooked up and working with the PFC. The air pipe to the main cat is still there. I haven't heard the air pump air coming out of the pipe, but it may just be hard to hear or something. I would assume the PFC properly handles split air? That's just a curiosity thing, though :).

Anyhow, just wondering if anyone has any thoughts on the topic.

Thanks,
Dale

It does, but it shuts the air pump off at 2500 rpm, instead of 3200 rpm like the stock ecu does. Which means that it almost never runs....:) To pass my smog test at 25 mph, the tech had to shift into 3rd to keep the rpm below 2500 rpm.

The PFC can not control the idle/cruise AFR corretly without the airpump, but it has the abilty to TURN IT OFF. Thus you then have direct control of idle and cruise fuel.

Gotcha. Kinda goofy that it can't re-learn the idle and whatnot without the airpump.

Thanks!
Dale

there's an option to ignore the O2 sensor completely :)

Dale, I experienced all the same symptoms... I turned the 02 feedback off on the PFC, and it litterally corrected immediately... though mine was a result of a bad 02 sensor, not a missing airpump (though there's no cat on my car).

Interesting. The main cat is going back on this weekend - the midpipe experiment didn't pass the wife "stinky" test :). I'm eventually gonna do a custom high-flow cat or something, and I'm looking into running one without an airpump - that's for another forum, though :).

Thanks guys,
Dale

Dale contact M104-AMG. He helped me out with some info on his custom metallic cat and resonator. It was real nice. He used the MP he had and had a met. cat put in and a resonator and new O2. PM him, I am sure he could point you in the right direction on this. I am doing this soon, so I am extremely interested in what you find out. I was thinking of doing the Bonez high flow from the 7store. Jason said he would do a group buy on them.

Just buy a metal core cat and have it added to a midpipe. The cats are around $150. I'm sure the exhaust fabricator can rig up a tube for the air pump pretty quick.