Hi everyone. I've got an unusual problem that I just can't get a hold on and I know it's something extremely simple I'm just completely over looking. I've already searched on here and other places for answers, but just can't find anything to fix my problem. To begin with the vehicle in question is a 2010 ls3 corvette that has had an ls2 APS twin turbo kit installed onto it. I know this may not be preferred, but this was what was sold to us at the time. The kit came with an already retuned ecm that was supposed to be easy to build off of, only the tuner that did the tuning, well lets just say I'm not sure if he even knew what he was doing and leave it at that... The kit came to us with the LS2 injectors, wrong for the LS3 I know, so the shop it was purchased from sent us the correct shorter 60lb/hr injectors. Ever since day one this thing has surged. It was given to me to me to fix and it just seems that I just keep beating my head against the wall over this thing. Once I get it fixed, I'll fire it up cold and it's right back to where it was before making any attempts at fixing it. Here's what I've gotten it down to or atleast seen happening. I can watch my o2's switching voltage (going rich and lean as they should for the cats) and the engine revs up and down with them. My a/f isn't even where I would like to see it. It too switches from 14.1 to 15.1 with an average of 14.6, which is where I would like to see it, but I don't like it (free ranging) that much. I originally just thought it was the fact that the tune was originally set up for the taller 60lb/hr injectors, so I entered (using Greg's injector data) the shorter 60lb/hr injector data. I even installed a correct map sensor out of the supercharger of a zl1 for the boost (which the original kit did not come with). Initially this cured all of the surging, until I put the car into speed density, then every bit of it came back just as bad as it was before entering the correct injector data and whether it's rich, lean, perfect, nothing matters - it still surges.
The best things I have done for it, which kind of goes against the usual ways of thinking, are to really advance the ignition timing in the idle area, increase my ignition over and underspeed settings, lower my idle to 650 (this was so the turbo's don't free spoil as easily) and finally the single best thing I've done is turn my transient fueling "way" down. In fact if I remember correctly I think I multiplied the mid section by .05 then zeroed out the really lower vacuum numbers. The transient fueling was without a doubt the best thing I have done, but this also made it run richer when first starting the engine as you will also notice in the datalog. Now instead of idling up and down in a 50 to 300 rpm area, it idles in a 25ish rpm area. In fact watching the tach in the car, you can't tell its changing at all, but the tach on the dyno shows it and the exhaust notes changing are the biggest give aways. There has got to be an airflow number that I'm just not aware of being able to adjust on this that will compensate for the added airflow of the turbo's at idle and fix all of my problems thus allowing me to get my questionable fueling back in line. Any thoughts on this? Also let me say ahead of time any and all help is greatly appreciated. I've attached a datalog demonstrating the surging higher in the rpm's and if you bring up a tach display with the 02's and long term fuel trims you should be able to see what I'm talking about at idle. The jeff tune is the original tune from original tuning shop with the closed loop turbo vette being the one I'm currently working off of. If you see anything at all out of place or know what I need to adjust for the added turbo's please don't hesitate to let me know.
I know the tune is rather hacked up with things I've tried with no success. I was going to fix these before I went back to correcting everything right after getting this surge problem sorted out.
To date, I've tried adjusting injector slopes, stoich, MAF and VE tables, O2 settings (for ease of tuning and to try to force it to run closer to a 14.5 af ratio-will adjust switching back to stock once done tuning), open loop EQ's (because once I got it gone hot, it was back cold-this just made things worse), injector timing (did mainly to get rid of fuel igniting in exhaust instead of combustion chamber where it should-a found side effect of extra airflow from the turbos)(also returned to stock just to make sure this wasn't causing side affects-actually got worse at stock), proportional idle, adaptive idle, integral idle, iat's (did this because I noticed it also got much worse with the colder denser air-was 38 degrees fareignheit out), then a couple I'm sure I forgot that you will notice.
Sorry for being such a long winded post, but I figured the more info, hopefully the easier it would be to see.
Thanks,
Greg