Do I need a new PCM?

[cjbajb]

1997 cherokee country with 4.0 auto 4x4. Transmission doesn't always lock up torque convertor, cel doesn't always come on when you turn key on, electric fan comes on as soon as you turn the key on and voltmeter and fuel gauges are hit and miss. Anyone else have these problems that could give me answers? :bang:

[LizardRunner]

That sounds like it might be the ignition switch going bad.

[Mudderoy]

1997 cherokee country with 4.0 auto 4x4. Transmission doesn't always lock up torque convertor, cel doesn't always come on when you turn key on, electric fan comes on as soon as you turn the key on and voltmeter and fuel gauges are hit and miss. Anyone else have these problems that could give me answers? :bang:

I think you may have more than one problem there.

Yeah I guess all of them except the torque converter could be the ignition switch.

[cjbajb]

by the ignition switch, I am assuming that you mean one mounted on the column under the dash? Also I checked the alternator at the battery and it is charging about 15.5 volts. Is that too high?

[ParadiseXJ]

by the ignition switch, I am assuming that you mean one mounted on the column under the dash? Also I checked the alternator at the battery and it is charging about 15.5 volts. Is that too high?

What does the dash gauge say. Is it past the center line? 15.5 sounds too high to me. Actually I'd be a bit alarmed if mine was 15.5. Even with a new alternator and battery, the most I've seen from any one of my vehicles was about 14.9. That was on my Nissan, and the alt went south shortly thereafter. None of my Jeeps have ever gone past the center line except when my alt had a bad VR...and then it was just a hair past the center line.

I have two identical DMM's, they don't ever read the same.

[cjbajb]

when the gauge on the dash works it only goes to 14 at the most. I have 2 multimeters and they both read over 15 at the battery. If the ignition switch was out would it cause the jeep to die? It will still turn over but won't fire.

[Mudderoy]

by the ignition switch, I am assuming that you mean one mounted on the column under the dash? Also I checked the alternator at the battery and it is charging about 15.5 volts. Is that too high?

I guess the gauge could be reading wrong, but 13.8 volts (about 14 on the gauge) would be normal. You might have a voltage regulator issue. Best to put a volt meter on the battery and double check.

[89Laredo]

Isn't the 97+ alternator regulated by the ecu? Iirc renix is internally regulated but after a certain year the computer does it.
I have a 97 computer. 280k, 50 bucks + shipping.

[Mudderoy]

Isn't the 97+ alternator regulated by the ecu? Iirc renix is internally regulated but after a certain year the computer does it.
I have a 97 computer. 280k, 50 bucks + shipping.

Really? I thought the regulator would be too big to be in the ECU, figured it was in the alternator like the Chevys were way back when.

[89Laredo]

Ill post a fsm quote when I get home if I can find it.

[Mudderoy]

Ill post a fsm quote when I get home if I can find it.

Good cause I'd like to know for sure.

[cjbajb]

Everything I've read on it says the regulator is in the PCM. But there are 2 or 3 different PCMs for 97 also. The one I have was replaced about a year ago but has no part # on it. Any ideas on how to know which one I have?

[89Laredo]

CHARGING SYSTEM OPERATION
The charging system consists of:
² Generator
² Electronic Voltage Regulator (EVR) circuitry
within the Powertrain Control Module (PCM)
² Ignition switch (refer to Group 8D, Ignition Sys-tem for information)
² Battery (refer to Group 8A, Battery for informa-tion)
² Battery temperature sensor
² Generator Lamp (if equipped)
² Check Gauges Lamp (if equipped)
² Voltmeter (refer to Group 8E, Instrument Panel
and Gauges for information)
² Wiring harness and connections (refer to Group
8W, Wiring for information)
The charging system is turned on and off with the
ignition switch. When the ignition switch is turned to
the ON position, battery voltage from the powertrain
control module (PCM) is supplied to the generator
rotor to produce a magnetic field. This is done
through one of the two field terminals at the rear of
generator. On models of previous years, battery
voltage to this field terminal was supplied
directly from the ASD relay.
The amount of DC current produced by the gener-ator is controlled by the EVR (field control) circuitry
contained within the PCM. This circuitry is con-nected in series with the second rotor field terminal
and ground.
A battery temperature sensor, located in the bat-tery tray housing, is used to sense battery tempera-ture. This temperature data, along with data from
monitored line voltage, is used by the PCM to vary
the battery charging rate. This is done by cycling the
ground path to control the strength of the rotor mag-netic field. The PCM then compensates and regulates
generator current output accordingly

[cjbajb]

Ok, I've replaced pcm and ignition switch. It now starts fine and idles but still overcharging. Any suggestions? :bang:

[Mudderoy]

Ok, I've replaced pcm and ignition switch. It now starts fine and idles but still overcharging. Any suggestions? :bang:

Any codes? I wonder if the temp sensor below the battery is working.

[cjbajb]

No codes but I don't run it for very long either. I don't want to ruin the battery by overcharging it