I run an open loop tune with my F/A ratio nailed at 13:1. My exhaust setup consists of Hooker LT headers, mufflex 3" Y pipe and borla catback. What can I expect after installing extensions and turndowns at the collectors instead of the y pipe and catback in terms of F/A?
RG

 

Aren't the O2's not used in "open loop" (closed loop w/ learn disabled)? If they aren't used, then you should be fine because the affect is that the O2's will read lean and keep adding fuel with open headers in closed loop. This is my understanding of what I've read.

 

Not correct. It would run rich at WOT.

While the O2 sensors aren't used for feedback at WOT, what they helped the PCM "learn" is used at WOT. Hence, anything that affects the O2 sensors in closed loop/part throttle operation has the potential to affect the A/F ratio at WOT.

If you run true "open headers" with nothing past the collectors, and the O2 sensors located in the collectors, the backwash of air at low/moderate loads will cause the O2 sensors to report a false lean condition. The PCM, seeing the lean readings from the O2 sensors starts adding fuel in closed loop using the long term fuel corrections (BLM's). Then when you go to WOT and the O2 sensors are ignored, the PCM uses the BLM's from Cell 15 to calculate the fuel, and the mixture ends up too rich (richer than the PCM's PE mode "target" A/F ratio).

The issue is how close are the O2 sensors to the open ends of the exhaust system. If you are using exhaust "extensions" and turndowns, its not likely that any air can backwash to the O2 sensors. The real problem is running fully open headers, with nothing attached to the collectors.

 

So, the PCM is still "learning" from the O2's when the car is in "open loop"? If he unplugged his O2's and could figure out a way to put the a/f reader probe far enough into the header, could he still tune like this and get correct readings? What about a BLM locker? Point is though, you shouldn't run the car with open headers. I'm just trying to pick brains.

 

Scratch the whole thing.... I neglected the "open loop tune".

 

My question was aimed at the fact of opening the exhaust and its effect on the F/A ratio. In theory, if the MAF meter is doing its job properly, the increase in flow (if any) resulting from a better exhaust should not affect the calibrated A/F ratio while running an open loop tune. However, I was wondering if anyone had any experience with that.

 

I would think this would be true. If the MAF see's an increase in air, the computer should compensate and keep the a/f the same.

 

Not trying to hijack, but while were on the subject...and ijuneer is posting.

Im also running an open loop tune, but one of the o2 sensor wires came loose and drug on the ground causing an ses light. The wires are touching i think, havent had time to jack the car up yet.

Will the ses light from the o2 affect the way the motor runs even if it isnt allowed to go into closed loop?

Thanks
James

 

The SES light might be on because you have one unplugged and the other one plugged up. Unplug the other one and both of your voltages will read ~450 mV and the car shouldn't miss a beat. If that doesn't get rid of the light, check the wires and see if they are indeed touching.

 

Im not really involved in cpu tuning but after i got my madz28 tune from Ion, When i opened my elec. cutouts that are attached right on my collectors and ran at WOT it ran really rich and my ses light came on until i let off and closed the cutouts. thought this example may help, however im not sure if my tuning is closed or open loop.

 

If you didnt ask for an open loop tune from MADZ28, you will almost definatly have a closed loop tune like most people

 

From my understanding, if you want to utilize the full potential of cutouts, then you need an "open loop" tune. If your computer is still using your O2's to help with the a/f, then your car will run rich with open header (cut outs). There are tons of threads saying why, if you're interested in the details.