teach79

Hi all, I could use anybody's two cents about my tune issues . The stats 02 z 406 ls2 callies internals afr 215 ported heads fast 92 intake 11.5 to 1 compression yella terra roller 1.7, tpis zl17 cam which stats are 252/252 610 lift 112 lobe separation . Full exhaust with 1 7/8 primary headers . The issue is that the car is loading/over fueling on idle to the point where I lose a cylinder or two till I go drive somewhere and stand on it ? Second issue is that the car does not start well when hot or cold and I have to step on the gas pedal while cranking to get it to start and keep it running for twenty seconds till the car takes over . The car has been tuned, I just got the car back and all these issues are happening ? I am bringing the car back to the tune place soon but can anybody give me some detailed things I should be asking the tune guy about ? Does anyone else have my same engine stats ? If so how was it to tune your car ? I have a ported ls2 t body that the tune guy thinks is causing issues so I am switching over to a aftermarket 90 mm t body set-up what do you guys think about that ? Would love to chat with someone who has my same engine stats and ask questions . Btw when i am driving the car or if I am on it the engine performs really well and feels great 520 to the rear wheels on the dyno ? Thanks

tblu92

Ist of all you did so many modds at once that it takes may hours of data logging to see where to correct the issues--
Your LT headers are your biggest challenge--The new front 02 locations will give your ECM erroneous 02 data--To correct you must lower the 02 switch points--so they hover around .450 millivolts-- Once you do that --- try and get your fuel trims in the slightly - or "0"area and it will make it much easer to tune

teach79

Thanks for the info . I bought the car with the motor set-up two years ago the only thing I have recently changed was the cam that's it . The car used to have a 232/232 600 lift 114 seperation. With the old cam I was done making power at 6300 ? I wanted more ? The issues that I had with the old set-up and tune was that it would surge once in awhile when it was hot out and also load up on idle . But was never as finicky as it is now . I work on cars for a living and have had this car down to bolts and I understand automotive computer terms and readings . I am not a tune guy nor have I ever tuned a car which is why I am asking so many questions your last post makes sense and I will ask my guy about it . If you or anyone else has ideas I would like to hear them . Thanks

BLKTA

Going from 4 degrees of overlap to 28 degrees is a huge jump and will require a complete retune from idle to WOT. Was the car tuned locally? If so, I would bring it back to them for a retune.

teach79

It was done locally and on a dyno . I don't want to bash the guys doing it cause I like them but I just want the car a whole lot more streetable . I figure I need to educate myself a bit about tuning so I can hopefully ask the right questions . Thanks for the help so far guys .

BLKTA

Understood. Based on your location, I'm pretty sure I know who it is.I'm in MN and could help you if you have the tuning software. Do you have a wideband oxygen sensor? If not, you need that as well.

tblu92

Large overlap cams although they make more power upstairs are notoriously dirty at idle
Overly rich is common---Take many adjustments in the tune to correct cold start and warm start issues as well as idle hunting surging or dying---If its rich at idle add some % to the desired airflow start with 10%---Also you have to trick the ECM on a cold start to get it to start normally---Done by commanding a lean 15.0 to 16.0 in the open loop normal tables to lean it out---( it won't really be running that lean but will end up around the stock 14.68---
After it is warm and switches to closed loop---lowering the 02 switch points will again trick the ECM to get it back to 14.68 to correct P/T richness

teach79

Thanks a ton for the info . What you said makes sense to me and I will talk to my guy about it when I see him this week . The car will be re tuned once the 90 mm t body is installed . For the record I am aware I put a large cam in the car and that go fast parts are all about give and take . You don't get bigger hp numbers on a na motor without giving up some driveability and idle quality . To be fair I have met a few c5 vette guys with larger or same spec engines and cams as what i have and they are not experiencing half the issues I am ? Which is the reason for my frustration . The car is a blast to drive above thirty mph but stop and go and starting the car got or cold is a pain .

06x6spdGTO

Ditch the LTFT's Completely...

Only run STFT just off Idle.. and tune it with a wideband. You can hack at it by putting the car into PE mode at IDLE and commanding Stoich in the PE table. With larger camshafts and Longtubes the exhaust pulse from the cam overlap can cause the car to load up.

Other than that your tuner need to get your VE table dialed in and then work on the MAF sections..

teach79

Thanks a lot once again that makes sense to get rid of lt ft but I did not know you could do that ?

tblu92

I agree---DISABLE the LTFT's is a good thing on a large cam to aid in idle hunting and issues that you are having--There is so little vacuum at idle and low RPM's that the fuel trims seem to bounce way positive and then way negative uncontrollably--Make sure you set the PE MAP threshold higher as well--See what KPA your eng idles at--My guess is around 70-80 KPA---Set the threshold a little higher otherwise the PE can be activated at low RPM or even idle !! RICH RICH RICH