4.8 e67 with cam, drives great, but has an odd idle characteristic

[travisty75]

4.8, e67, Summit 8720r1, valve springs, all stock otherwise.

The truck drives great with the exception that it will, at idle, move into Open Loop and command 1.14 Lambda, stays at that for 8 seconds, then switches to .85 lambda. It will hold that 5 seconds, then revert back to 1.0, my target idle.

I didn't notice the initial 1.14 command, but I did notice when it switches to .85 because the truck will start to hunt a bit. No check engine lights throughout the entire 45 minute log, no drivability issues.. just this weird thing.


Could it be something like a purge event for the EVAP? Cat test? When I saw the .85 I assumed that was my Catalysts Over Temperature kicking in because that would make sense.. I guess? It's been really hot here, so I'm just trying to connect whatever dots I can. Snippet of the log and the tune are attached.

EOIT Adj_43_weird idle dips.hpl
48 97x_Big Changes_Lowered AC Air.hpt

[5FDP]

Turn the cat test off in the exhaust part of the engine diag tab.

You left both the post o2 sensor test and cat test on. Those swings in commanded AFR is it doing a test.

If you can't see those tables you likely have a newer version of the VCM suite that removed those tables because of the emission stuff with the EPA. Other people here could remove them for you still, just not me.

[travisty75]

Turn the cat test off in the exhaust part of the engine diag tab.

You left both the post o2 sensor test and cat test on. Those swings in commanded AFR is it doing a test.

If you can't see those tables you likely have a newer version of the VCM suite that removed those tables because of the emission stuff with the EPA. Other people here could remove them for you still, just not me.

Thanks 5FDP. I assumed it was something running in the background and had heard of those tests, but never knew how to log those things.

I don't have access to those tables/options. Short of someone stumbling across this post who has that capability, I don't know how/who to ask for that.. All the same, so long as I know why those things are happening, it doesn't bother me too much.

[5FDP]

If I owned a MPVI2 I would change them for you but I still have the original MPVI with older software that lets me see everything still.

[blindsquirrel]

48 97x_Big Changes_Lowered AC Air-INVISIBLE_SETTINGS_CHANGED.hpt

[travisty75]

invisible tune

Thank you BS!

[travisty75]

Just wanted to again say thanks to both of you. I flashed that version in with no other changes, and logged the drive to and from work. Everything is cleared up and the truck does (and doesn't do) exactly what it should be.

[5FDP]

Good to hear.