My commanded AFR is changing rich on me!

[Chris81]

I've noticed that at the track (and street) about the middle of 3rd gear and all of 4th my commanded AFR changes from what i've commanded (which is 12.7-13.0) down to commanding 11.77. This is verified by my wideband as well. Why is it doing this and how am I missing this table? I've tuned for years and I have never ran into this.. I've looked through everything I can think of. HELP!

Some background:

2002 Z06 Corvette
Mods: Vararam, ported TB, B&B Bullet catback, my tuning and drag radials.

What is going on?

[rhit_rs]

I had a similar problem with cat protection causing the commanded AFR to drop in a stepped fashion. Does your ecm have this? On the stock solstice LE5 e67 tune it can command up to a .67 reduction factor in afr. I disabled it and ridded myself of the problem.

[Chris81]

I don't see any tables that change AFR, but now that you mention about the Cat Converter I see some tables that have to do with o2 transition times and lean limits under Engine Diagnostics -> Cat Converter Parameters (tables C3201-C3210)

I'm wondering if that might have something to do with it, I guess it might be seeing a lean condition and its adjusting the commanded AFR to cool off the cats.

I need to play with them and see what happens. Or, I guess I can turn off Cat Converter Protection and see if it stops. It would make sense I guess.. i'm used to tuning cars with no cats so I always turn it off.

[joecar]

Hi Chris,

When cat overtemp protection kicks in, the logged commanded AFR does not include the fuel component from COTP.

If you open your log file and your tune file with scantool->tunetool (ST->TT) linking enabled, you can position the scantool cursor on the place where you see richness, and then in the tunetool you can see the operating cells highlighted in the various tables...

To do this, you have to log the same pids as listed on the axes of those tables, and you have to use the same units for those pids between ST and TT, and it makes it easier if you set the TT fueling units to EQ and log both AFR and EQUIVRATIO in the ST.

Post up some log files and your tune file.

[rhit_rs]

Hi Chris,

When cat overtemp protection kicks in, the logged commanded AFR does not include the fuel component from COTP.

Really?? Hmm, it seemed to me it did on the e67 ecm. Perhaps it does on some and not on others...I can post some logs of the effect if you would like. Unfortunately I was not logging cat temp at the time, but I noticed the drops in commanded afr, speculated it was cat protection then disabled the protection. After that, I logged cat temp and no more change in commanded afr even though the temp it would have kicked in at was exceeded.

[joecar]

Oh, Chris has a Gen III PCM which doesn't include COTP in the commanded AFR...

I don't know what the E67/E38 does with COTP.

[rhit_rs]

Oh, Chris has a Gen III PCM which doesn't include COTP in the commanded AFR...

I don't know what the E67/E38 does with COTP.

Oh, okay. For the record I'm pretty sure the E67 does.

Well, it must not be COTP if the commanded AFRs are changing then.

[Chris81]

Hi Chris,

When cat overtemp protection kicks in, the logged commanded AFR does not include the fuel component from COTP.

If you open your log file and your tune file with scantool->tunetool (ST->TT) linking enabled, you can position the scantool cursor on the place where you see richness, and then in the tunetool you can see the operating cells highlighted in the various tables...

To do this, you have to log the same pids as listed on the axes of those tables, and you have to use the same units for those pids between ST and TT, and it makes it easier if you set the TT fueling units to EQ and log both AFR and EQUIVRATIO in the ST.

Post up some log files and your tune file.

I use the linking feature between the TT and ST often.. i'll go ahead and log EQ RATIO tomorrow on a drive and i'll make sure all my units match up and we'll see what happens.

I included my latest tune file that is in the car now, as well as the log for one of my passes from the track the other night. I didn't have the wideband on it then.. but commanded and actual are dialed in. Even with it going rich on that pass, the car still ran 114.39 in the 1/4 at over 4200 ft DA.. so I know its making good power (that MPH corrected is 120.69 for comparison).

[joecar]

Some comments:

Log these
DYNCYLAIR_DMA
DYNAIR
(those will take 2 channels each, so you will have to drop some other pids to keep the channel count no bigger than 24).

What happened at the beginning of your run (see cursor in attached pic of your log)...?

LOL... you have some serious wheelspin...

The HOS2x1 voltages 850-905mV indicate a little lean at WOT... 920-930mV would be good (but do use a wideband).

As you run up the rpm at wot, the VE table hits that hole in the upper region (see the white cell in the 2nd pic)... fix the hole (raise it up a little).

[Chris81]

LOL good question, I didn't really notice that.. i'm not sure.. It didn't feel like it was spinning bad that I can remember.. my 60' was a 1.77 on that pass.

The splits were:
60' 1.77
330' 5.17
660' 7.95
MPH 89.2
1/4 12.33
MPH 114.39

I did notice the random drop in timing and my TP% in 1st gear.. I don't remember letting out or anything and all my traction control/active handling was off. Weird..

What do I need to be looking for using those 2 PIDS?