WOT AFR's

[DJJUT]

Can anybody explain why that in a WOT run with no knock the desired AFR's are lower than what I have requested in the WOT fuelling tables? I can take two seperate runs and the desired AFR's can be different to each other. Probably missing something simple so hopefully somebody can point me in the right direction.

[mituc]

The presence of knock retard is not the only thing that will make the ECU dump more fuel. There can be a different other things which I don't know exactly but as far as I know it may be one of the following (or combination of them):
- approaching a limit or exceeding it (MAP, load);
- high BAT or high ECT;
...and so on.

Also take a look and see if the desired AFRs are close to the OL part throttle table values. if for some reason the ECU will start closing the throttle plate a bit it may use the part throttle tables despite de 100% APP.

[DJJUT]

I believe it has something to do with ECT but the only fuel table relating to this is ECT vs Fuel Pressure so unless there is a table not available I am a bit stumped. Running meth BAT's are okay and even with no meth the issue still exists.

[mituc]

I kind of have the same problem and frankly I never bothered... As long as the desired and actual were so close I thought it's fine. However, the desired AFR values were like 10.3 instead of 10.6 at WOT and only at very high RPM (above 6300, say), so the variation was not that big. I noticed the problem is more obvious when the ambient temperatures are higher, but the ECT temps though are around the same as the thermostat takes care of that.
Maybe it worth asking this question to Steve, or the gearheads on the MSF. It's definitely something like I said initially and yes, it's controller by some tables we don't have access to which I wouldn't touch even if we had access, but the idea is to at least understand what's going on.

[skiptownmcat]

Just to add to this, I get commanded afr's of 14.2 at idle and the only way to stop it is to reflash the tune.

[mituc]

Wow! That's something I did not notice on my car at idle, no matter the outside temperatures (+42C or -22C - I monitored in both conditions).
Does this happen with the AC off as well? Maybe the AC clutch is worn and puts too much strain on the engine (what's the load average at idle?).

[skiptownmcat]

Nothing like that, AC on or off makes no difference.
I do however have a small exhaust leak from the turbo to down pipe. Could it be that the ecu logic starts to command richer afr to even out the lambda sensor readings??

[mituc]

Most probably...