Weak alternator 97 Maxima?

[zorobabel]

I've never had to deal with a faulty alternator before, so I'm hoping for some advice here.
The car is a 97 Nissan Maxima auto, CA spec. No warning dash lights (or codes - last time I checked).
I had my suspicions about something not being right, and the car has been like this for about a year.
The first symptom I noticed was whining correlated to engine rpm when there was an electrical load.
I also noticed the lights dimming and blower motor reduced output/speed at low engine rpm. Idle engine rpm in P or N is 700 rpm, but drops to about 550 in gear.
About six months ago I noticed the following: after idling in gear for a while at say a traffic light, the engine rpm would start going up to 800 rpm.
I got the idea at this point that the ECU/ECM is trying to keep the voltage stable by increasing engine rpm.
I did some measuring with a multimeter rigged to the cigarette lighter socket, got some readings, and for the convenience factor I ordered a cigarette lighter socket usb adapter with voltage display.
I monitored voltage for some time and this is what I observed:
-After starting the car, any kind of higher rpm would send voltage to 14-14.3
-Regular driving (1500 rpm to 3000 rpm) voltage is about 13.5-14
-Idle in neutral voltage is 13 or higher
-Idle in gear (550 rpm) with no electrical load voltage is 12.7 to 13
-Idle in gear (550 rpm) with electrical load and the voltage starts slowly dropping from 12.7 to 12-12.1, at which point the ECU/ECM starts raising rpm and the voltage goes to 13 or higher.

The car has no driveability problems yet, and the battery is 17 months old (Everstart Plus I believe, the one bellow the Maxx). I am also running the 24F size battery.
Changing the alternator in this car is not a breeze.
I also had 2 white smoke events about 6 months apart about 2 years ago; the smoke was from the front of the engine, where AC, alternator, serpentine belt and pulley are. I have changed the AC pulley bearing as it was noisy about 6 months ago.
A year ago, I had the alternator removed from the car while working on fixing leaks.
Please share your thoughts.

 

[SOHCman]

Being a 97 it may have a manually set "base idle" that could be adjusted up. I don't think any vehicle ever should be idling as low as 550. 750 maybe in gear or not.

 

[zorobabel]

Originally Posted By: SOHCman
Being a 97 it may have a manually set "base idle" that could be adjusted up. I don't think any vehicle ever should be idling as low as 550. 750 maybe in gear or not.

Thanks for replying! The car was the same way when I bought it, 4 years and 60k miles ago.
AFAIK, the manual only talks about setting the idle in neutral. I have cleaned the IACV valve, TB, replaced the TPS and adjusted TPS and idle per manual and TSBs (rather time consuming).

FWIW, my wife's Corolla is at 13.7-14 V at all times.

 

[JamesBond]

Maybe try cleaning the throttle body and idle control valve.

 

[eljefino]

Your readings alone don't sound too awful. An auto parts store with Midtronics tester can give you a free on-car test that also detects alternator ripple if you lost a diode.

 

[benjy]

a free "load test" at auto zone or your friendly local garage will tell you if your charging correctly or NOT!!!!

 

[macarose]

This generation of Maxima is incredibly sensitive towards having a factory OEM alternator. Aftermarket ones are usually substandard.

I had to deal with this just a few months ago. Your best bet is to make sure the alternator is an original (I bought a junkyard one for $35 and returned the one I bought on Ebay) and related to this, replace the wire harness assembly that plugs into the alternator on top.

Do this and all your problems should be solved.

All the best!

Steven Lang

 

[zorobabel]

Thanks for the replies, I'll try to hit a chain parts store today.

 

[zorobabel]

Thanks for replying!
I seem to remember I have a Hitachi alternator, but I took no photos to double check.
There is a Bosch aftermarket alternator for this car, what do you think of it? Junkyards are a racket around here.
I will look into replacing that harness.
Did you remove/install the alternator from the bottom or the top?
Originally Posted By: macarose
This generation of Maxima is incredibly sensitive towards having a factory OEM alternator. Aftermarket ones are usually substandard.

I had to deal with this just a few months ago. Your best bet is to make sure the alternator is an original (I bought a junkyard one for $35 and returned the one I bought on Ebay) and related to this, replace the wire harness assembly that plugs into the alternator on top.

Do this and all your problems should be solved.

All the best!

Steven Lang

 

[zorobabel]

Took the car to O'Reilly, an employee hooked it up to a device (not Midtronics) and he got that the diodes are bad. He said that the corroded positive cable could also cause his device to give out such a reading. He seemed to know his business (he praised the reflectix insulator I made for the battery )

I forgot to mention that the positive battery terminal corroded away and fell apart about 2 years ago (I had to rig a replacement terminal in the office parking lot) and the corrosion goes under the insulation of the cable. The previous Costco battery leaked at the positive terminal. The resistance between the alternator positive bolt and positive terminal is about 1.3-1.5 ohms with my cheap multimeter.
The resting battery voltage is 12.5V.

 

[SHOZ]

As far as manually setting low idle speed here's how i did it on a '97 Ford Taurus.

You need a OBDII data reader so you can monitor rpm and engine temp. Or you can wing it by ear.

Make sure the engine is up to temp and idling. First disconnect the IAC power and it should die. If it does then reconnect the IAC and start the motor again and then turn up the idle speed with the throttle screw. Then Disconnect the IAC and turn the idle speed out until the engine is idling around 400 rpm with no IAC.

Then disconnect the battery to clear the learned behavior of the ECU. Restart car and let idle in park or neutral for a few seconds, turn on all the electrical and wait another few seconds, put in gear with an auto and let it idle with all electrical loads for a few seconds.

This will give the IAC more 'electrical headroom' to work with and a finer control.

As far as the voltage readings you get that is quite similar to what both my Hyundais get under the same circumstances. I would say i do see the voltage drop some in summer with the heat.

 

[zorobabel]

Thanks, it was a similar procedure setting the idle speed - resetting the memory, but as I remember the TPS had to be disconnected on mine not the IACV, and the idle adjusted from a screw on the IACV, the TB idle screw was not to be touched (had a paint mark on it).

I was reading that a method for determining if the alternator diodes are bad is to check for AC voltage at the battery. The Maxima has 28V AC at idle, so I almost freaked out. Then proceeded to test 2 more cars: the Corolla has 30V AC at idle, while a neighbours F150 has 30V AC at idle. The last 2 also have 27V AC with the engine turned off (I haven't checked the Maxima yet).

 

[ctechbob]

There shouldn't be ANY AC with the engine off at all. I think you might need to try another meter.

 

[zorobabel]

So on the Maxima with engine off I get 27V AC with the above cheap multimeter and 29V AC with a Micronta multimeter.

 

[zorobabel]

I replaced the alternator with a junk yard unit, no marking or labels no Nissan logo on the back. I removed 3 alternators at the JY, one had a wobbly pulley, another conducted electricity both ways (probably bad diodes), and another one I picked up (from a 98 I30). I took a gamble, since those crooks at LKQ want extra for 30 day replacement, but it tested out good on the bench at a parts store.

It turned out to be longer than the one on my car, so I had to remove the washers from the mounting bolt (I should have taken the I30 mounting bolt, probably longer). But I get 14.4-14.5V after starting - while recharging the battery and 14.1-14.2V after that, at all rpms.

Thank you all for the replies!