Over Charging Alternator- Where is the regulator

[ATaylor]

Hi,

Having a problem with a 1991 D250 CTD. The alternator stopped charging so we replaced the alternator. The new alternator was over charging and boiling the battery. Took the new alternator back and replaced it with a new one, but same brand. It is still over charging. It has 14. 8 volts at idle and

17. 7 at high idle speed. The amps were in the 50's at idle and well over 100 at high idle speed with no load on the battery.



1. On 1991 trucks is the voltage regulator in the alternator or external?



2. Does the PCM regulate the alternator?



3. If the PCM is the regulator can it be fixed or does it need to be replaced?



Thanks for any input that you can offer.

Archie

 

[Gary - K7GLD]

On my '91, the regulator was a small unit easily seen and replaced, mounted about dead-center on the firewall up high, towards the hood - was cheap back when I replaced mine - $12 at the dealership as I recall - and the ONLY part failure on the truck in 120K miles in 11 years...

 

[JLEONARD]

And replace that regulator quick like. . even if you get a cheap one at an Autozone ,etc. At that voltage the battery will be toasted soon...

been there with an old Dodge Dart that had the same setup.

 

[PToombs]

Is the truck intercooled? If so, the PCM does it. Does A/C and cruise work? The crank sensor may be bad,or have a bad connection. The wire comes down the front of the head, the plug there corrodes, or the wire breaks. Sensor clearance to the balancer should be . 050.

You can bypass that part of the PCM and put in an external regulator, like the older trucks have. There are several threads on here about that.

 

[cerberusiam]

Is the truck intercooled? If so, the PCM does it. Does A/C and cruise work? The crank sensor may be bad,or have a bad connection. The wire comes down the front of the head, the plug there corrodes, or the wire breaks. Sensor clearance to the balancer should be . 050.

The 91 still used the regulator on the firewall, intercooled or not. Wasn't until 92 the SBEC took over control of the charging and even then there is a possibility very early 92's used a regulator.



When the wires corrode and/or break it usually quits cherging, not over charge. Regulator bad or possibly a short that is causing the over charge. Try regulator first as they are a finicky POS at best. Check all your battery cables also for good connections. Had a bad sub feed cable one time that kept calling for more voltage and was burning bulbs right and left. Finally started pulling cables apart at the connectors and corrosiopn was all inside.

 

[ATaylor]

Thanks for the Help

Thank-you for all of your replys. I will try the regulator on the firewall first and check for corroded battery cables next. Thanks again for your quick replys.

Archie