Can't figure out stalling problem

[Jason B]

I have basically an LS2 with a Summit 8706 cam, TBSS intake, 90mm cable TB. Running off a 411 pcm that was originally for a 5.3. I tuned VE, MAF, timing, and got it running and it runs great.

The problem is when I rev it to 1500 rpm or so and let off it usually dies. Like the key is turned off, doesn't even try to recover.

The weird part is, if I do this in gear, since it has a fairly loose converter, it doesn't even do anything weird. RPM drops right back to idle no problem.

Also with the a/c on, if it doesn't stall it'll turn the a/c clutch off (to prevent stalling) but it usually stalls anyway.

I've tried a lot and nothing really helps. Last night I changed the IAC and adjusted the TB blade closed a little so the IAC would maybe help when it tries to stall. Now when I do the same thing the rpm will go way down and it won't stall every time, but it didn't change much, it'll still stall. I really don't understand why it never stalls when I do this in gear.

Any ideas?

The scan file is huge, I left it on while changing the IAC but near the end is a rev to 2.4% throttle and a stall like it always does.

Attachment 106060
Attachment 106061

[QTR FMS]

Hi,

try this tune i have made some changes to the timing, it should help a little bit but i dont think it would solve the issue, post your stock tune i want to check what changes you made to the idle airflow.

[Jason B]

Hi,

try this tune i have made some changes to the timing, it should help a little bit but i dont think it would solve the issue, post your stock tune i want to check what changes you made to the idle airflow.

I'll give it a try tomorrow after work. I noticed you changed a few ETC things. It's a cable TB. Not sure what that does.

The stock tune file is probably be overwhelming, like I said it use to be a 5.3 tune file. I tuned it for a mild 5.3, a huge cammed 5.3, then a mild cammed 5.3, now it's a 6.0 tune evolved from all of that.

One main concern I had is what to change when going from a 5.3 to a 6.0. A search lead me to believe that most everyone only changed displacement and tunes from there. But in a stock 2002 6.0 there are a lot of airflow differences.

This is the original tune file that I started with Attachment 106066


This is a stock 2002 cable TB LQ4 if you're curious for referenceAttachment 106067

Thanks

[QTR FMS]

I'll give it a try tomorrow after work. I noticed you changed a few ETC things. It's a cable TB. Not sure what that does.

The stock tune file is probably be overwhelming, like I said it use to be a 5.3 tune file. I tuned it for a mild 5.3, a huge cammed 5.3, then a mild cammed 5.3, now it's a 6.0 tune evolved from all of that.

One main concern I had is what to change when going from a 5.3 to a 6.0. A search lead me to believe that most everyone only changed displacement and tunes from there. But in a stock 2002 6.0 there are a lot of airflow differences.

This is the original tune file that I started with Attachment 106066


This is a stock 2002 cable TB LQ4 if you're curious for referenceAttachment 106067

Thanks

IN USE 12 24 20.hpt

the main difference between 5.3 and 6.0 is the airflow and torque from the extra displacement, and then the injectors which you tuned for, there are other small tables but we usually change them anyway or they dont really make any difference.

try this tune and post datalog, we will make small changes to base idle airflow and then we can tune the throttle follower if necessary,

i see that you made some changes to the ac torque and accessories torque, i never had to mess with them, if you didnt find any improvement with them you might want to change it back to stock.

[Jason B]

Well, that made it worse. I idled it cold to almost operating temp to log RAF. Took it for a drive, might seem to pull a little harder down low. I noticed my fuel trims are positive and sticking positive with PE. Not sure if thats because I tuned them in hot humid weather and now it's 68 degrees and dry.

Anyway it stalls worse, hunts worse. I put my tune back in and it still tries to stay running when I rev to 1500 and let it off, it didn't stall but rpm dipped low.

Attachment 106081

Attachment 106082

[kingtal0n]

I cant look at the file but you describe one of two possible situations

either DFCO or the area the fuel map runs when the engine is "coming back to idle" isn't giving it enough fuel (does the wideband go lean or "-.-" when the engine is shutting down and stalling?)

OR

You prob need to play with the Idle airflow, specifically the PID controller portion, that is the amount of air and time duration for that airflow when the throttle is pressed depending on the RPM the engine is at. Do you by any chance understand how PID works?

[ryan_axberg]

I would set the spark table in gear and park and also main spark tables in the idle areas at 20 degrees. that give you good room to add spark to raise rpm or remove spark to lower it. I would also make the underspeed spark modifier table add 18ish degrees by -250 rpm and interpolate to zero. I don't really like using ltit either, if you get everyting dialed in I just like using stit. I would also log throttle follower and throttle cracker, and start up airflow. have you dialed in your braf in park and in gear using your stit?

[QTR FMS]

IN USE 12 28 20.hpt

it will get worse before it gets better, right now im removing some idle air flow to get the stit and ltit close to zero, as right now you are fighting the pid and its causing you to stall, once we are done with base running airflow, we then can add more idle follower to make it react better to decel.

[Jason B]

IN USE 12 28 20.hpt

it will get worse before it gets better, right now im removing some idle air flow to get the stit and ltit close to zero, as right now you are fighting the pid and its causing you to stall, once we are done with base running airflow, we then can add more idle follower to make it react better to decel.

Ok I'll try that tomorrow. Would it help to reset the LTIT's?

[QTR FMS]

Ok I'll try that tomorrow. Would it help to reset the LTIT's?

STIT usually learn quick so it doesnt matter much, but to be safe disconnect the battery before you try it.

[Jason B]

It's only getting worse.

I tried it with the LTIT's reset also.

Attachment 106104

Seems like I've done all this before. It runs fine. Just if for some odd reason I want to rev it to 1500 and let off in park it stalls. Most people probably wouldn't notice this or care.

Seems messing with IAC stuff helps. Maybe I'll continue in that direction.

[QTR FMS]

It's only getting worse.

I tried it with the LTIT's reset also.

Attachment 106104

Seems like I've done all this before. It runs fine. Just if for some odd reason I want to rev it to 1500 and let off in park it stalls. Most people probably wouldn't notice this or care.

Seems messing with IAC stuff helps. Maybe I'll continue in that direction.

IN USE 12 29 20.hpt

the reason its getting worse is that im removing timing and airflow, i removed some timing to see if vacuum would drop, 26 degree at idle is too much and you are not giving the underspeed enough torque to control the idle,

and the idle rpm is too low for your cam it would probably be happier at 850rpm, for now i did set it to 800 and 26 degree.

i have added back some base air flow and increased the throttle cracker and follower.

[Jason B]

Any idea why it doesn't have any problems in drive?

Again, I rev it to 1500 rpm in park and let off it dies like the key is turned off.

I rev it to 1500 the same way in gear and let of and it doesn't even stumble, surge, dip, nothing. Goes right back to set idle. Wouldn't that require more torque?

I've tried 800 rpm idle. I really don't think it needs an 800 rpm idle. I had a bigger cam in a 5.3 that idled at 800 no problem. Same truck, this is a modified tune from that engine.
Heres one of them, not sure if it was the final tune or not.

Attachment 106107

I think right now I'm going to update my VE and MAF tunes and run those to see if anything is off, then I'll get back to this.