Fuelling Problems (on the Dyno)

[Plums]

Tuned a couple of cars yesterday (03 model Holden Utes) and ran into a problem. To set the scene, these two Utes are almost identical, (autos with full exhausts) and amazingly they BOTH put out 203 KW's with the standard tune. After some PE and IGN tweaking, one of them made 236.5 with nice flat AFR's, (very impressed with that). The second one was a different story. I put the exact same tune (236KW tune) into this Ute, the fuelling was never consistent making it very hard to tune, but the big problem was at the top. The AFR would get rich at around 5 grand, and I couldn't tune it out.
All of my programs had the COT turned off, but checking the logged data shows the LTFT's going positive at 5 grand.

Any help would be great...

By the way, the problem child only put out 215.7KW's

Thanks,

Plums...

[Plums]

Anyone have any ideas on this one???

[Chris@HPTuners]

sounds like you need to work on the LTFT's in cell 15 is my guess. Try resetting fuel trims just before the run and see if the problem goes away.

[jimmyblue]

Why would LTFTs suddenly change at WOT, -during-
WOT? That's a new one.

Wonder if maybe the second run put you afoul of
some ECT-based enrichment?

I was playing on the highway last night and found
that COT can be tripped at sub-WOT, and persist for
quite a while (I have mine still enabled, but with low
and unique enrichment min/max values - these came
on @ max during a 75%-TPS pull and hung around for
a -long- time afterward at the minimum setting (1.01).

[mustbbrent]

To reset the fuel trims, do we have to get out of the vehicle and find the PCM fuses or will the SCANNER control option actually reset fuel trims inside the vehicle's VCM? Sorry for such a stupid question. Everytime I feel like I have a handle on what I am doing, I look and find myself in the dark again. :P Thanks.

sounds like you need to work on the LTFT's in cell 15 is my guess. Try resetting fuel trims just before the run and see if the problem goes away.

[Chris@HPTuners]

Why would LTFTs suddenly change at WOT, -during-
WOT? That's a new one.

many cars will drop into cell 15 at high RPM on the dyno, it could be that this trim is positive. A quick look at the scanner will verify.

Chris...

[Chris@HPTuners]

To reset the fuel trims, do we have to get out of the vehicle and find the PCM fuses or will the SCANNER control option actually reset fuel trims inside the vehicle's VCM? Sorry for such a stupid question. Everytime I feel like I have a handle on what I am doing, I look and find myself in the dark again. :P Thanks.

reset fuel trims via the scanner "VCM Control" option(under the Tools menu)