97 TJ PCM/Voltage regulator problem

[harry61]

My first post here, so I'll apologize for any institutional faux pas's and the length of this before I commit any.

History: I recently bought off Ebay a 97 TJ SE 4cyl, 5 spd, AC, soft top, with 32's, 94K. My wife wanted it, so she got it. The prev owner owned it for 9 months, and described it as being in excellent condition. He was selling it because of personal reasons. He said that the only problem with the jeep was it stalled occasionally, and his Firestone mechanic diagosed the problem as needing a new fuel filter, which would cost less than $250 to replace.

Sure, I thought. So, I drove half way, gave the man his money, and hooked the uhaul trailer to my rig and drove home. That was in January. Since then, I've replaced the steering gear box (seal gone) fan clutch (locked solid) water pump (bearing gone from locked fan clutch) CPS (wires melted due to being routed incorrectly) Recored the radiator, new hoses, removed and rebushed the fuel injectors, replaced both motor mounts, cleaned the FI system and the 3 sensors attached to the plenum, new serp belt, retracked the wiring system to chase gremlins, brakes, tie rod ends, cleaned about 300 lbs of mud from the underside, etc...... I've put quite a bit of time into this project already. The fuel system pressure was at 48psi, so there was no prob with the filter. I had an irritating, intermittant stalling condition, in which Sybil would lose power, the engine would stall, and then not restart. Switching the key on/off to give me error codes was not helpful, as no codes were displayed. MY OBDII computer also would not pick up this problem. The only codes displayed were P1594 "charging system voltage too high".

This loss of power and stalling was a potentially dangerous condition, as it occurred not only on the loop about town, but also in the city. After much head shaking and wringing of hands, I tracked it to the coil plug minutely working its' way out of the coil when hot. The snap that hold the plug into the coil was broken off by a previous owner/mechanic. A zip tie now holds it in place, and the intermittant stalling problem is resolved.

My main problem now is the "charging system voltage too high". This came to my attention as I was driving down the loop at 55-60mph and the volt meter went from 14v to in the red at 19v. I was concerned, and pulled over, allowing the jeep to idle and 7 to 10 seconds later, the needle returned to 14v. I have since measured the output of the voltage system with 3 seperate mediums: A hand held tester which measured my system output at 13.6 volts (constant), a snap on portable shop system tester which measured my system output (constant) at 12.6 volts (2-4 amps), and the obdII portable computer which measured my system (fluctuating) at 13.6 to 15.1 volts. I took the jeep for a 15 mile test drive with the OBDII handhelp computer hooked up and did a complete diagnostic run on it. The charging system fluctuated wildly between 13.6 and 15.4 volts, changing as rapidly as the computer would update. (RPM, MPH, and all other parameters were constant). During this test, the volt meter once again pegged, into the red, at 19 volts, but the voltage according to the OBDII handheld did not rise above 15.4. Which leads me to believe that my dashboard Volt gauge is suspect.

The point of this long missive is that the TJ's (according to my Alldata system) voltage regulator is contained in the PCM, and not the alternator. This is my first TJ (I've owned a 94 YJ, 2 XJ's (99 and 88), 3 CJ's (all 77-78's), a 72 commando, and a 44 MB) and I am unfamiliar with this system. I have already purged the PCM following instructions I found on this site (remove neg cable, ground 30 secs, key on, headlight on/off, key off IIRC) but the charging system prob still exists. Last night I went for a short night time run and with the headlights on (under load) the voltage gauge stayed steady at 14v (I didn't have the OBDII hooked up).

Does anyone have any advice for me? Unless there is a method for me to repair this, it looks like I'll have to buy a new PCM from the dealer.

Thanks for your help and advice, and sorry about the length of this problem.

Harry in San Angelo, TX

[de6w6it]

If it came down to it, I would try and find a pcm from a junkyard or on ebay or something, before the dealership took mr for all I am worth.
I was under the impression that the coil and voltmeter are all one piece. My brother was telling me about getting this aftermarket coil, and how you have to deal with the fact that the regulator is part of it or something, you may want to look into that.
Though, I would also agree that your in dash voltmeter may be the problem, if all your other methods of testing the voltage is saying it is within normal parameters. Does the check engine light come on when the vm is pegged at 19?

[Jerry Bransford]

Yes the alternator's voltage regulator is contained in the main engine computer. However, it's a normally very reliable component and I wouldn't jump at it being the true root cause of what's happening. I'd take all the battery cables off, thoroughly clean then examine them for corrosion inside the connector is connected to the cable, then remount and tighten them.

Make sure to do the same thing to all the ground cables that connect the engine and battery to the chassis and tub.

Do the simple stuff like the above first, I wouldn't worry about the voltage regulator yet.

[de6w6it]

, sorry, guess I was wrong about the regulator being in the coil. but def check all the connections for corrosion and such, that could definitely do it. Make sure there is not break in the cables you cant see because it is in the insulation either.
I would keep another voltmeter hooked up, keep an eye on that, and see what happens when it gets pegged, look at second voltmeter, cars voltmeter, and check engine light and code.

[Mudinyeri]

You have a loose ground somewhere. I had exactly the same symptoms on my '04 and it came down to a ground stud nut that had worked itself loose. Check every ground in the wiring sytem before you go to the expense of buying a new computer.

[KaiserJeep]

I concur that a loose ground behind the dash could be responsible. Taking off the dash to get to these is a pain, but just follow the directions in the manual.

One thing to check first (just becaus it is MUCH EASIER), is the two-conductor wire harness that plugs into the alternator, connecting it to the PCM. This is the voltage regulator connection itself.

[harry61]

Thanks for all your advice. I shall get on it pronto. The Jeep is running very well presently. The volt meter still pegs occasionally, but I'm ignoring it for now. At night, with the headlights on, it functions normally.

I shall go and clean and refurb ish or replace as necessary the battery cables, and I shall also become acquainted with the alternator and connections. I will also check all ground wires.

Would you be so kind as to tell me where the ground wires are located? I have found two already, one in the vicinity of the firewall and the back of the engine, and another in the vic of the pax side motor mount.

Thanks again for all your assistance,

Harry
San Angelo TX