This is not on my car but I figure the tuning basics should be tthe same...

The car is a 3.8L Camaro, with a custom T70 turbo kit I built.


It has all the supporting required fuel modifications. 60lb injectors being the mainone we changed from a previous tune that worked.


Previous setup was just ls1 injectors and an FMU which worked but not optimal we would say. So we swapped out to the 60 lb injectors and removed the FMU. We got a base tune done on a mustang dyno and when we cranked up the boost to 10 psi it hit a "rev limiter" at 5000 rpm. Its not really a rev limiter but its the best way I can describe it. It was a very harsh stumble. It does this also at 7 psi, but is ok at lower boost. This is really weird since the AFR is solid and fat at that. There is no knock and it has plenty of spark and correct gap on plugs.

IF we roll on the throttle slowly it wont hit that stumble but if we go WOT immidiately it will do it everytime at 5000 rpm. I can't seem to put my finger on why.

My only guess is that the MAF is getting maxxed out and and there is a hole in the tune? But at the same time AFR was solid 10.5.... fuel pressure never dropped...

Im trying to correlate similar experiences on an LS1 to be able to solve this issue. Anyone care to give me any tips?
TIA

 

Sounds to me like you are maxing out the MAP sensor. Time to go to a 3 bar setup

 

no need for 3 bar, should be able to tune via the MAF until it maxes out, then PE table should do it.

 

I know from reading the forums at hptuners that there is a "predictive" knock retard based on delta airflow, or the sudden increase in airflow. Not sure which tables exactly and especially on a V6, at 5000 RPM there must be a huge "delta airflow" when you mash the throttle, since AFR stays in-line this would be my first guess... let us know what you find.

 

humm, I'll deffinately look into that, sounds like something that could be it....

no other ideas?

 

Pretty much it has to be fuel mixture, spark strength, or ignition advance.

You ruled out fuel mixture.

Spark strength is probably not an issue, since the gap is good and it handles a gradual transition ok.

I'd log the total ignition advance, and see if something flaky is happening there.

The only other thing I can think of is a a/f problem that is so quick that it's hidden by the time it reaches the w/b sensor. But the stumble should be quick too in that case...

 

everything pushees me to believe its running lean suddenly even though on the wideband the AFR was solid up to that point. At lower boost it doesnt do it.

Can anyone show me and example of a PE table on an ls1 wher ethe MAF maxes out and the PE table takes up the slack afterwords? I am pretty sure the MAF is toast on this setup and when it goes to the PE table there just isn't enough fuel possibly? Still doesn't quite explain why it wont do it if we lean on the throttle slowly....

I guess what I need to compare with someone here, is how much of a jump in the PE table do we need to have once the MAF is maxxed out? Right now it has a 1.2 value on it at 4000 rpm and up, IVe tried putting it at 2. Should this be more in the order of 3-4 if the maf is maxxed out?

 

Tiago, have you posted on our forum?

The V6 fueling is quite different than that of the LS1.

Also might want to give the guys at INTENSE a call. They tune their turbo car using our product as well.

 

Does the injector pulsewidth change when this happens?

 

yes the injector pulsewidth gets cut back when this happens.... it seams to be reading about 11ms up to that point then jumps back to 6ms....O2 readings drop from 700s to 10 when this happens, and the injector pulsewidth as explained above.



Magnus,
this is posted on the hptuners board too, Linxs posted it, it is his car. I have the maf displayed in HZ on our scanner log, but it never actually displays it, so I can't confirm that its maxxed, only that it reads the maxximum value in the MAF table time and time again...

 

anyone? bueller?

 

Well I guess your pcm is doing it on purpose since pulsewidth cuts in half. Can you log desired A/F ratio or g/cyl? Do either of these change at 5000 rpm too? I don't know if fuel trim cells work the same on the 3.8, but is it kicking out of power enrichment?

 

On the Turbo Buicks it happens all the time in stock form. The ECM MAF counter wraps around its max value and the MAF reading gets hosed. The MAF counter wraps around at 255 g/s and you wind up getting something 5 g/s instead of 260 g/s and you get 6 g/s of fuel and then engine basically stops running briefly. Not sure if this can happen in your PCM or not.

 

Did you ever figure this out?

 

Yes, and no.

It was maxing the MAF. I put a new SLP MAF in it and I maxed that at 9+ PSI. I do Max it running 8 PSI when it's cold in the morning. We have not made a definative plan on how to proceed... I am thinking about geting my Stock MAF re-caled but that's still up in the air. I have also read there is a resistor i can remove on the SLP MAF to which makes it harder to max out? I have not investigated this much yet. Any thoughts? I'd really like to get this resolved and get her on the track. I know she's putting out more than 350 RWHP and I'm anxious to test it!

 

im wondering if you need to switch to a true ls1/ls6 maf like some of the gtp guys do.

 

Can't he run strictly speed density ( 2bar hp tuners feature)? Then the maf wouldn't be an issue.

 

i was gonna ask the same but im not sure how that would work with a v6 *shrug* would be a good investment though instead of keep throwing $300 mafs at it.

 

I have the SLP 85mm MAF that supports 600 HP. Is't that rated for more than the LS1/LS6 MAF?

As far as SD tuning, It's kinda weather dependent? Since this is my daily driver I did not want to have to carry my laptop around and change tunes with the weather, Or do I misunderstand true SD tuning conditions?

 

not sure why your maxing when im sure others have done the same amount of boost without these issues...although the new maf now works to a higher psi so obviously thats the problem just dont know why lol. as far as SD the computer has more then enough parameters/sensors to adjust with weather ie map/iat