Alternator on it's way out or ?

[goody90q45]

My 90Q with 115k miles that's been my daily driver for the past couple of months has what I think is a bad alternator. Since this is my first experience with charging system issues I wanted to run the symptoms by the pros before I jack the car up and replace it.

For the past couple of days at standing idle (750 rpm) and below 1000 rpm when slowing, the antilock and brake lights are illuminated along with the "Battery Charge Low" warning on the odometer display. When the car is moving above 1000 rpm only the brake light stays on (but dimly) and the antilock light and battery warning message both go away.

I've measured the charging voltage using Nissan Data Scan (and backed up the readings with a voltmeter) quite a bit over the past few months while saving this Q from the undertaker and its always read 14.3v with the engine running and 12.3v with the engine off. It's now reading 11.8v charging and 11.6v with the engine off.

I'm pretty sure I have a bad alternator and not a bad battery but wanted some agreement with my diagnosis and encouragement before I drag my old @ss under the car.

[3Q Jay]

get to it!

much easier (essential?) with the tension rod and bracket removed.there is one bolt on back top of a/c compressor that is a pain.i lockwired the thrubolt nut onto the back flange cause i couldn't get my fingers in there. others have used tape, etc.

amp should be there saturday.

[Dabizzo1]

Assuming it is the original alternator, i'd replace it just due to age. Unless the abs motor is humming(relay), I'd assume the diode packs inside the alternator cannot keep up. Decade-plus HEAT is the killer. Cyclic heat. Combined with the fact that our alternators are bottom mount, gunk inside the windings act as an insulator to worsen things ventilation-wise due to road grime (mine was filthy even with the belly plate on). Dim display lights to me are a sign of a charging system that cannot keep up for a hidden reason. My brand spanking new oem replacement cured my premature battery dying woes. Check your cables first as a fine toothed comb inspection...it was a culprit in my case as well. This is the first car I've ever seen with corrosion on the negative cable frame mount point with cracked cable windings to boot(it was a Dallas commuter car before I got it...HOT). Check the peripheral connections first for continuity...could buy you some time on a replacement. Boris

[goody90q45]

I started pulling parts on Sunday morning to change out the alternator and thermostat. When I got under the car to remove the belts I noticed that the alternator belt was very loose with about an inch of deflection and the alternator idler pulley was noisy. I'm pretty sure the loose belt was from me checking the pulleys a few weeks ago and not tightening it up properly.

I decided to change the alternator out anyway but stopped after getting the AC compressor upper rear bolt 2/3 of the way out and deciding that I would never be able to get my paws up there to reinstall the bolt. The other 3 bolts looked pretty straightforward but I didn't want to get in over my head and was going to take it to the shop for the alternator install.

I put everything back together and installed a new thermostat while the battery was on the charger. After 6 hours the battery was not quite ready but at about an 80% charge so I installed it and still had the three warning lights for a bad alternator. This morning I started it up again and after a couple of minutes the "low battery charge" warning went away and all has been well since. I'm thinking that the battery was not fully charged and it took about 30 minutes of the engine running for the alternator to recharge it.

I'll give it a couple of days to make sure that it's not an intemittent failure but it looks like the loose belt and maybe the idler pulley were the culprits.

[Q451990]

Here's to hoping it was a simple belt adjustment!



Heath

[elwesso]

Before going any further, id definitely try going to autozone and getting a free test. They have really nice equipment to test alternators!

[goody90q45]

Here's to hoping it was a simple belt adjustment! Heath

So far so good. It's been 4 days and none of the warning lights have come on so I can blame it on the loose belt. Now I've got to deal with another dead injector (or two).