Replaced alternator and volts still low...

'88 XJ, 4.0, 4x4, auto, a/c, 100k

I don't use the volts gage in the cluster for voltage readings but as an indicator for when something changes. My gage has been reading left of 14, right of the red zone, and pretty much always in the same spot.

A few weeks ago the gage reading started to change. Sometimes in the red, sometimes a little higher, sometimes in the normal spot. With a DVM at the battery I was still getting 13 volts at cruise rpm and the a/c running. In another post 5-90 replied that 13 is o.k. under those conditions.

Fast forward another week and the gage is now spending a lot of time in the red. Last night on the way home from work the headlights were dim and the turn signal flasher couldn't even flash.

This morning I started to troubleshoot. The battery is a year old and has 12.2 volts static after sitting all night. After starting the engine, running at about 2,000 rpm, measured at the battery with a DVM I got less than 12 volts. Simple enough. Past experience tells me the alternator is not doing its job. Ran down to O'reilly and got a reman alternator.

The new alternator is only measuring 12.5 volts at the battery at 2,800 rpm. If I turn on the a/c and headlights I only get 11.9 volts. The cluster gage is still in the red, turn signal flasher is slow, power windows slow. I'm not getting my juice from this new alternator.

Last year I had inspected and cleaned the head to firewall ground. I did it again today. Last year I installed new heavy gage battery cables and added a cable from the negative post to the chassis. I had also replaced the small wire from the positive terminal with a heavy cable. I cleaned the battery terminals today. The belt is tight. I tightened it some more with no change.

The new alternator is putting out a little better than the old one but not by much. Maybe it's the new alternator? What else can I check? It seems to me that if you have a good battery and cables then an alternator spinning at cruise rpm and not producing significant charging voltage is defective.

Any ideas before I take it back?

thanks,
John

yup....have them test the replacement one you'll be bound to pick up this afternoon.


Sorry bout your luck.

red91inWA said:

yup....have them test the replacement one you'll be bound to pick up this afternoon.


Sorry bout your luck.

Click to expand...

X2 though I'd look a bit closer at the battery too, levels ok in it ?

Upgrade your main wiring to fatter gage. Kits cost about $89. Or check all your grounds and connections. Make sure your starter wires are not getting drenched in oil from your oil filter, check oil filter adapter o-rings for leaks, Make sure the alternator is charging correctly or take it in to a good auto electrical shop-if its a good shop they will find the problem easy. Then decline repairs if its an easy fix and DIY.

battery check too.

A couple thoughts...

Check and clean every ground you can find on the chassis! Clean the chassis spot down to bare metal (about the size of a stamp is enough,) use corrosion inhibitor, and replace the screw with stainless if it's the least bit crapped up.

You said you'd serviced the firewall ground - did you clean that down to bare metal as well? Just checking...

After you clean the grounds, note where they are. Check and clean annually, after major fording, or whenever you clean the engine bay.

Just for giggles try clipping a jumper lead onto (or very close to) the alternator case and the other end to the battery - terminal. Note any changes. There may be a "floating ground" WRT your alternator - easy enough to fix.

"Nominal" alternator outputvoltage can vary slightly - like "nominal" battery voltage - I've taken +12.6VDC as "nominal" for the battery, and add one volt for the alternator output at all levels up to maximum current output. I've seen higher on both (battery up to just shy of 14VDC, and alternators ranging up to 14.5VDC) but "nominal" is just that - what's it's theoretically supposed to be...

Nothing else I can think of right now - but I'm sure it's there (there is a huge difference for me between working on a rig, and talking about working on a rig. I invariably forget something...)

5-90

Thanks for the replies, everyone.

A 2 hour job turned into all day. I live in a rural area so a trip to the parts store is not just around the corner. Three trips today to get an alternator changed twice.

I drove the Jeep back to Oreilly's with the 1st new alternator. They tested it and said output was too low. I concur. THEY DID NOT HAVE ANY MORE ALTERNATORS.

I went across the street to Autozone and bought the 2nd new alternator. The young man at the counter wanted to test my alternator to make sure it was bad. I didn't tell him it was a new one from his competitor across the street. He said I needed a new alternator. I concur.

Brought 2nd new alternator home and installed it. 13.8 volts and all is well.

Drove back into town for the third time, got a refund from O'reillys and reclaimed my old core, gave the core to Autozone and got my $33 back, and went back home to collapse and have a beer or two.

Nothing simple is ever simple. At least I got rid of that dang splash guard under the engine. It is now in several pieces in the driveway....

until next time,
John

Except for going so damn far to the parts store, I can understand (I make it a point to live with a couple miles - walking distance, if need be - of a parts house...) I'd have to say your Jeep job came out a lot like plumbing jobs I've done - my personal best is replacing a water heater with only three additional trips to the hardware store (there are NO standards in plumbing, save gravity...)

Glad to hear you got it working. 13.x is a LOT better, isn't it?

5-90

got to love remans!

I just went through a very similar situation with my alternator (read: alternators). One thing I did while I had it apart for the second time to replace the bad "New Reman", was to add a ground wire from the neg. battery terminal to the upper mounting bolt for the alternator. It has made a huge difference in the way my electrical items work. e.g. my windows go up and down faster now, lights are brighter, etc...