E38 L96 Poor Idle Regulation / Stalling

I swapped an E38 L96 6.0 into my 2011 Silverado 1500 (also E38) and copied over the applicable parameters from a stock 2500 / E38 L96 tune. On cold starts in warm weather the idle RPM overshoots greatly, then if the ECT is under around 40C the RPM will oscillate once I take it out of Park (issue is reproducible in R, N, or D). Sometimes the oscillation is enough to stall the engine. The attached log shows the stall around one minute after starting. Current tune is also attached. Typically the longer I let the truck idle, the less severe the oscillation / likelihood of stalling.

All the values in the current tune are either from the original LC9 tune or the stock L96 tune where applicable. Where do I start?

Stock exhaust? O2's don't appear to be switching that well.
Injectors in the tune correct for that particular engine/yr model?
Intake stock from the original donor truck or from your original truck? Fueling is pretty decently off, but theoretically a stock engine should run fine
Checked for vacuum leaks or anything like that? Is intake manifold tightened down from center out correctly and double checked?

Quote:

---

Originally Posted by GHuggins

Stock exhaust? O2's don't appear to be switching that well.
Injectors in the tune correct for that particular engine/yr model?
Intake stock from the original donor truck or from your original truck? Fueling is pretty decently off, but theoretically a stock engine should run fine
Checked for vacuum leaks or anything like that? Is intake manifold tightened down from center out correctly and double checked?

---

Stock 1500 exhaust.

Stock L96 injectors. Tune values for injectors are from the stock L96 tune, right or wrong.

Stock L96 intake from the donor truck.

I have checked for vacuum leaks a few times just using carb cleaner to detect RPM changes, nothing more scientific than that. Intake was torqued following the factory sequence. I'll check the torques again.

Upon review I noticed the alcohol composition was reported as 47%. Since I only run gasoline I disabled flex fuel and reflashed. After idling for a few minutes the LTFTs swung positive. Does this make sense? New tune and log attached.

O2's are looking better - a little slow to start switching like possibly some age on them. Alcohol composition due to off fueling makes a lot of sense. It'll cause timing, idle and everything to change. Dial in your MAF and VE - should get things back more in line.

Virtual flex functions sorta like a extra-long-term trim, like a 3rd stage. Any error that causes LTFT to be off will eventually transfer over into alcohol %, resetting LTFT back to zero. It sucks, turn it off or install a real sensor.

Resurrecting this after a long time. Two logs are attached - one from January 27th where I was able to get it to stall when shifting from park to drive, and one from March 26th that shows the startup RPM flare which gets a lot more dramatic over around 50 degrees ambient. Same tune for both instances.

I put a 6l out of a Tahoe into this one. Give it a try and see how it starts. It's setup for electric fan, so if you have mechanical, you'll need to change that. Also put your MAF curve in and gauge setup. Something in the background of your OS isn't playing nice, so thought could try this to see if it plays better.

Cool, I'll give it a try. I still have the stock electric fans. What fields are you referring to for the MAF curve and gauge setup?

Quote:

---

Originally Posted by GHuggins

I put a 6l out of a Tahoe into this one. Give it a try and see how it starts. It's setup for electric fan, so if you have mechanical, you'll need to change that. Also put your MAF curve in and gauge setup. Something in the background of your OS isn't playing nice, so thought could try this to see if it plays better.

---

I tried this tune (6.0 Swap Truck.hpt) and the RPM surge still occurred on cold startup. Drivability was not good either, downshifts were rough and it wanted to roll a lot faster with my foot off the brake in 1st. Two log files attached, "1GCR7182 2023.05.12" is with the tune you provided, "1GCR7182 2023.05.12-2" is with the tune I had been using.


Attachment 131666
Attachment 131667
Attachment 131668
Attachment 131669

AND you're sure you don't have a vacuum leak on the intake tube anywhere? Rolled boot, missing breather hose or anything like that. Like I said you need to tune in your MAF curve or fueling for your new MAF location - it was really lean in that log - 18 to 20 % in places... Everything kind of points to a vacuum leak especially with the new complete OS being in it. It is possible the intake tube is just throwing it off, but sounds like vacuum leak from what you're describing.

Quote:

---

Originally Posted by GHuggins

AND you're sure you don't have a vacuum leak on the intake tube anywhere? Rolled boot, missing breather hose or anything like that. Like I said you need to tune in your MAF curve or fueling for your new MAF location - it was really lean in that log - 18 to 20 % in places... Everything kind of points to a vacuum leak especially with the new complete OS being in it. It is possible the intake tube is just throwing it off, but sounds like vacuum leak from what you're describing.

---

I put a smoke machine on the intake already and didn't see any leaks, and I sprayed around with carb cleaner and got no RPM response. I'll try smoking it again.

Make sure you start right at the air filter with the smoke tester. If there's not one then you're going to need to rework your fueling (dial in your MAF and VE tables) then go from there. Keep in mind if you're running breathers on the valve covers or don't have then plumbed right then that's a problem too. Earlier engines had pcv's and newer have the fixed orifices in the covers.

I smoked it again just downstream of the MAF sensor and didn't see a hint of smoke anywhere. I also ran it off the brake booster hose and got nothing.

While I was in there I checked the MAF and while it could be cleaner it didn't seem excessively dirty.

I would start by dialing in your fueling then. A lot of the problems may sort themselves out. You need to make sure your injector tables are setup for whatever fuel system you're running too.

OK I have been chipping away at this and made some progress. The cold start flare is less pronounced and the overall drivability is better, but I am still getting really high LTFT's in normal driving. I have the tune set to force it to speed density, logging LTFT, pasting the trim values into the virtual VE table and multiplying by percent half, reflashing, and logging again. Tune and log attached.

One thing I came across was that the original LC9 5.3 and the new L96 6.0 use the same downstream but different upstream O2 sensors. How much of a problem is this?

Attachment 134522Attachment 134523

That fueling is super lean. Make sure you're waiting 20 minutes of engine idle time or drive time after flashing before logging. All of the calculated temperature values have to relearn back to normal otherwise all of the data will be skewed.

Working on the MAF side of this. I've made a few iterations of logging LTFT once warmed up and applying those changes back to the MAF curve. On the last iteration the engine started running rough right after starting and quickly went into limp mode before I shut it down. Am I going in the wrong direction? Tune and last two logs attached (-3 log has more data, -4 was with the rev10 tune that put it into limp mode).

Sorry late to the party LOL

Your current rev10- file, the idle airflow and rpm tables are drastically different than stock. I compared against 2 different 2011 5.3 OE files.

These PCMs start doing funky stuff when you get too far away from OE settings when it comes to idle, throttle body control, etc. I know you swapped engines but based on the complaints you've had going back to the beginning of the thread, with idle issues, etc., my recommendation would be to put all those settings back to stock and start with the basic changes like increasing base running airflow if needed.

Going back to stock on those settings should cure most of the overshoot, etc.

Actually, I'd start over with your stock tune and change only the engine size and the injector data for the different injectors. Start from there and see what ya got. I bet it will immediately run better.

Thanks for looking into it, I will give that approach a shot. I've been taking more stabs at this lately and reading into logging MAF and VVE data simultaneously.

Quote:

---

Originally Posted by edcmat-l1

Sorry late to the party LOL

Your current rev10- file, the idle airflow and rpm tables are drastically different than stock. I compared against 2 different 2011 5.3 OE files.

These PCMs start doing funky stuff when you get too far away from OE settings when it comes to idle, throttle body control, etc. I know you swapped engines but based on the complaints you've had going back to the beginning of the thread, with idle issues, etc., my recommendation would be to put all those settings back to stock and start with the basic changes like increasing base running airflow if needed.

Going back to stock on those settings should cure most of the overshoot, etc.

Actually, I'd start over with your stock tune and change only the engine size and the injector data for the different injectors. Start from there and see what ya got. I bet it will immediately run better.

---

I agree with this.. Too many times on this forum you see "copy all the stuff out of the X file" That is terrible advice. Get the basics fixed like displacement and start tuning like that engine never came in the vehicle.

There are too many modifiers and what not that we cannot see.

OK, so I went all the way back to the as-found tune from the 5.3, changed the displacement, and copied over all the injector parameters from the 6.0 tune. No startup flare but the RPM started oscillating strongly within a few seconds. Log and tune attached.

Need to let it run longer. It looks pretty lean and the trims never activated. I'd run it another minute or two and see what happens when the trims come online.

Use this channel config. You have way too many channels going.

Take 2, waited longer for the oscillations to die out, then went for a short drive around the neighborhood.

Quote:

---

Originally Posted by edcmat-l1

Use this channel config. You have way too many channels going.

---

Did you get a chance to look at the most recent log?

Narrowbands say it's dead lean the entire time and it never goes into closed loop. I'd recommend you force closed loop using your scanner controls and dial in the VVE and MAF using your short term trims.

Quote:

---

Originally Posted by edcmat-l1

Narrowbands say it's dead lean the entire time and it never goes into closed loop. I'd recommend you force closed loop using your scanner controls and dial in the VVE and MAF using your short term trims.

---

Since I am a dummy, I didn't re-disable DoD and Flex Fuel on the last run, which is why it ran so poorly. With that fixed, the drivability issues I'd been having are gone. No startup flare, no wandering idle or stalling, much better drivability overall. Still very lean overall but a huge improvement for daily driving. Thanks for the help.

Was there ever a solution found to this surging idle issue?

Start your own thread.