Closed loop idle oscillation when warming up

[travisty75]

I received some excellent help from others regarding my last thread, and hoped I could request some help for an issue that has recently arisen. The truck is an e67, 4.8 liter with a 218/227 cam, everything else stock, tuned on 87 octane.

Check the attached log (tune is included for reference) at the 5:10 mark for the oscillation that sets in. I can't see anything that is triggering why it swings as wildly as it does, and I also can't see why it settles back out just as easily; perhaps an emissions test? The truck still has all of the emissions components attached.

The truck will do it while in gear, too. It doesn't oscillate, but it does dip pretty heavily. It doesn't do it once the truck is warmed up, and it doesn't seem to do it when it's colder (all in reference to the coolant temperature, not ambient), but I've check it against other logs and it appears at very nearly the same time.


rev31_Almost Stall is the short log in idle that shows massive oscillation starting at 5 minutes 10 seconds. rev32 shows a dip while in gear at a stop light at the 5 minute 5 second mark, but doesn't show any oscillation (not attached due to file size).

[kevin87turbot]

You just need to do some tuning to get the fuel trims dialed in. It's pulling around 25% fuel at idle. Once you get it within 3-5%, it will no longer oscillate at idle.

[travisty75]

Thanks for the reply, Kevin!

I saw these corrections in the logs but assumed that was just cold temperature enrichments so I shrugged it off. All of my logs showed my MAF EQ Error being within 1 percent, but after further investigation I wasn't logging the o2 voltage necessary for the EQ Error; whoops.

[travisty75]

rev34_stable AF.hpl

48 97x_SD_MAF Cal_34.hpt


Can I ask for advice regarding idle tuning for the MAF? Based on the log and the MAF EQ Error, it's asking for another 5% in the idle cells. I ran 4 logs before that, Multiplying By % - Half each time, and every time it asked for another 5% at idle.

If I go off my STFT, it's pulling close to 20% at idle. My wideband is consistently reading 1.03-1.1 lambda, and normally rests around 1.05. I know it's slower to react and less accurate than the narrowbands, so not sure which I should trust here (the MAF EQ Error and Wideband, or the narrowbands/STFT).

The MAF curve looks great, the truck runs very well and transitions from idle to acceleration with no hiccups, and the results for the MAF EQ Error Histogram above idle are all very repeatable.


Is now the right time to switch over to following the Gen 4 Idle Tuning Guide?

[kevin87turbot]

rev34_stable AF.hpl

48 97x_SD_MAF Cal_34.hpt


Can I ask for advice regarding idle tuning for the MAF? Based on the log and the MAF EQ Error, it's asking for another 5% in the idle cells. I ran 4 logs before that, Multiplying By % - Half each time, and every time it asked for another 5% at idle.

If I go off my STFT, it's pulling close to 20% at idle. My wideband is consistently reading 1.03-1.1 lambda, and normally rests around 1.05. I know it's slower to react and less accurate than the narrowbands, so not sure which I should trust here (the MAF EQ Error and Wideband, or the narrowbands/STFT).

The MAF curve looks great, the truck runs very well and transitions from idle to acceleration with no hiccups, and the results for the MAF EQ Error Histogram above idle are all very repeatable.


Is now the right time to switch over to following the Gen 4 Idle Tuning Guide?

If you're going to use the wideband, then you'll have to force the vehicle into open loop first. Otherwise, the wideband will always read around Lambda 1.0.

I typically just use the narrow bands to dial in the idle and part throttle fuel trims. In your case, you'll need to remove at least 15% more fuel at idle.

[travisty75]

If you're going to use the wideband, then you'll have to force the vehicle into open loop first. Otherwise, the wideband will always read around Lambda 1.0.

I typically just use the narrow bands to dial in the idle and part throttle fuel trims. In your case, you'll need to remove at least 15% more fuel at idle.

Thanks for the advice Kevin.

Do you normally see a discrepancy like I have, where the MAF Error is showing wanting more fuel, but the STFT is pulling nearly 20%?

For the interim, I have my histogram ignoring any data points below 3,150 which is my high idle range. I'm going off the STFT while it's at an idle RPM to drop the MAF by that percentage, which is working just as it should. I just find it odd that my MAF Error is reporting something other than what the fuel trims are reflecting.

[kevin87turbot]

Thanks for the advice Kevin.

Do you normally see a discrepancy like I have, where the MAF Error is showing wanting more fuel, but the STFT is pulling nearly 20%?

For the interim, I have my histogram ignoring any data points below 3,150 which is my high idle range. I'm going off the STFT while it's at an idle RPM to drop the MAF by that percentage, which is working just as it should. I just find it odd that my MAF Error is reporting something other than what the fuel trims are reflecting.

If you were to force it to OL, then the MAF error would be correct.

[travisty75]

If you were to force it to OL, then the MAF error would be correct.

Ah, cheers! That makes sense. Sorry that I was not understanding that detail before.