Alternator down to 2 phase?

Last night after getting gas, I went to start up my 96 XJ (Up-Country) and the guages sort of faded out and she had no juice left. So I got a jump, but it wouldnt stay running unless I kept the rpm's up - if I let off the gas it would just sputter out.

So I drove it home that way with the GEN light on the whole way and the headlights flickering. Ran pretty rough but got me home. Pulling into my garage, I let my foot off the gas and it stayed running at idle but sounded like crap.

Im figuring that I lost one of the 3 circuits in my alternator. My battery is dead, I think due to the engine using battery power to compensate for the low alt output.

Called dealer, $290 for an alternator with only a 1 year warranty. Ugh. Parts store has some for around $120-$160 (rebuilt) with a lifetime warranty. With the Up-Country package, I read somewhere that it has a "heavy duty" alternator, but I dont see anything like that on the parts pages.

Im pretty sure this indicates a failed Alt, I think I should just pull it out and get a new one. Anyone have any other ideas? If the cables were toast would I have even been able to run? Can an alternator lose one phase and still limp along, or is it more of a works or its dead situation?

- Brian

When you say that the battery is dead, do you mean you had it tested and its fried?

I have been stuck in the woods twice before because of electrical failure, once because of the alt. and once because of the battery. Both times the symptoms were exactly the same, both times the jeep was running and moving, first loosing all power accessories and then engine spark.

Have you tired just replacing the battery yet? when i got stranded the second time, i thought it was because the alt. went out again, so i went to K-mart and picked up an el-cheepo that i could run the engine off of long enough to get off the trail. I put the k-mart battery in, fired it up and prayed it would last long enough. I am still using that battery today. The alternator had no problem, the battery just crapped out.

dont go dealer on a replacement alternator, for roughly the same price you could put in a powermaster or a mean green, Much more output. If not you can get one from the local part store with higher than stock output. When changing, it also makes sense to upgrade the size of your wires.

I havent had the alt or battery tested yet. I just meant its dead as in there is no power in it currently, other than a small surface charge. It might be ok after some charging.

I've had the battery go before, but it never gave me the GEN light or ran rough once it was jumpstarted.

Zoner said:

I havent had the alt or battery tested yet. I just meant its dead as in there is no power in it currently, other than a small surface charge. It might be ok after some charging.

I've had the battery go before, but it never gave me the GEN light or ran rough once it was jumpstarted.

Click to expand...

It can run rough however. The minimum amount of volts for an FI engine to run on is, I thnk 9. so if your dipping below that...it could cause problems.

if the gen light is on, the alt is toast. It can and will kill the battery if you continue to drive it.

There is a component called a rectifier bridge that converts the AC to DC voltage. When this fails, AC voltage is introuced into the battery. needless to say, batteries don't like AC voltage.

Remember to charge your battery before you start the engine with the new alt. Alternators nowadays are not able to withstand charging up a dead battery and will reduce its overall lifespan.

Typically, low charging is an indication, one of the diodes is toast. Usually/often charges around 9-11 volts. depending on the regulator (it´s gonna try and compensate).
If you´ve driven through any mud or dirty water lately, might try washing the brushes and slip rings out with hot water. Dirt under the brushes, messes with the output.
Only way to know, if it´s the alternator or the battery, is a bench test for the alternator and a load test for the battery. Everything else is guesswork.
Possibilities are are a bad diode, regulator, brushes/slipring, wiring, contact/corrosion or even a dead/shorted cell in a battery.

Since you have a Mitsubishi alternator (91-up XJ, 90-earlier had Delco) you shouldn't have any trouble finding a replacement that won't kill you. You do have a few routes to go...

Let's see, you've already been to the dealer and the local parts house, but you've also got some of the online outfits that do underhood welders (www.powerman.com and www.mobiweld.com spring to mind) as well as finding a D-I-Y kit. Generally, alternator failure can be traced to worn brushes or popped rectifier diodes, and both can be replaced fairly easily. Heaven knows how many I had torn apart on the bench when I was wasting time as a parts guy... As long as you don't need to replace the armature, you're gonig to get away cheaply.

Of course, you'll notice I didn't say anything about a voltage regulator. Reason for that is the Mits unit you have is externally regulated, and I don't recall if it's a standalone frammis or built into something, and I don't want to subject you to Bogon emissions... Besides, most alternator failures go back to what I mentioned - brushes or rectifier diodes.

Time well spent would be to go to the library and look up mid- to late-70's repair manuals, as they will give you troubleshooting and diagnosis information on alternators. The most complex tool you need for basic troubleshooting is a decent DVM, which you should have anyhow.

Why do I suggest all this? Imagine losing your alternator outside easy range of a parts house... Spare parts for rebuilds are smaller and easier to carry! Even if you don't need to do this regularly, you should know how (just in case...)

5-90

If you are looking to upgrade the alt, the following info had been previously posted to upgrade to a 136amp alt. It is an easy swap as they are the same bodies.

OEM 90 amp alternator(OEM PN:56005685AB

OEM 136 amp alternator(OEM PN:56027913

136amp Found on:

1997-1998 Dodge Dakota
1998 Dodge Durango
1997-1998 Jeep Grand Cherokee
1997-1998 Dodge Ram Pickup
1997-1998 Dodge B.Series Van

Or a good shop can wedge about 200A into that case. No worries - the system will only generate and take what it wants (if you're just running your engine, that's about 15-20A. If you're recovering from a flat battery, that's all of it!)

F'r instance, I've got a Delco in my 88 that gives me about 160A at max output, and one in my wife's 89 that's good for about 150A. Need the address of the shop I use?

5-90

Well, I guess to start I should take the battery down and have it tested. Then the next step is going to be checking the alt, I'll probably look into that 135A upgrade.

I'm a little far away from CA, so I'll look around over here - but thanks.

For the '88, AutoZone offered two choices with limited lifetime warranties, and two rebuilts with 1 year warranties. The cheaper lifetime unit is a rebuilt, and the more expensive (still about half of dealer price) is all new. That's what I went with.

Be sure to pay attention to the advice to recharge the battery before putting a new alternator on line. Trying to kick start a dead battery will fry an alternator.

I took the battery down and had it tested, they immediately said it was fried. It was just under 2 years old, so I got a prorated replacement for $20. After replacing it, everything seems fine now. I havent dug out my DVM to get a second opinion on the charging voltage, but the in dash gauge is showing a hair under 14 so I'm going to go with it for now.

:dunno:

I guess the battery plays a big part in the loop. Having it fried could have made it behave like the battery cables were not connected (open loop) or perhaps the voltage regulator was trying to divert all the juice to charging the battery leaving it too low to keep the engine happy at low rpm.

just goes to show, you need to investigate all posible causes/failures before you start throwing parts/money at a problem.

glad you got it taken care of, and for alot less than a new alternator would have set you back :cheers: