94 cherokee overcharging issues

just finished installing a new altonator (136) to replace my 90. It wasn't handling loads and was causing my lights to dim. new alt is overcharging.
Yes it was tested with a DVOM. holding 14.5 at initial start, but as soon as rpm is increased it climbs to 19 and stays, have only run it as little as possible, i can hear the battery boiling after shut down and am not drivng it anywhere.

new alt is a reman. old alt is no longer here(core) and had the output terminal melted. its junk.

nothing changed but the alt. Did have to remove the brackets for clearancing. and had to unbolt the engine grounds near the coil due to aftermarket engine mount brackets.(SFR). yes they are tight again. allready checked that.

First things first.

My guess is that you have a bad alternator. Did you buy it from one of those discount auto parts store? I make it my business to never buy electronics or electrical equipment from those stores. Yea!, I know they come with a lifetime warranty but you spend a lifetime going back and forth to the store for replacements.

Having said that, the other reasons could be:

1) The field wire(negative from the PCM) and the ignition are screwed up. I
doubt that assuming the connector with those two 18AWG wires is not
damaged and are properly installed.

2) The PCM is bad. The dark green wire mentioned above is a ground wire controlled by the PCM. When this wire is grounded the charging rate/voltage increases up to the maximum of the alternator. In the case of the XJ, it is over 19 volts.

Remove the alternator and have it checked by a competent rebuilder and have them load test it. Better yet, return it to the store for another. My (personal) preference would be to return it and get a refund then get one from a Pick-and-Pull yard. They are readily available from a lot of Chrysler vehicles.

Check those two small wires for damage that could cause them to short to ground. Shorting to ground will give you the same results you are seeing now.

Typically 19 volts showing on the dashboard gauge is a connectivity issue, and 9 volts is an alternator issue ( most often worn out/sticky brushes ). PCM failure causing 19 volts showing on the dashboard gauge is very highly unlikely, and only should be considered after an in-depth and thorough diagnostic of all the battery and charging wiring, and connections. Be sure to look for battery wires with internal corrosion. I would also suspect connectivity issues, before assuming the alternator is faulty.

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I checked all connections and they were fine. Just swapped in a spare 90 amp oem alt. Works fine charging 14.5. Defective replacement part. Now to wait for the replacement

Interesting, must be some kind of internal short circuit.

not a regulator issue?

denverd1 said:

not a regulator issue?

Click to expand...

Regulator is inside the PCM.

techno1154 said:

Regulator is inside the PCM.

Click to expand...

The PCM controls the ground side of the field coil, so most likely the alternator had the ground side of the field coil shorted to ground inside the case.

good to know. thx guys