LS3 GMPP hot cam (idle and surging issues)

[adamg]

Does anyone have a better file than the one gm sends with their computer? I lowered the idle so the customer doesn't have to buy brake pads every week. It still tries to die right when you put it in gear. It has a 4l65e auto with a TCI standalone trans controller. Funny thing though once you put it in gear the first time and it tries to die, if you dont turn the engine off it doesnt try to do it again, until you turn it off and restart it? Also it surges while driving at normal speeds (under part throttle) GM with the paper they send with the engine says it is normal? We have done lots of LS engine conversions, and we have had bigger cams than this that dont surge at all. I really would like to lean on some of you guys that have done these gen 4's I have been around these engine since 97, and this is the first drive by wire i have had to tune. You can look at our (half of a website) spankysrodshop.net to see some of the work we do.Any help would be great thanks!

[69lt1bird]

Posting a log and tune if you want help. Also, does it have a higher stall converter? If not, that will do it.

[adamg]

it has the factory stall. So you think a stall would help the surging? I understand the principal of getting the rpms up higher, but again we have had other engines with low stall converters and big cams and they didnt seem to surge this bad.

[69lt1bird]

Any cam that is going to give you power will pull against the stock converter. A 3000-3500 stall will be loose enough to allow the higher RPM's that the new cam needs to idle at and stop loading and unloading the converter.

Obviously is needs to be tuned right in the first place but a tight converter will add to the problem.

[midgetracr]

I have a GMPP LS376/480 kit engine in a small sports car. With the stock tune it surged a ton from idle thru about 70 MPH.

If you are using the Hitachi credit card style MAF sensor, I think this sensor is very sensitive to inlet tract shape and turbulence. My surging problem was solved by installing straightening vanes a couple inches upstream from the sensor in the inlet tract, tuning MAF and then VE via ktoonsez' EQ-VE software. The engine is now able to drive my 1600 lb. car thru a parking lot at 5 MPH and cruise at any speed without surging.

[adamg]

I recentley started using the program posted for VE in later ecm's I am trying to figure out if i am using it right? I have a E67 ecm and i have taken my program and opened engine/airflow/speeddensity/(constant),(map2),(map),(maprpm),(rpm2),(rpm), also engine/airflow/dynamicairflow/ (zonerpmboundaries),(zonemapboundaries). I can generate a VE table but I dont know what i need to do to fix it? I have a FAST wideband, but it is not connected to my hpt cable, do I just change the numbers in the grid according to my a/f ratio with fuel trim disabled? Do i add or subtract from the numbers to change fuel trim? and do I need to disable my MAF?

[midgetracr]

Suggest you search for posts by ktoonsez and read, read, read

[81commodore]

Any Luck with your set up ADAMG ? I have just finished the same 376/480 with 4l65 combo and suffer the same problem?

[Christian GM]

Suggest you search for posts by ktoonsez and read, read, read

me too!
I did it at least 3 times

[65BISC]

I'm not a tuner, but I found this post about these motors and computers. I just had the LS376/525 put in my 65 Biscayne mated to a 4L65e and am having some issues. the shop that did it is turning out to be not so trustworthy so I don't trust the answer they are giving me about the problem I'm having.

Problem: At lower RPM with some extra throttle, the engine seems like it is misfiring. It doesn't smooth out until close to about 3000 RPM. When it's running at light throttle it's fine, but when you give it a little more just before the tranny downshifts, it bogs a bit and you can hear it missing slightly, but then when it gets better as the RPMs rise to 3000 and above. WOT is fine and runs strong. The shop said they called GM and they told him the computer is still learning and still breaking in and to keep driving and follow the break-in instructions. I have put about 200 miles probably on the car so far and it's still doing the same thing. It just doesn't make sense what he is telling me, but wanted to see if anyone could help me that has experience with this similar motor/trans combo.

it does lunge a little, but my main issue is the "mis" at that mid throttle between 2000-3000 rpm.

thank you!