When I installed a new MAF chip this spring, I did a couple of logs of the a/f ratios.
The chip was very well mapped, slightly rich on spool-up but otherwise almost perfect. I went out yesterday with the intent to fine-tune it. I was quite surprised to see that I was now running seriously rich. Actually off the scales of my WBO2 (richer than 9.6:1). Kind of strange considering that I haven't touched anything since installing the new chip 6monts ago. I spent 30 minutes tuning it to ~11.8:1 at WOT and it called it a day.

The only reason I can think of is that I have a boost leak. The AFR at idle and "normal" driving was OK, but under WOT it was very rich. If I have a boostleak the O2 sensor would keep the AFR at ~14.7, but at WOT the signal from the O2 sensor is ignored and a predetermined MAP on the chip will set the amount of fuel. Does this sound logical?

Anyways, I did pressure test the intake (after turbo) today. I found no apparent leaks. I did notice 2 things though:
1. If I squeeze the line going to the MBC, pressure increases slightly (~1psi).
2. If I squeeze the line to the fuel vapour thingy pressure increases slightly (~2psi).

A few other things I've noticed:
- At idle I see 17.5-18in/hg of vacuum and 14.7:1 AFR. If I disconnect the TPS I see 19+ in/hg of vacuum and ~10.5:1 AFR. Why does the vacuum increase?

- As I apply throttle, just before WOT the car jerks slightly. I'm guessing this is where the DME goes from closed loop to open loop. Why the jerk?

 

doh! I just saw this on the email list, sent an answer there...

Russell

 

Hi Eivind, Something has changed to get the different AFR. The software does not change, now to figure out what could it be.

Not in any order, check the followings:
- Check for vacuum/pressure leaks (You already did)
- Check the TPS
- Check Engine Temp Sensor.
- Is the FQS and Fuel pressure the same as before (3bar is what you should be running).

- Clean MAF connector to harness.
- Make sure the SMT6 has the correct data (Global Settings --->Analog" values...
- - If running an adjustable FPR, if there is a way to monitor the fuel pressure under load, great. If not try a 3bar FPR.

Hopefully you did a previous Data Log with the PB. Comparing old data log to what you are getting now might be of help.

 

Thanks John.
I'll have a look tomorrow.

I do all my logging with the Zeitronix. I did some logs with the PB last year, but the O2 signal doesn't register. I've gone over the wiring 3 times, and everything appears to be where it should be. I also get a reading on the AengTemp, but you said the value is so low that it will not make any difference.
If the O2 sensor is shot, I shouldn't get the part-throttle readings I'm getting, right? (~14.7:1).

 

Eivind, make sure you have "1" in the Eng Column. The O2 sensor does not affect WOT.

 

Eng column shows "1". Global settings --> fuel lower limit says 0V. If I change it to 0.3V apply and save and check the settings again it still says 0V.

 

Eivind, email me the map, I'll look at it. Let's continue this off-line.