ECU and disconnecting the battery - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

Evil Roy · 08-15-2003, 23:39

I've seen from the manual that you should ensure the ECU memory is kept intact while you disconnect the battery.

If you don't, what IS the result? Does the ECU need to be "reprogrammed"?

Specifically, a 1989 EA 3.9 MPI.

Thanks.

Aussiblue · 08-16-2003, 03:40

It will relearn in time but it may be difficult to start plus if its a four speed auto you will need to reset the transmission. Just go to an auto parts place and buy one of those things that allow you to plug a 9 Volt battery into the cigarette lighter. Of course if you have a battery backed alarm system like I have you'll find the alarm battery will also keep the ECU memory alive.

b-juggles · 08-16-2003, 23:41

aussie blue, why does tranny need resetting?

and how is it done?

Soxx · 08-16-2003, 23:47

It is quite ok to disconnect the battery.
All what happens is the ECU needs to re-learn the current status of the engine, as certain variables change as the engine wears.
This will only take a 100 or so k's of driving.

Rick.

mongrelEB · 08-17-2003, 05:01

It'll run fine if you disconnect the battery, as Soxx said it will only forget the minor things, mostly to do with compensating for engine wear. Takes very little time to relearn it.

Aussiblue · 08-17-2003, 07:45

To clear and reset throttle calibration with ignition on engine off go through the following sequence:
Manual 1
Switch to economy
Manual 2
Switch to performance
Manual 3
Switch to economy

mongrelEB · 08-17-2003, 16:49

I ws under the impression the throttle calibration was only needed for the integrated engine/box computers?

Aussiblue · 08-17-2003, 23:17

No; it's needed for all M85/95 ECU.

mongrelEB · 08-18-2003, 04:22

Well I've never done it in EAs/most EBs and the shift schedules haven't been affected.

Aussiblue · 08-18-2003, 04:27

Work in my NB (never tried the NC).