What exactly do the ECM's DMFACT and DMALDL modes do? (Page 1/1)
Romsk JUL 30, 08:44 AM
NORMAL is when pins A and B are open, this is what is used normally when we drive.
DMDIAG is when pins A and B are shorted, this is just for use with ignition on but engine not running. It causes the SES light flash error codes.
DMFACT is when pins A and B have (if I recall) 10k Ohms across them.
DMALDL is when pins A and B have 3.9k Ohms across them (I may have the resistance values reversed).

Regardless of what resistance is used to get into the modes, what exactly do DMFACT and DMALDL modes do?
Are they just for ignition on? Or are they for running the engine too?

I know that the Fiero does not run well in one of those two modes but I forget which. I am just trying to understand what those two modes do.

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Paul Romsky

fierofool AUG 02, 11:24 PM
With A and B shorted and the engine running, the ECM manages the engine without sensor input and at no advance, other than the mechanical advance achieved by turning the distributor. This is to set base timing at about 10*. Once the engine is turned off, the jumper removed and restarted, the ECM takes over using sensor input and electronically advances the timing as needed based on comparative tables of the throttle position sensor, coolant temperature sensor, etc. Do not insert or remove the jumper while the ignition is in the ON position.