LS3 Swap into an LS2 GTO

[Cdeg2969]

Good morning all... Just did a LS3 (376/480) with GM hot cam swap into an LS2 GTO with a blown motor for a customer. I have attached the base tune from the LS2 and the latest one I doctored to get it to run with the new engine. I am having a couple of issues getting the tune dialed in... (this is the first time I have done a LS2/LS3 tune conversion.

Car has a soup to nuts engine swap... LS3 MAF, LS3 to LS2 MAP Converter and a Lingenfelter Crank trigger converter box (58x-24x) . Car is a 6 speed manual.

Main Issues...

Car starts and runs.. originally I had a hot start issue but I think when I raised the startup idle air it has smoothed out (for now...)

Car start and runs.... BUT

#1- When parked... in neutral, the car revs up fine... as it revs down it hangs at 1300-1600... it SLOWLY (over the course of 10 seconds or so) drops to the commanded idle of 975. I tried to adjust the idle airflow (as many have told me a too high will cause hanging) but it did nothing, so I moderated them and left them alone. Car idles at 975 w/ 1.38 lbs/min MAF. Timing seems to stay around 18-20... ish...

#2- When the car is driving (drives fine, runs great up to redline) and I come to a slow stop at a stop light during coast down... The opposite happens... revs drop seemingly too fast and bounce about 500rpm (sometimes shutting off) then cycling back up towards the 975 range.

I am guessing that one of these issues has to do with airflow and the other with timing or adaptive idle... It seems like no matter what I do I cannot get either issue resolved. Maybe I am not messing with the right tables.


This is the first time for me trying to tune a newer motor in a car with an older operating system. The LS2 computer has some options that the new LS3 does not have and vice versa. Any help would be appreciated as I want it at least drive-able to get it to the dyno in the spring. Mechanically everything on the car is A+ and new.

I am at work now but will attach the tune later from the original LS2 computer and the tune I have been working with.. Thanks for your assistance guys!

[schpenxel]

Copy of tune/log?

[mowton]

I'll wait on the tune and log but you will have to update your IAT scalar (see an LS3 stock tune) and IIRC there might be a TB incompatibility (Gold vs Silver blade, opening direction etc.). Believe you need the silver LS2/E40 type.

Ed M

[Cdeg2969]

Here you go gents... This is what I have so far... Car is starting and running BUT....

Hangs idle @ 1400-2000 during rev down (car in place)

Idle drops off too quickly while coasting to a stop... drops to 500rpm.. and comes back to commanded 950ish...

I have attached the LS2 base tune... The LS3 tune that is in the car now... and then the log. During the log car is idling then I rev'd once to 2200 or so... then rev'd again. Car was warm when logged.

Thanks for ALL of your help.


CHRIS

[schpenxel]

I would take the min airflow values at 1200 RPM's and use those for the higher RPM's instead of continuing to increase them

I would also (at least for now) make all the gears/P/R/N, etc. the same instead of them being different for different gears.

You'll want to log idle adapt spark (may be called something slightly different but you should be able to find it) as well as anything regarding idle that you can find. Idle commanded, idle error, etc.. whatever you can find on idle.

Mess around with that and report back how it goes

[Eaglegoat]

I would take the min airflow values at 1200 RPM's and use those for the higher RPM's instead of continuing to increase them

I would also (at least for now) make all the gears/P/R/N, etc. the same instead of them being different for different gears.

You'll want to log idle adapt spark (may be called something slightly different but you should be able to find it) as well as anything regarding idle that you can find. Idle commanded, idle error, etc.. whatever you can find on idle.

Mess around with that and report back how it goes

I don't recommend making all the airflow minimums the same. I like to put the car in gear and get it rolling with no throttle input and log desired airflow at different RPMs using the scanner controls. I usually do this for 1st-4th gear. Make sure you turn off idle adapt timing when you do it.

[schpenxel]

I don't either permanently, but wanted to see what would happen with the issues he was having

[Cdeg2969]

I don't either permanently, but wanted to see what would happen with the issues he was having

I will try this... I will also turn off the adaptive idle and give her a run. It has to be somewhere else in another table that is making this occur because I even adjusted many of these numbers back to a stock LS3 and it still hung... I will try this suggestion and turn off the adaptive idle spark and see what she does...


CHRIS

[Cdeg2969]

SO it did a very similar thing... I adjusted idle air and it still hangs...

Here is the new log... with the additional perimeters..It appears car is pulling 4-6 degrees of timing at idle to reduce car rpm to desired RPM of 975.

Thoughts?

[schpenxel]

Try reducing that whole table by 25% or more. I'm trying to go too far just so we can see if that's what it is or not. It basically acts like an idle set screw on a carburetor.. won't let the throttle blade close any further so it pulls ignition timing to try to bring the RPM's down

The idle adapt being negative means it's getting too much air usually, or at least that's what I've always thought.. what I've seen on mine is if you can get it so idle adapt is just barely negative that seems to work out to the most stable idle without any hunting, etc.

Can't hurt to try bringing that table way down just to see what happens

Also possible there's a vacuum leak or some other oddity that goes along with that swap that I don't know about...

[Cdeg2969]

Try reducing that whole table by 25% or more. I'm trying to go too far just so we can see if that's what it is or not. It basically acts like an idle set screw on a carburetor.. won't let the throttle blade close any further so it pulls ignition timing to try to bring the RPM's down

The idle adapt being negative means it's getting too much air usually, or at least that's what I've always thought.. what I've seen on mine is if you can get it so idle adapt is just barely negative that seems to work out to the most stable idle without any hunting, etc.

Can't hurt to try bringing that table way down just to see what happens

Also possible there's a vacuum leak or some other oddity that goes along with that swap that I don't know about...

I tried (a few days ago) to bring the whole table to the stock LS3 levels... I have a stock LS3 tune out of a corvette to compare.... Did the same thing... I cannot get any further with tuning this thing if the idle wont rest...

CHRIS

[Lakegoat]

I would stick the LS2 MAF back in there and try that.

[Cdeg2969]

Even though I have the LS3 MAF and LS3 MAF frequencies into the LS2 tune?

Any other thoughts?

[Lakegoat]

Base running airflow looks high, Startup airflow looks low, ETC Scalar wasn't changed, I didn't look at the timing.

[Cdeg2969]

Base running airflow looks high, Startup airflow looks low, ETC Scalar wasn't changed, I didn't look at the timing.

I hear that switching out the LS3 throttlebody to the LS2 might be the only way to get this thing stable again...

[Lakegoat]

I heard that the LS3 maf was hard to tune in other setups. I didn't know if it was true, so I didn't mention it. Mine is SD tuned, so I don't have to worry about one.

[SultanHassanMasTuning]

I would tune it SD

[schpenxel]

I would go SD as well. I never got my LS3 style MAF to have a stable signal on my LS2, even with a honeycomb added

And you're probably right on the throttle body.. I've heard a lot of weird things about LS2 vs. 3 throttle bodies but haven't personally messed with them enough to be of any help.

[cavy.417]

I just put a 416 ls3 in my 06 gto last year. But I sd tuned it and have the ls2 throttle body which I think you should switch to the ls2 style. But I think you may be going at it a little wrong in my opinion. Instead of using the ls3 tune file to make this new tune. Just tune it as it was any other gto (what I did). Only thing I used from a ls3 tune was the spark timing. Sure it has more airflow and power but the computer can be tuned for it. I started from a cratch gto tune. I'll get on my computer and post my tune for you to look at.

[cavy.417]

This has LS9 injector data and no maf. LS3 416, LS2 ported throttle body, LS3 heads/intake.