Coolant Temps, ECU, and Timing Retard

[DSMtuned]

This questions is actually for Carl, since I know he knows. ;) We talked about this years ago.

Carl, at what coolant temperature will the 1g ECU change the timing map and start to pull timing?

Thanks!
-Craig

[Carl Morris]

Uhhhh....hrrmmmm....well [cough]...if I ever knew, I don't remember. I'll ask the dsm-ecu list :-).

[DSMtuned]

Uhhhh....hrrmmmm....well [cough]...if I ever knew, I don't remember. I'll ask the dsm-ecu list :-).

Doh!:D I know we talked about this sometime.;) That would be great if you could ask and let me know.

-Craig

[Carl Morris]

Not sure why confusionisbad deleted his post, but the dsm-ecu list confirmed that for 1g there is no retard based on hot coolant temps, but there is a bit of retard for cold coolant temps. There IS retard at both ends of the scale for intake air temps, as was posted.

"There is also an 8 byte table at 7EA0 that does timing adjustments based
on Intake Air Temps. This is where hot temps hurt power. Again, 81=+1, 80= no change, 7F = -1.

Stock code is:
7D, 7F, 80, 80, 80, 7F, 7E.
where temps are:
185, 133, 100, 73, 48, 19, -14"

[confusionisbad]

Yeah Carl, After I posted that info I realized it didnt pertain to coolant temps for 1g's, just air temps. If you wish I can repost it, since it was good useful info.

*Edit* Here is what I posted in my previous post

Per DSMLink Forum:

The ECU will not update long term fuel trim values (called "learn mode" in the first post of this thread) under at least the following conditions:

2G: coolant < 179F, intake >= 133F, baro < 22.9 inHg, baro > 31.6 inHg
1G: coolant < 190F, intake >= 123F, baro < 22.9 inHg, baro > 31.6 inHg

The ECU will force open loop mode under a zillion different conditions, including the following.

2G: coolant < 51F, coolant > 228F
1G: coolant < 87F

Dave has already covered fan operation on 2Gs. I'll quote here again for completeness. At speeds less than about 45 mph with the A/C off, the radiator fan will be switched on low at 210 and off at 203. Under all conditions the radiator and A/C fans will be switched on high together at 224 and off at 217.

Fan operation on 1Gs, of course, is not ECU controlled.

The 2G code includes a manual (as opposed to table based) reduction in ignition advance that does not appear to be present in 1G code. This pulls a total of one degree of timing at 206F or a total of two degrees at 224F (they are not cummulative).

Intake temperature will also cause a reduction in ignition advance. The tables are laid out like so, with interpolation occuring between the points.

2G intake air temp ignition advance adjustment:

185F = -3°
132F = -2°
100F = -1°
73F = 0
48F = 0
20F = -1°
-23F = -2°

1G intake air temp ignition advance adjustment:

185F = -3°
132F = -1°
100F = 0
73F = 0
48F = 0
20F = -1°
-23F = -2°

Whew. OK, hopefully that's enough for now.

Thomas Dorris

[DSMtuned]

Not sure why confusionisbad deleted his post, but the dsm-ecu list confirmed that for 1g there is no retard based on hot coolant temps, but there is a bit of retard for cold coolant temps. There IS retard at both ends of the scale for intake air temps, as was posted.

"There is also an 8 byte table at 7EA0 that does timing adjustments based
on Intake Air Temps. This is where hot temps hurt power. Again, 81=+1, 80= no change, 7F = -1.

Stock code is:
7D, 7F, 80, 80, 80, 7F, 7E.
where temps are:
185, 133, 100, 73, 48, 19, -14"


Ahha! So the high intake temps are what retard the timing. Thanks for researching and clearing that up for me!

-Craig