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Timing Erratic at low RPM - LS7 E38 ECU

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Hey Guys,

Currently trying to fine tune the VE table in Speed density mode on my LS7 c6 z06.

It has a fully upgraded top end and every bolt on possible without modifying the short block

Has a custom grind cam from Greg Good that specs are not given, but i was told it is near .700 lift. It should be similar to a texas speed 4.2 LS7 cam.

Anyways, the car has gotten better (i know it is lean at the bottom but still investigating why it richens up at the bottom end while driving) driven open loop and in Speed density. However, i have looked at my timing tables and even matched the lower rpm and cylinder air mass areas to have the same timing to prevent the ECU hoping from different timing tables and causing the erratic timing. It is roughly from stop @ low TPS % and will cause the car to buck and surge. The timing will go from low 30's to sometimes single digit timing.

Is there an adder or table that i am missing? if i get this fixed, this will make the car have great street manners (other than some idle hunting when it is hot, shut off, and turned on again).

Help will be greatly appreciated.

Attached Files

I'm sorry i don't have my tuning laptop on hand right now so I can't look at the log file. What I suspect from your description is that you may be running into issues with the idle ignition control. Irrespective of the ignition timing tables, the adaptive ignition timing will advance and retard the timing seemingly erratically in order to control idle speed. This works well with a stock camshaft but it tends to be overbearing when you have a more aggressive cam as it tries to fight against the natural lope of the cam. You'll find these tables under 'spark' - 'Advance' and then you're looking for Idle Adaptive Spark Control. There are a set of tables for over and under speed. I'd suggest you could start by multiplying the relevant tables by 0.5 to halve the effect. There are also separate tables in this same area for base idle spark and Idle adders so these may also be influencing the driveability.

It's important to be realistic with your expectations though. A large cam will negatively affect low speed driveability. I generally find that purposely dulling down the timing in the low rpm region and retarding the timing signficantly from MBT can help smooth the natural lope of a large cam at the expense of torque and fuel efficiency. I normally only need to do this just off idle and you should be back to MBT by the cruise region so the fuel economy doesn't get hit too hard by doing this. Lastly, the driveability will be worse with a manual trans compared to auto as the torque converter tends to absorb some of the lope.

I hope the above helps.

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