91 250 cpu location
 

does anyone know the location ot the cpu 1n a 91 b250 ramvan?
i think the regulator is blowm
thanks

Above the engine on the firewall.

Check for a fuse link or in-line fuse that may be behind the brake booster, some have found that to be blown when the alternator would not charge yet tested fine.

actually i found it under the glove box..any suggestions on overiding the cpu and using an older external regulator to charge the battery?

Can't be done reasonably. If you bypass the regulator circuits within the PCM you will have constant charging and check engine lights on the dash and your battery gauge will not work.

That is the RWAL brake control module, not the PCM.

The PCM is located under the hood, not inside the dash. My Haynes manual shows that all PCM's for vans will be located above the engine on the firewall.

yup you were right...had everything working fine, full charge etc.. then it started again w the discharge..anyy luck on overriding this so the battery charges? dont want another pcm if its gonna do it again.....any one have a precise wiring diagram?
thanks so much

Did you replace the PCM and the problem returned? I would have the alternator rechecked for I have seen some that had intermittent problems. I would recheck the alternator first and then the wiring. I doubt the PCM would be causing this problem.

Here is the charging circuit diagram:
Attachment 102491

I've been where your at right now. Do not blame the ECM/SMEC yet. Find the fusible link. Follow the fat wire that goes from the alternator to the battery. Behind the brake booster will be a fusible link. Grey I think.

Mine did not stretch out when pulled and actually had continuity, but replacing it fixed my charging issues.

If you just replaced the alternator and it worked for 15 seconds or so, then quit, you have overstressed the new unit, by asking too much of it before the brushes have had a chance to break in. You asked too much by expecting it to charge a depleted and possilbly old/ sulphated, abused battery.

Always fully charge the battery when you replace an alternator, especially a rebuilt one.
Do not ever expect your alternator to fully charge a depleted battery unless you are driving 400 miles on the highway. At Idle speeds the output of most alternators is pathetic.

If you are sure the fusible link is good, then with a fully charged battery, and the engine running, tap the alternator lightly with a hammer. This might allow the brushes to reseat on the armature.

Frequently testing of alternators does not indicate a problem if there is not significant load on the alternator. A significant load is a depleted battery that barely has enough juice to start the engine.

If you decide your computer is at fault, don't try an external regulator, goto rockauto.com and get a rebuilt ECM from Cardone for about 170$. Open up your old unit and check any numbers you find against the part numbers listed. There are 2 different circuit boards encased in silicone. The numbers you are looking for are under the top circuit board.

Do not rely on the Ammeter on the dash to tell you if it is charging, use a Digital volt meter and hope for voltages well above 13.4.

Update us as you figure things out.

no i didnt replace the pcm, as believe it or not i hit a bump and the check engine light went out and the voltmeter started telling me we were at around 14 volts. this happenned for two days and then knowing that it was too good to last i started pulling on those fusible link wires, then blammo right back to were i was....i know i should have let it fixed itself and walked on eggshells...kissedf it and maybe a wax job would help?

also no fuse on fusible link..and thanks so much for the diagram..wont stop on this qwest till i figure this out even tho i might lose whats left of my knuckles and my mind.....