European Cherokee, Serious charging problems :(

[scottishcherokee]

Hi all

I live in Scotland, UK and I have finally bought my dream 1994 Cherokee Limited 4.0

Anyhow, Im really struggling with the charging system.

Symptoms

Voltage accross battery 12v and slowly drops when running
Interior volts gauge low

I have replaced the alternator and battery - No luck

I have read on this forum that the voltage regulator for the alternator is internal to the engine management controller and this is potentially a common failure?

I have a Haynes manual for my Jeep but the wiring diagram is awful and doesnt even cover the charging circuit.

Can anyone give me any pointers to a proper wiring diagram so I can start troubleshooting?

Any Suggestions?

Many Thanks, Scott

 

[SteelHeadz]

PCM failure is not a common occurence. You are correct on the Charging system being controlled by the PCM. Note:
Whenever any connector on the PCM is disconnected, the ignition switch must be in the "OFF" position for a minimum of 5 seconds before connector removal.
It has been found under certain key "ON" or momentary key "OFF" conditions, when the black connector is unplugged, the PCM may attempt to write information to the EEPROM processor within the PCM. Sometimes this inadvertent write will set the target charging voltage to 0 (zero) volts. The result will prevent the charging system from charging the battery.
If this occurs, the only correction is PCM replacement.

check all the relevant connectors to the PCM from the alternator connections for corrosion and poor connections. Check the Battery temp sensor connector if equipped. If there is no other obvious reason for a no charge issue, then the only thing there is , is the PCM.

 

[scottishcherokee]

Thankyou very much for the detailed reply.. I have finally traced the problem to a blown 70A fuse in the Alt 1 circuit (this is supposed to be 60A) - Something has obviously caused this to blow in the past, so Im going to have a close look at the wiring for any shorts..

Many Thanks