Riceman

2006 A6 with e38 PCM. Just installed a 427 (L92 based, long tubes and all supporting mods) and can't get the part-throttle AFR to come out right. Once the PCM goes into closed loop, the AFR goes way lean, beyond 18:1. Only way I've been able to fix it is to go into open loop. No VE table, low freq MAF table does nothing. Once the condition sets, fuel trims pull upwards of 20% fuel. O2 sensor voltage starts "cycling" or switching going from 900+ mv to around 50 mv, just cycling.

This could be caused by the long tubes and the cam overlap, it would almost explain the "cycling" condition. Any way to tune for an O2 sensor delay in the E38?

Files (tune and log) can be found here http://www.hptuners.com/forum/showthread.php?t=16094

0ZO6PARTS

I am going to guess you have no cats and no rear o2 sensors installed as well as all the codes turned off for the rear 02 sensors.

If so,turn all that back on and install rear o2 sensors.


If the above is not the case disregard what I said.

Andy

Riceman

That is the case, and I can do those things. Curious though... How can this cause my condition? Anything special I need to do after doing those things?

Tuner@Straightline

I looked at your log file. . .but no wideband data was recorded, which makes things difficult, if you PM me your email address, I'll send you a config that might help.

Riceman

Sent! Again, I appreciate any suggestions you might have.

Wideband data wasn't logged, wideband used was the dynojet piece and isn't connected to that HP-Tuners setup.

For reference, ranges were very dependent of whether it was in closed or open loop. In open loop, it was stead in 12.5:1 and 14.5:1 off-idle at cruise speeds (on dyno) and in park. When allowed to go into closed loop, it pulled around 20% fuel and was leaner than 18:1 regardless of condition (park, idle, cruise, etc). We never went higher than 3K RPM or so, I'm pretty sure we won't have much issue with PE mode or WOT as open loop tuning is pretty responsive.

0ZO6PARTS

After you try the above,I will go into why it does this,Tuning is learned and not tought.

Keep us posted.

Andy

Riceman

OK, tried a few things tonight including re-enabling the rear O2's. Same results, though we did get some more information.

This time we marked conditions at specific timestamps, and left the fuel trims enabled and working as they should. Other things we tried were adding more spark at idle and off-idle, messing with the lo-freq table a bit, re-connecting the rear O2's and enabling the associated codes. Tried a lot of things, the final thing was placing the wideband directly into the tailpipe instead of in the probe. It yielded results a bit different than expected. The Cam overlap appears to have a pretty big effect on the trims as every pulse is read and is definitely causing the O2's to switch as seen in the logs. We did some logging with the rear O2's and they showed the exact same thing. When we placed the wideband into the tailpipe, we could see the exhaust pulses going from 18:1 to 15-16:1, then back and forth, this coinciding with the O2's in-pipe switching. If there was a way to buffer that switching, like the O2 integrator delay I've read about but doesn't seem to be in the E38, we might have a winner.

Perhaps our wideband probe isn't yielding the readings we need, don't know.

Now, Andy, why would the rear O2's cause this condition? In my old '05 GTO I had them out and disabled, and this didn't crop up. Something new with the E38?

ninja edit: new tune file and logs are here http://www.hptuners.com/forum/showthread.php?t=16094