Rich trims at idle but cruise is fine 1997 corvette

[mvvette97]

I can't seem to figure this out. The trims during a drive are pretty good in the -2 range but at idle they drop to -6 to -8. The car has stock cam with just headers and blackwing filter. I dropped the VE in the idle range but it didn't seem to do anything. Why didn't the VE change the fueling any? Any idea what I can change to get the idle leaned up some? Everything else looks to be good.

[WeathermanShawn]

Contrary to a lot of information out there, at normal ECT Idle fueling is still primarily controlled by the MAF (if MAF Enabled). If you don't believe me log your MAF frequency at warm Idle..then add or subtract 10%..and watch your fueling change by +/- 10%. You will see the influence of the VE Table more on cold Idle and Start-Up.

Idle LTFT's are also controlled by B3807 and B3808. In other words it is a totally different fuel cell that controls Idle. The bottom line is what you are describing is relatively normal. If it really concerns you manipulate your Idle MAF frequency, but be prepared that if you hit that same MAF frequency at some other point in driving, your fueling/LTFT will also be affected.

[mvvette97]

thanks Shawn, it looks to me then it would never enter into the B3807 since the TPS is at 5% at idle since there is no IAC, Since the value is set at 1.19, is this correct?

[WeathermanShawn]

thanks Shawn, it looks to me then it would never enter into the B3807 since the TPS is at 5% at idle since there is no IAC, Since the value is set at 1.19, is this correct?

I think what this is reflecting is the following. Idle LTFT's are controlled separately from 'Non-Idle' LTFT's. If you log GM. FTC you can see this. So what you are describing is perfectly normal. If you are wanting to lean out the Idle, my suggestion is do it first through the MAF. I.E., log MAF Frequency just at Idle. If you are at -6 to -8 LTFT's just at Idle, adjust just the very lowest MAF Frequencies (found at Idle).

Does that answer your question?

[mvvette97]

yea that makes total sense. I had thought about that but so many people say don't mess with the maf but I'll try it anyway. Pretty easy to change back if it doesn't work out.

[WeathermanShawn]

yea that makes total sense. I had thought about that but so many people say don't mess with the maf but I'll try it anyway. Pretty easy to change back if it doesn't work out.

It will work. Guaranteed!

Just apply the same correction for all the lower MAF Frequencies also (all the way down to 1500 Hz). Though you may not him them in winter, you may hit those lower MAF frequencies in warmer weather. The only potential downside is you may hit that same MAF frequency during decel at 0% TPS. I normally utilize DFCO, so it is no worry..but just in case you see an errant LTFT during decel..you will know why.

Good luck..

[joecar]

+1

MAF table is just as editable as VE table.

[mowton]

I recommended (and provided instructions) you tune in the VE and MAF in your Corvette Forum thread you started......provided MAP, Dashboard and WB info via e-mail. How did that go? After that, logging the RAF would bring the LTIT/STIT into tune.

Ed M

[N0DIH]

Not sure how the 97 Vette file looks, my 2000 Park Ave Ultra has specific O2 switch points for cold, idle, decel, normal, accel and high flow conditions. Have the O2 switch points been messed with?

http://i159.photobucket.com/albums/t142/mompower/Tom/PCMTuning/O2_switchpoints.png

[voda1]

After that, logging the RAF would bring the LTIT/STIT into tune.

Ed M

Can't log RAF in 97 as the required pids are not supported. You can log SAE.MAF at idle and use that. Make sure your saving LTFT data by checking if: File -- Edit -- Properties-- Logging tab , AutoSave metaData - LTFT cell is checked. You can than see LTFT data by key combination Shift-Control-F2.

Could you post up your tune and log?