Need Advice

'92 Jeep XJ 4.0 HO. 90 amp alternator. Check engine light came on, flashed a 12 and a 41 code. Tested battery, showed good at 12.79. Done this Mod. to it..http://www.olypen.com/craigh/charge.htm Now it just flashes the 12 code (Battery Disconnected blah blah after 50 something) Sorry can't remember all the wording. Dash voltmeter shows around 14, when i turn on everything in the Jeep, it goes down to around 9, even the RPM needle is bouncing. Then i take the ground off of the battery post, Jeep ran for 10 minutes, engine didn't quit. Do i need an alternator, battery or both. or do i have a bad ground?

I have a 100amp fuse between the alternator and power distribution center. If i get a 136 amp alternator will i need a larger fuse in place of the 100amp one? Please help.

MEMBER #579

Nobody knows? Just some ideas.

Member #579

what do you mean by "everything on"? Do you have a lot of aftermarket electrical stuff? The stock alt should be able to power everything that you have stock.

I can't tell you the exact problem that you have, but I had the same one in my old (RIP) 89, I did the Craig upgrade to the wires, and I even got a 130amp (or something close to that) alternator, and when I turned everything on (everything stock, hella's, 4 KC's, reverse lights, and AC) I dropped to 9-10V, it wasn't pretty. I eventually just delt with it, I could never make it go away. I added a bunch of ground wires too. I did upgrade my fuse to a 150amp I believe.

I think I had a constant power drain, or something shorted out, I toiled with it for a while, and I even put a new stock alt in (this did help) but I kept the underdrive pulley from the HO alternator that I bought from AlterStart (ebay seller). I think my HO alt was messed up. With the stock alt, ground straps, and wiring upgrade, I managed to stay at around 11 at idle with everything on, it would only get to 13-14ish if I was over 2K RPM's, which I suppose isn't horrible.

You can always take the alt out and get it tested, give you an idea of exactly how many amps it is pushing at idle.

The Jeep died before I could fully fix it. Sorry to not offer a solution, but your not alone here.

Todd

After the Craig upgrade, was your lights any brighter? The only aftermarket stuff i have right now is Hella 500's on the front bumper. Before the upgrade, i was getting the error code 41 also. But now the 41 code is gone. Maybe the battery is going bad. It's a Wal-Mart special. About 4 years old. Thanks for the reply.

I was refering to my normal stuff, like A/C, flashers, lights etc.

Then you should have your alt checked out, the battery could be bad as well, you can check that yourself with a battery fluid tester. If your just running some hella's you should not be down that low. The craig upgrade made my hella's brighter, not my headlights, I think I had something else wrong with that though. Like I said it died before I could figure it out. I'd just take the alt out and get it tested. Did you measure the voltage at idle and then also at higher RPM's and see when it kicked into 14 volts?

Todd

NHxj4x4 said:

Then you should have your alt checked out, the battery could be bad as well, you can check that yourself with a battery fluid tester. If your just running some hella's you should not be down that low. The craig upgrade made my hella's brighter, not my headlights, I think I had something else wrong with that though. Like I said it died before I could figure it out. I'd just take the alt out and get it tested. Did you measure the voltage at idle and then also at higher RPM's and see when it kicked into 14 volts?

Todd

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At low idle it stayed around 9 volts, at high idle, it would go to 14 volts for a short time, then to 9 volts. Just moved up and down in high idle. I took the negative battery cable off for about 10 min. the motor never quit.

Member #579

fire325 said:

At low idle it stayed around 9 volts, at high idle, it would go to 14 volts for a short time, then to 9 volts. Just moved up and down in high idle. I took the negative battery cable off for about 10 min. the motor never quit.

Member #579

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Cartainly sounds like your alt, I believe that you have an external voltage regulator on that (I do on my 93) so that could have something to do with it as well. If your jumping voltage, either could be messed up. I believe that you can test the actual voltage of the alt by bypassing the voltage regulator. You would need to hook up aligator clips to the alt, but not the voltage reg, that would give you the true voltage that the alt is putting out. Try that, and if the voltage still jumps, get a new alt, if not, get a new volt reg. I'm not sure which wires you would need to hook up to, I'm also not sure if your volt reg is external. If you look at the connection on the alt, do you have just 1 nut and then a harness, or do you have 1 nut (wire to battery) and a little black box that is attached via 2 very small nuts? If the 1st, your voltage reg is internal, if the latter, it's external.

Todd

Got a new battery today, installed it, same thing. Must be alt.

I guess i have the external voltage regulator. There is a small rubber looking box, with maybe an 8 guage looking wire going into it.

Can i just replace the voltage regulator instead of the alternator? I can get a used one at the scrap yard for $40.00. Thanks for the help.

Member #579

Alternator was bad. Voltage regulator in my '92 is in the ECU. Alternator repair dude said, upgrading battery cables(to larger size), bypassing the PDC using a fuse or breaker is a very good modification.

So, the modification is done, had to order an alternator. My old one was beyond repair. It was cheaper to buy one (remanufactured) $112.00 to rebuild. $98.00 for remanufactured included shipping. Thanks for the help. Maybe this will help someone else later.

Member #579