Inconistent fuelling @ WOT.

[Plums]

Had the Ute on the Dyno today to see what's happening with AFR's and Power.
The stock Program was actually pretty good, returning 183 KW with the AFR going no lower than 12.

Tried a few of my programs but struck a problem. The first run of any of the programs was pretty good, with reasonably flat AFR's, (LTFT's pegged at zero). Any subsequent run resulted in increasingly rich mixtures (and I mean rich, down to 10) from around 4400 rpm and up. The strange part is the LTFT's were still pegged at zero. This is really obvious on the playback log, even though LTFT's are zero, you can see the injector banks stepping up, (adding more fuel in large steps as rpm increases from around 4400 up).

This makes it extremely hard to tune because the computer seems to add fuel whenever it likes, (after the first run which is always good).

On a positive note I got power up to 197 KW, (the Ute is standard except for the MAF pipe) which is pretty reasonable for the short time spent on the dyno and the fuelling problems I had to chase.

Any ideas???

I can send my log file if that will help...

HELP...

Cheers,

Plums...

[Chris@HPTuners]

moved to the V8 Engine Tuning section.

sounds like catalytic converter protection (COT) to me.

[Plums]

Thanks Chris!

It'd be nice if I could spell too, (inconsistent)...

After many Bourbons tonight I'd actually thought of COT. The dyno shed temp was up around 35 deg, with no airflow around the car except for the rad cooling fan. This, combined with the fact that the AFR gets worse after the first run, (and continues to go down hill from there) got me thinking COT.
If only I'd known this today whilst chasing my tail like a mongrel dog.
Next dyno session, COT off...

Has anyone experienced this problem, or was I just too stupid to think to turn it off?

Plums...

[jimmyblue]

I have knocked my COT max enrichment down to 1.05
(from the 1.14 stock?). I don't think road / shed airflow
is something the PCM comprehends, I think it's just
calculating an exhaust gas temp by O2 sensor and/or
commanded AFR, and guesstimating the cat temp.

But this is just "preventive medicine" against an action
I haven't run into yet (there being few opportunities
to spend more than seconds wide open, in my usual
environs).

[Chris@HPTuners]

most common mod is to disable it completely or increase the temps.

The cat temp calculation is quite complex and includes a lot of lookups vs. RPM, MPH, Airflow, Spark, etc. in the end it is a best guess by the PCM and actually doens't take into account the O2 sensors at all... :-/