I found out that an issue that I thought was my transmission dragging is actually a tune issue. I noticed after putting in a higher-stall converter that there was a sudden "free-up" feeling after a cold start. And here is the reason:


There is a 20 degree jump in spark advance right before (about 1-2 seconds) before it indicates that it enters closed loop. This is a 100% stock AUJP apart from inverting the 4th gear switch bit for my model of transmission. What would cause such a drastic jump in the spark advance? I'm guessing it is using different tables for closed loop, but is there something that is off with the engine that I could look at? It seems odd that they would program that much of a jump into it stock. The engine is a rebuilt 350 TPI with Bosch III injectors, but that's about all that should be different from stock.

So great tuning gurus, is this a case of needing to adjust something on the engine, or am I going to have to do some tuning of the prom?

 

From several threads, it looks like it might use the 100 kpa column of the Main SA table until it hits the 113 degree threshold. At the point right before it changes, the 100 kpa column has 18* of SA, and 37* at the actual 40 kpa that it is seeing. So I suppose it's working like it's supposed to, but still seems very odd to me. Do people just deal with this weird behavior, or is there a way to "fix" it?

 

Change the value at $8031 to -40*. ECU/XDF dependent it may be this entry: "Spark Advance Cold Disable Temp."

RBob.

 

Are there any downsides to doing that? Why does the stock ECM even have it set up the way it is?

 

Not that I know of. Easy enough to try it and change it back if it causes other issues.

I have no idea. It worked OK on a stock setup. There are some other oddities in the $8D calibrations that cause issues with modified engines.

RBob.

 

Damn you Rbob!

I put my ECM back up under the dash thinking I was done with the tune... now I'm going to have to pull it back down again because I'll never be able resist making this change!

 

Could adjust the table so it is not so much of a change.
You don't do much 100 Kpa at idle speed areas to worry about disabling it IMO.
Its a user choice how to deal with it.
Jp