97 tj 2.5L high voltage

[nickcoleman9]

So my friends 97 tj had all the lights and gauges flickering, she told me the radio was cutting out and it was beeping at her, so i guessed the alternator was fried, when she brought it over and i put a meter on it I'm getting 29-30 volts from the alt and the battery while running.  But gauges seem normal now and volt meter on dash reads fine. So i am figuring there is a voltage regulator that's gone, but is it internal to the alternator or is it replaceable.  Is there anything else i should check, i don't just want to throw in an alternator is that's not the issue.  It runs fine now and i cant get it to replicate the issue.
Its a 97 2.5l, with a 5speed

Thanks in Advance NICK

[Tinkerer]

I don't know if the 1997 is the same, but I just checked my electronic copy of the 1999 TJ FSM and it says:

DESCRIPTION
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating
circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately.
If replacement is necessary, the PCM must be replaced.

OPERATION
The amount of DC current produced by the generator is controlled by EVR circuitry contained within
the PCM. This circuitry is connected in series with the generators second rotor field terminal and its
ground.

Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field.
The EVR circuitry monitors system line voltage and battery temperature (refer to Battery
Temperature Sensor for more information). It then compensates and regulates generator current
output accordingly. Also refer to Charging System Operation for additional information.

I suspect there was a bad connection and for the PCM to see 14v, it was pushing the alternator to those voltages. Once you were moving wires and the connection (perhaps ground to the firewall?) was re-made, things went back to normal.  That's a huge amount of voltage to be putting through the battery or anything else... wow!

[nickcoleman9]

Ok thanks, I will probe around and see what I can find if not PCM it is
Anyone got a good one laying around....
Thanks NICK

[FiEND]

you must have misread the voltage somehow.  i doubt any lights or electronics in the jeep would be still working if the voltage spiked that high.

the alternator creates AC voltage.  there is a circuit in the alternator that converts that to DC voltage.
the regulator turns on the alternator circuit when battery voltage drops.  the regulator turns off the alternator circuit when the battery voltage gets high enough.   it works much like the air conditioning compressor... it turns on and off when needed or not needed.

the regulator does not have any control over the amount of voltage from the alternator, only turning it on or off.  you can rule out the pcm now.

[Tinkerer]

Just like the link from an automotive instructor I included the last time I ended up discussing alternators and regulators, this one http://www.familycar.com/classroom/charging.htm also clearly states that the voltage regulator regulates voltage output and that current output is handled primarily by the resistance of the load at the regulated voltage output. (Basic application of Ohms law.)

For those who are open minded enough to continue learning and *will* read articles off-site, pay particular note to the section "The Voltage Regulator' and the later paragraph "Too Much Voltage".

Contrary to what is apparently popular opinion based on posts on here and experiences with previous co-workers, the lack of an automotive mechanic journeyman certificate does *not* mean that person is completely unable to grasp and understand mechanics, just as the lack of an electricians journeyman certificate doesn't mean that people can't grasp and do house wiring, the lack of an engineering degree doesn't mean the person can't grasp and understand material science, dynamics and building suspensions, the lack of a welding certificate doesn't mean they can't grasp and understand how to weld properly, the lack of a computer science degree doesn't mean you can't build, load, network or write software for a computer or that the lack of a class 4 license means you couldn't possibly drive a taxi cab or ambulance.

Those people may not be "certified" in the subject, but as we've all seen, some "certified" people should be "certified" in a completely different meaning coming from the mental health professions and some un-certified people do things the certified ones only wish they had done.  Heck, these automobiles we drive and work on were conceived and built before there *WERE* certifications for mechanics!  I guess they should thank the un-certified people for their livelihood, rather than "pooh-pooh" their possible knowledge.

[LLYJ]

Seems simplistic, but I had this exact scenario and the solution was replacing a semi-fried neg batt cable (albeit it wasn't obvious when I first inspected the cables housing) - another buddy had the same thing on the trail and it was just corrosion on the post s0 resurfacing the contact surfaces with a good new terminal brush solved the probem - KISS principle employed successfully in both those cases.

In both situations the dash gauge was both spiking and holding max  before and during the problem

[jpthing]

Just like the link from an automotive instructor I included the last time I ended up discussing alternators and regulators, this one http://www.familycar.com/classroom/charging.htm also clearly states that the voltage regulator regulates voltage output and that current output is handled primarily by the resistance of the load at the regulated voltage output. (Basic application of Ohms law.)

For those who are open minded enough to continue learning and *will* read articles off-site, pay particular note to the section "The Voltage Regulator' and the later paragraph "Too Much Voltage".

Contrary to what is apparently popular opinion based on posts on here and experiences with previous co-workers, the lack of an automotive mechanic journeyman certificate does *not* mean that person is completely unable to grasp and understand mechanics, just as the lack of an electricians journeyman certificate doesn't mean that people can't grasp and do house wiring, the lack of an engineering degree doesn't mean the person can't grasp and understand material science, dynamics and building suspensions, the lack of a welding certificate doesn't mean they can't grasp and understand how to weld properly, the lack of a computer science degree doesn't mean you can't build, load, network or write software for a computer or that the lack of a class 4 license means you couldn't possibly drive a taxi cab or ambulance.

Those people may not be "certified" in the subject, but as we've all seen, some "certified" people should be "certified" in a completely different meaning coming from the mental health professions and some un-certified people do things the certified ones only wish they had done.  Heck, these automobiles we drive and work on were conceived and built before there *WERE* certifications for mechanics!  I guess they should thank the un-certified people for their livelihood, rather than "pooh-pooh" their possible knowledge.

hahaha tinkerer you rule!