TCC coming out of lockup, cammed LQ4 swap 2005 Tahoe

[redhat]

Pretty new to tuning here. I had an e-mail tune for my 2005 Tahoe. Truck runs good, has good power, but fighting an issue where with cruise on at 65mph, going down a grade, I can feel the TC locking and unlocking. I can see some misfires during coast, and I do have misfires when idling, but I have been told this is to be expected even with a baby cam. While driving I do not have any misfires.

I did already try making the MIN TCC PWM delay to 90. That did not change anything.

Truck is a 2005 Tahoe Z71 with an LQ4 swapped. LQ4 has a baby Summit 8718R1 cam, LS6 valve springs, Summit stock replacement pushrods, Melling trunnion upgraded stock style rocker arms. Have a low mileage set of OE LS2 injectors in it that were flow benched and all tested good. Running stock 5.3 manifolds, stock cats and Y-pipe to a 3" MBRP Cat-back. Running the stock LM7 intake manifold with OE airbox and intake tube. A lot of stock stuff. Only thing that I am unsure of, age wise, is the O2 sensors. Truck has 304k and these could be the original.

I have all new coils, NGK TR6 plugs gapped at .35 and new plug wires.

I have uploaded the tune and most recent datalog and the VCM scanner config. Around the 15 min 20 sec mark I begin a descent down a grade on the thruway maintaining 65mph with the cruise on. This is when I mostly will notice this lock unlock lock unlock situation.

Appreciate any thoughts or advice.

[kingtal0n]

Interesting, looks like some kind of coast mode or coast down table is being activated on and off repeatedly. Looks like these
https://forum.hptuners.com/showthrea...s-causing-this

https://forum.hptuners.com/showthrea...l=1#post305272

The Coastdown table is under "Idle Spark Advance".

Maybe this

you need to make the top left corner of the main spark tables the same as the base idle spark and the coastdown spark tables. 40+ deg is way too much timing and will cause the cam surge, copy that area of the base idle table to the main spark tables and smooth the transitions around 1200-1800 rpm. It must be a smooth transition between the 3 tables when you are on and of the gas at light loads/low rpm.

https://forum.hptuners.com/showthrea...l=1#post297083

I don't tune DBW so I'm not sure why the coast down table isn't in your file or does not appear to be under idle spark advance. however it may simply be referencing the idle spark in drive table, the timing at 1700rpm appears to be 17.5* which is similar.

1. It may be a coast table is missing from your file and needs to be added
2. It may be that the timing in idle spark in drive should be increased to match the cruise "coast" timing
3. You may have too much coast airflow from throttle cracker and throttle follower tables (or other places) causing the engine to hang and cruise instead of coast or engine brake

For sure, the timing should not be jumping like that. I would also prefer the TPS to goto 0% when I lift from the gas pedal but that is just me, maybe not your preference.

[redhat]

Thank you for that, I am going to read through that and look through my tune.

[Hondaeater]

Thank you for that, I am going to read through that and look through my tune.

Links are for Gen4, read if desired.

redhat,
1st... Max out ALL the misfire tables. Did that solve the issue? Misfires cause havoc on automatic transmissions.

If NOT solved, use special functions green button in Scanner to turn off TCC lock up. Drive that same route as before and at the same 66-68 MPH off the pedal, and check behavior, try toggling the TCC using the special functions. Log this with current channels list, then save the list and if desired load this channels list below and make another drive log. It does not need to be the same area or MPH. Just drive with some stops and steady states, normal.
Add your Wide Band if you have one, add it between the AFR Commanded and the Equivalence ratio commanded please. Stay Organized.

Also set high rpm disable HIGHER than steady state Hi/Lo rpm threshold.

Here is a channels list that may help reveal problem areas, and your log with the misfires helped too. You can only log about 25-30 MAX channels at a time in GM Gen3 for good data. (20-25 for best results).

Stay tuned,
Hondaeater.

[jsf55]

Brake pedal switch adjusted correctly and spring on it too stop it vibrating and triggering the switch ?

[Hondaeater]

Hey that's a really good scenario it could cause a lot of issues but I don't believe in this case that would be the issue. If it was a brake pedal switch I think it would happen more consistently in the log. This happens with misfires, zero throttle, at speed.

[kingtal0n]

Notice the TCC is going into "coast mode" and the throttle position is cycling all by itself to maintain a 1700rpm cruise, and look at the spark timing it constantly jumps from 39* to 17* In peaks and valleys. There is some mode which involves the throttle and timing constantly switching between tables causing this. It may be a missing table or something to do with the airflow 'mode' to set or raise some values to keep it from swapping tables.

[redhat]

Links are for Gen4, read if desired.

redhat,
1st... Max out ALL the misfire tables. Did that solve the issue? Misfires cause havoc on automatic transmissions.

If NOT solved, use special functions green button in Scanner to turn off TCC lock up. Drive that same route as before and at the same 66-68 MPH off the pedal, and check behavior, try toggling the TCC using the special functions. Log this with current channels list, then save the list and if desired load this channels list below and make another drive log. It does not need to be the same area or MPH. Just drive with some stops and steady states, normal.
Add your Wide Band if you have one, add it between the AFR Commanded and the Equivalence ratio commanded please. Stay Organized.

Also set high rpm disable HIGHER than steady state Hi/Lo rpm threshold.

Here is a channels list that may help reveal problem areas, and your log with the misfires helped too. You can only log about 25-30 MAX channels at a time in GM Gen3 for good data. (20-25 for best results).

Stay tuned,
Hondaeater.

Thank you for this, I am finally getting back to this and will log those channels in the next day or so and report back.

I've been fortunate to have some free time as of late so I am trying to dive deeper into troubleshooting this, I've done a few things. Additionally, I had been borrowing a MVPI 2 from a friend. Couple weeks ago I bought my own MVPI 3, re-licensed my P59 and now have a lot more flexibility to do what I need.

Here's what I've found out/done.

First off, way back when, probably March/April, I did bring this TCC coast/locked oddity up with my tuner and he didn't have much to offer beyond saying everything is standard GM calibration, no idea what's going on, etc. -- he did suggest setting the TC lockup speeds higher. No fault of his, I didn't think anything of his was at fault. So he did send a file with higher TC lockup speeds, 49MPH or so. After driving since March/April to present, I drove on it enough to know that didn't make a lick of difference. Additionally, I wasn't a huge fan of it locking up at that speed. It seemed like I was always coming in and out of lockup as my normal driving routes -- that is a very common threshold speed. So I ended up changing those lockup speeds to factory default calibration.

Second, I went under the TC Min Release table and set the High and Low TPS High-Speed threshold to 0 percent. I took a drive with that set, and noticed that it then kept the TC locked, it didn't go into coast mode. It seemed a whole lot better. I am not sure if it was kept calibrated like this would be detrimental to its longevity or harm it. I am assuming GM has these trucks "freewheel" to save MPGs? From my reading, I guess some cars, such as an LS2 GTO are factory calibrated to keep the TC locked and this section is disabled as such.

My last as most recent step I did, I put the TPS settings back to stock and maxed out my misfire tables for Idle (not moving), Idle (moving) and medium speed up to 1400RPM. I went for another drive and still experienced the coast/locked "pulse" as I'll call it. Now that I am typing this, perhaps I should max out a few more rows of the medium speed table maybe up to 2000RPM or so. (Now I'm seeing Hondaeater mentioned maxing all out -- gotta do something with that).

Within a day or so I'll post up another data log with the channels suggested by Hondaeater and I'll also post up my latest calibration.

Thank you all for you help, sorry its been so long, appreciate y'alls time.

[Alvin]

There is a TCC brake fuse on a lot of platforms that if it should happen to go bad it will release the TCC any time you are not significantly on the gas.

Also, looks like you already found it but trucks are generally programmed to coast with the TCC off. You can copy settings out of a auto car like a vette, F-body, or GTO and change that.

If it has a cam. I wouldn't mess around with changing some misfire tables and not others. Just disable misfires

[redhat]

There is a TCC brake fuse on a lot of platforms that if it should happen to go bad it will release the TCC any time you are not significantly on the gas.

Also, looks like you already found it but trucks are generally programmed to coast with the TCC off. You can copy settings out of a auto car like a vette, F-body, or GTO and change that.

If it has a cam. I wouldn't mess around with changing some misfire tables and not others. Just disable misfires

Thank you. I?ll look for a TCC brake fuse and check it out. Also, I will disable all misfires in all tables.

Am I correct in thinking that even if I have a baby cam, it?ll show misfires as the PCM is looking for that smooth waveform from what would be the cam/crank readings of the stock cam?

Appreciate it. Learning a lot here.

[redhat]

Alright, so I did some looking and maxed out all of my misfire tables under Revolution and Cylinder modes. Previously, I had only maybe up to 1400RPM maxed out. I went out for a drive and WOW, NO Lock/Unlock (Coast/Locked) switching. Big thanks to Hondaeater and Alvin for the advice. And everyone else on here for your info. I owe you all a beer.

Super pleased -- I went on a long drive where I'd usually hit all of my trouble spots and it acted excellent.

I did perform a datalog with the DBW channels (and a few more for TCC) suggested. I will attach that here along with my current calibration. If anyone would take a peek and if there are any suggestions or tweaks, I'm all ears.

Also hoping with keeping this TC locked more, I'll squeek out a little better than 12.5-13MPG.

Thanks again y'all.

[redhat]

Did another log, seems to be behaving a lot better. I think I may still feel some of the locking and unlocking, but then I look in the log where I believe it was and it looks like its acting normal.

I did go back to stock PWM TCC delay... perhaps I am feeling some TCC bobble. Think I may adjust that back to min 90 and see how it is.

Here is the log: Don't mind the P0455 showing. Guess I don't know how to tighten a gas cap.

[redhat]

bump

I upped the speed that of which the TC locks up at. In doing that, I VERY clearly saw the condition I am experiencing. It is not TCC. Seems to be spark/airflow related.

I saw the tach bounce between 1100 to 1350/1400 rpm while coasting down a small grade.

[redhat]

Think I finally figured it out. Idle spark advance in-gear.

PCM was commanding coast when descending down a grade. Since TPS is low during a coast situation, the PCM then referenced the idle spark advance in-gear table which for about 0.20 airmass was calling for 16 degrees of timing. Where as in my high or low octane tables, this would be calling for 22+ degrees of timing. So in a situation where it either is (A) calling for coast, or (B) coasting, then locking up, then coasting, it would be switching between 16 degrees through 22+ causing a surge. Which of course then if it was surging it would then go back to locked and it would repeat.

Ended up coping the high octane table and placig it for idle spark advance. Drives superb now.