SSkeet

I was tuning an otherwise bone stock 02 fbody rear mount turbo car yesterday and the AFR was high 10's to start out and off the scale rich after 5200. So I scaled entire table up some and got it to 11.4 across the board, but then at 5200 it still fell off very FAT.

I've noticed this happen before with the CAT Overtemp still enabled. In the past I have turned it off and then was able to bring up the AFR to the desired level.

So I turned CAT Overtemp Protection OFF and went on to tune. I scaled the 5200-6000 cells in PE by .99. This brought the AFR up a tad from say 10.3 to 10.4. So then I scaled 5200-6000 cells by .98 and BAM 5200-6000 AFR jumped to 15:1 !!!!!

I tried the same thing with the Overtemp Protection still ON and it did the same thing. I would get the AFR after 5200 to about 10.5 and then ANY SMALL CHANGE (could be 1-2%) WOULD SHOOT THE AFR WAY LEAN!

Its obviously not a fuel delivery problem, we have 42lb injectors in the car and the first pull showed 10's across the board after 5200, so its definately able to deliver plenty of fuel.

Any ideas on this? Strange stuff!
I was thining the overtemp protection was sometimes activating and sometimes not, but im not sure if that would cause this....

SSkeet

no one has any idea?

foff667

iTrader: (2)

have you logged commanded a/f?

gameover

check you openloop fuel table, the PCM uses the richer of the PE and this table when in openloop. The table usually goes richer around 100degC coolant temp. You may be in a different coolant temp range for this table when you are tuning hence you are seeing moving commanded AFR. In anycase, if your PE values are less than this table the PE value is being ignored.

Chris...