negative timing on Idle

[C10_ustacould]

Tune your MAF perfectly
Tune your VVE perfectly
(these two alone may be enough to get idle right in a mild application, don't assume you need to get crazy with torque tables)

Spark and Min Spark need to be not stupid, do not try to force it to idle with a certain amount of timing. Many cars and trucks idle with 5 degrees of lead, of course you don't want -15 but 15 is also not mandatory.
Zero Pedal External Load Table needs to more like zero pedal torque, log it
Airmass and MAP Coefficients BOTH need to be adjusted properly depending on what you have done to the car, typically only with a cam swap or the like major change.


many people do not tune VVE, MAF is off and before taking care of that they chase torque model adjustments with no change.....fueling must be correct or spark will be wrong and fluctuate, etc.

when in doubt, go back to stock and start over (regarding idle).

What if the negative timing is throwing it into a default map, can you still tune the MAF first?

[cmitchell17]

We have a 6.2L/8L90E with TSP VVT-1 cam upgrade. The long block is a 2018 and the trans is a 2015, we are using a 2015 ECM/TCM and an aftermarket harness (the fuel sensor and the Lt bank injector harness have been swapped to match the 2015 configuration). We have seen as much as -29 degrees timing at idle and it is throwing it into a default map. Local tuner is very experienced in LS tuning and has a good amount of experience with non-swap gen v tuning. Our swap is a '67 C10 and we are stuck, need to resolve this negative timing issue so that we can get started with tuning the MAF. I will include our current tune file along with a very somewhat long log file, would greatly appreciate any assistance offered. Attachment 99145 Attachment 99146

Pull up the virtual torque editor, I would start by pulling 50ft-lbs from the -10 degree spark table, then 40ft-lbs from the 0 degree spark table, and do that for the rest of the tables until you get to the 30 or 40 spark table and don't take anything out from that. Only take out the torque from the idle airflows (.1-.3 grams/30-70MAP) and at idle rpms (<1000rpms).
You might be able to take a little more torque out in the idle cells if that doesn't pull timing up enough but eventually if you take out too much the idle will start to osciallate.

[cmitchell17]

What if the negative timing is throwing it into a default map, can you still tune the MAF first?

What I believe is going on here is that yes we may not have fueling correct, but not because we haven't tried but because with the available tools we have (widebands) we just can't accurately look at wideband feedback (excess oxygen in exhaust) to correctly state weather we are lean or rich. Especially with larger aftermarket cams which have excessive overlap and EGR effect which just screws with combustion so much to where we really don't know whats going on, and the fact its at very low RPMs at idle makes the problem worse, and the suboptimal timing at idle (because of speed and torque control) makes it even more worse.

Try to reduce the virtual torque tables in the idle cells and see what that does and report back. That has worked for me on my TSP 228/236 114 cam but only partially, It will bump up timing to a more reasonable 15-20 degrees but it still rapidly spikes and swings up and down which leads to surging, bucking, and vibration.

[C10_ustacould]

Will try it and report back.