Another lesson following the starter failure.
I can only comment on my LS3/480 on the following but I believe these principles apply in a broader engine spectrum, so take it for what its worth. I noticed before the mechanical starter failure the LS3 struggled a little to start after “heat soaking” following a drive. It would start, but not as easily as when cold, no surprise here.
I wondered which ECU tables were heat sensitive during starting and went hunting. IAW the tuning school house, ECU table settings followed some cam spec rules, and without getting into the multi-dimensional discussion of cam dynamics, I will consider the 480 GM Hot Cam more than a mild cam, but perhaps not necessarily a “big” cam” so I extrapolated between mild and big cam dynamics. I found three tables within the GM ECU which impact fuel, air, and timing during "hotter" starts. The picture I included are my initial adjustments, not final, but getting there. Anyway the tables included:
- Cranking Spark: GM really did some odd things to the stock table. At 212 degrees and at RPM ranges in block ranges at 100 and 300, they changed the degrees from +5.0 to -10.0 and within a few RPMs back to +2 or a +3 and back to -10.0. I could not find a good rationale for that anywhere. Solution is to smooth out the hot coolant temp values.
- Idle Startup Air Flow: School house says add 10%-20% more air. I added 10% but may go back and add a little bit more at higher temps IF I still have a higher temp start concern, that I’m not satisfied with.
- Cranking FA: Again, school house says 10% more fuel across the spectrum. However, I noted something again odd by GM. As the temp progressed from cold to hot, the values declined up to about 194 degrees then climbed back up to 248 degrees. Seemed a little odd, but I went with it for now. Not sure why but this is another target area for smoothing if the startup still isn’t as clean as I want.
If you’re experiencing a stubborn "hot" start, take a look at these three tables. Not many tuners even bother. Based on my experience with tuners, the focus seems to be on power and not a wide enough ECU adjustment to get the best overall engine performance other than more HP…..just my opinion. If you want a closer look at the picture, I tossed in a PDF for reading enjoyment.
I’m sure someone out there is a lot smarter on this topic than I am, so let the discussion begin or not.