bradleyheathhays

96 XJ here. Everything seemed ok during a 3 hour drive then when I turn my headlights on during the last 10 min of the trip my tach drops to 0 rpm and my FM radio power cuts out, then back on. Switch my headlights off and my tach comes back on to around 7-800, idle, which is where it should be. Turn the headlights back on and tach goes out again, then when I hit the brakes (brake lights come on, I assume) my speedo drops to 0 as well. This pattern continues as I turn the headlights off and on, cutting out different gauges. Volt gauge reads just a hair above 9 but I'm not sure if this is reliable reading or if it's just pegged to the far left, not working.

This is when I notice the red 'GEN' light to the left of the instrument cluster is on. Never seen it on before but I'm assuming it stands for generator.

Stop and get out to check my headlights and they seem dim.

Course you would know all this goes down when I'm 3 hours away from my garage and tools. So I guess my next step is hopefully to get to a car part store and have the batt. and alt. tested.

Any advice on what this seems like or additional diagnostic steps? Only tools I have with me are some screwdrivers, pliers and an OBD-II code reader.

Thanks

BlueRidgeMark

Probably the alt. Getting to a parts store to have it tested is your best bet.

A new alt, a cheap set of wrenches, a few minutes in the parking lot, and you could be on your way.

BTDT.

bradleyheathhays

Thanks man. Other than alt and batt I've been told to check my ground connections but other than the batt neg. pole I'm not sure what to check.

Where should I go checking for a loose ground?

bradleyheathhays

update...

- tried to start for the first time after shutting the engine off but no go. volt gauge was around 10

- serp belt seems a little untight so laid under the front and checked that the alternator wheel was turning, and it was

- batt terminals seemed tight

- ground next to the battery on the fender wall seemed tight, no corrosion. Didn't loosen, clean, and retighten though

- was not able to find the braided cable ground on the block next to the dip stick so wasn't able to check that connection

- installed new batt from walmart and engine started but volt meter stayed at 11.5 and went down about a half volt when a/c and headlights were turned on. Ran for a while ok but shut off before batt was entirely drained.

- OBD II reader shows no codes

Next step is to get a new alternator and put er in and see what happens.

jordan96xj

11.5 would definitely appear to be low, but taking readings from gauges inside the cab can sometimes be a little less than true. Mine shows about 12.5-13.3 in the cab via ODB2 adapter and cigarette lighter adapter (that has a voltage gauge on it). With a multimeter I get 14v in the system while engine running when I test under the hood at the battery terminals.

I have a brand new alternator sitting on the bench because of a symptom just like yours. Low voltage can be due to the alternator not functioning properly, but just as likely (and I think more likely) can be that the alternator does not have the quality connections to the system (particularly ground) that it needs to get its voltage to the system while under load. I bought the alternator (for the same reasons you did), but while waiting for it to arrive, I picked up a multimeter and started learning about how to troubleshot alternators. A few tests later, I was able to determine that when supplied with proper ground, my alternator was providing the proper amount of voltage to the system. When I removed the ground (which I fashioned myself from a piece of wire with alligator clips) the system voltage would drop. I then performed voltage drop tests until I determined the near exact location that the ground was being compromised. Cleaned up that location, and problem solved. Hence, the brand new alternator sitting on my shelf for a few years (for a car I no longer own).

If you replace the alternator, there is a very good chance the problem will be resolved. However, even then, you'll never know if it was the alternator or whether the disconnecting/reconnecting just refreshed a bad connection (unless you have it bench tested and find that it is truly failed).

But I've read your other posts on this, and I know you are in a pinch to get it fixed. So I don't blame you for doing what needs to get done to fix the problem however you can. But if you can by a cheap multimeter at wally mart, it could well pay off.

madmanmarty

I would clean your grounds & battery cables,then meter it before replacing anything.

BlueRidgeMark

Yep. Unless you have disconnected and cleaned a ground, you don't know what you have.

Could be cable corrosion up inside the jacket, too. It can hide in their and make your life miserable, all the while looking like a good cable.

bradleyheathhays

Yes most def agree. Replacing the alt and getting good results either indicates the alt itself or the connections. oh well...I jumped in anyhow.

Just put a new alternator in and everything seems ok now. Messed up thing is there was a piece missing from the new alt where it attaches to the bracket and I'm gonna have to replace it AGAIN. As I'm pressed for time I guess it'll have to do for the short term.

But seeing as I'm gonna have to do this again...are there any specific alternators i should be looking into? I put the only one in listed at Oreiley's for a 96 XJ (Ultima - 90 amp) and I'm just not sure if this one is decent or not. Was in a hurry and had no time to ask or shop around.

Here it is...

http://www.oreillyauto.com/site/c/search...&vi=1180314

Maybe I should aim for one with higher amp output?

OldTires

I got mine from NAPA, can't remember which brand, but it has been good. It was a brand new model, not remanufactured, only an extra $30, well worth it.

Most replacement alts are 90 amps, but if you look at your build sheet, the original is 117 amp, which is hard to find. Haven't had an issue with 90 amps though.

Glad you got it replaced.