I want to reset the computer on my 1988 F150 302/AOD truck--how long do I need to disconnect the negative battery lead for it to reset itself? I am thinking 10 - 15 minutes, but is that long enough?
And then, how long does it take for any codes to register after that?
thanks for any advice.
Frank.

 

10-15 minutes should be good. Codes register whenever there's a problem. So they'll register immediately if there is a problem present immediately. You can also clear the codes by disconnecting the ground while reading the codes. That way you don't have to reset your clock and radio stations.

 

qman, what ground? , thanks

 

The jumper used to get the computer to run the self test. Just pull it out while codes are being flashed and it will erase the codes.

 

Thanks for the info.

 

10 seconds.

Disconnect the battery, turn on the headlights, count to 10, turn them off, reconnect battery. Done!

 

turn on the headlights??

 

^^^It helps remove the residual power from the computer.

 

if there is no power to the system how can the computer still have residual power?
is the turning on the headlights to 'drain' the system?

 

Yes it does.

 

disconnect the battery cable for 30 seconds will do it.

 

The computer has capacitors in it, and can usually sustain itself for 10-20 seconds, however, I have seen some stay alive for up to 5 minutes.

 

The ford computers have a capacitor where the battery (memory) lead enters the computer. Capacitors store electricity. Not a whole lot, but enough that if your battery dies, the computer can retain its memory for a few minutes while you jump your truck.

By disconnecting the battery, and turning on the headlights (which won't light BTW), you're draining that capacitor. Actually, the instant you do this the computer is dead, you really don't need to count to 10. I just put that there for good measure.

The Ford computer, the EEC, is fairly sophisticated and "learns" about your engine as it wears out over time, which they all do. As the compression lessons, the injectors start to clog and stick, the valves tap and don't open all the way, the EEC figures all this out on the fly.

By disconnecting all power and draining this little in-computer capacitor, the computer because "factory stock" and loses all the learning that it's done. In most cases this doesn't really matter as the computer can relearn everything reasonably quickly, but on a really high mileage, tired engine the first start is "interesting" to say the least.

I recently swapped out my EEC on my '93 300K+ crewcab and I tell you, the new computer was really confused. Timing jumped all over the place, idle kept hunting between 450-900 RPM, sounded nasty for a few minutes until things stabilized and my EEC realized how tired my engine really is.

 

Another thing you can do is touch the negative battery cable to the positive cable when you remove it from the battery. This will discharge the capacitors in the PCM.