So I've been logging. A few days ago I had a perfect 11.5 under WOT all the way to redline.

I haven't had a change to log for a few days, but I've been noticing that under very heavy throttle and WOT, that my AFR's have dipped lower now...below 10.

How many of you have problems with the fuel maps straying?
I'm guessing because the fuel compensation maps are not correct after you modify the fuel maps.

 

mind sway as well, not that much, but they do... its weather dependant, grade of fuel, everything matters....

 

If you have closed loop boost control (an EBC of some sort) then they really shouldn't stray much at all, however air density, altitude, weather, all have some effect on your tune.. This is why we have these sensors on the car.. and the compensations work fairly well until you have an MBC that doesn't keep boost stable..

With that said, the ECU will compensate for different boost levels somewhat as long as the cells are tuned accordingly.

It will always vary slightly though, this is why most cars have closed loop fuel trims, and why its important not to tune a daily driven car on the ragged edge of AFR or Timing..

 

So my tune is still straying by a considerable amount.
I can log runs in the 11.5 range, and then also in the 10.7, 10.8 range.
It kills me when this car runs into the 10's.

I'm thinking it has to do with my short term fuel trims...that maybe the short term trims affect the open loop map.

Anyone know how to remedy this?

 

Fuel trims should have no impact on your open loop maps..

You need to compare your MAF (airflow) values between the runs where its different, I'd guess that it may be reading differently, either due to different boost levels, or something else. (A boost leak after the MAF can result in the car running richer than expected too)

 

Thanks. I'll check my MAF voltages.

 

The poorly documented lean spool feature does have delays and thresholds in it that produce apparent irregularities.

Generally I find that a tune that is well judged at one point should always be so, and if it isn't you have DIY tuning stuff to give you the privilege of modifying your map over time and getting the feel of a good all round tune.

Some of it does come down to feel and experience over many dozens of cars.