Hot start leaning out $12p

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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Hot start leaning out $12p

Postby Makeitreal81 » Thu Jun 23, 2022 11:24 pm

So I've figured out most everything in $12p, but when I first start it will run good say 13.5 to 1 or whatever I tune it to. Then let's say I run into a store or whatever and come out it'll run way lean like 16-17 to 1 I've tuned it to a balance, but this leaves it running rich for the first start up and a bit lean after. There has to be a parameter that changes after shut off and restart. It's not the regular temp cause it'll stay in that mode for that first start over 45 mins (drive to work) and won't change till shut off and restarted. This is on the US 165.

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Re: Hot start leaning out $12p

Postby vlad01 » Fri Jun 24, 2022 1:19 pm

Unfortunately 12P nor any of the map based ECU cals had anything for hot start compensation but if you look at 12P BLCD v6 bin and search for the inverse temp term table, there you will see how Holden bandaided the problem. At the high temp values the graph falls off abruptly into the max negative temp range if I recall correctly. So when the engine is hot beyond the normal operating temp set by the thermostat and rad fan, typically seen in hot start heat soaked conditions, it fudges the AFRs to be much richer, bringing it back inline with the target AFRs that are set elsewhere. Once the engine is running and settles to the normal heat distribution it is back in the normal non fudged areas as per normal.


You will need to make this table/graph according to your engine's operating heat range and so a bit of trial and error will likely been needed.

Hope that helps.
I'm the director of VSH (Vlad's Spec Holden), because HSV were doing it ass about.

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