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Discussion Starter #1
Dead battery- 98 4cyl 2wd new alternator battery starter terminals and grounds, loses power radio shuts off lights dim air bag light flashes, cluster has never worked only dash lights, truck stayed running after taking negative terminal off but wouldn't start after I shut it off, replaced all those parts 4 months ago, been fine till now
 

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First of all, you should not remove either battery cable from the battery while the engine is running on a computer-controlled vehicle, like yours; it could cause a surge that could damage the ECM or other control units. Don't assume that new or recently replaced parts are necessarily "good." Have the battery trickle-charged for at least 8-hours and then have it tested to make sure it is good. With a good battery installed in your vehicle with the cable connections clean and tight, get a voltmeter or multi-meter so you can check the charging system voltage. Static battery charge should be at least 12.2 volts. With the engine running, you can test the charging system voltage. The charging system should charge anywhere from 13.2-15.5 volts at idle and also at 3000 RPM, both with loads (headlights, heater, etc.) "on" and loads "off." If it's not within that range, there is a problem. Too high and the regulator is not working inside the alternator. Too low, and you could have a bad alternator or a circuit issue. There is a white, 10-gauge wire that runs from a fusible link near the battery (usually anywhere from 70-140 amp rating) to the "BAT" terminal at the back of the alternator. Make sure the fusible link is good, the wire is good (not burnt up or really stiff, which could indicate it has too much resistance within it) condition and there is 12v power getting to the alternator. Also, with the key "on," the charging system warning light should be illuminated. If not, check the bulb and circuit. If those all check out and the charging voltage is too low, replace the alternator. Best are genuine Nissan reman alternators; the quality of some aftermarket alternators can be a bit sketchy. If you need any more info, go to the starting and charging system section of the factory service manual (available at NICO Club's site if you need one).
 

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First of all, you should not remove either battery cable from the battery while the engine is running on a computer-controlled vehicle, like yours; it could cause a surge that could damage the ECM or other control units. Don't assume that new or recently replaced parts are necessarily "good." Have the battery trickle-charged for at least 8-hours and then have it tested to make sure it is good. With a good battery installed in your vehicle with the cable connections clean and tight, get a voltmeter or multi-meter so you can check the charging system voltage. Static battery charge should be at least 12.2 volts. With the engine running, you can test the charging system voltage. The charging system should charge anywhere from 13.2-15.5 volts at idle and also at 3000 RPM, both with loads (headlights, heater, etc.) "on" and loads "off." If it's not within that range, there is a problem. Too high and the regulator is not working inside the alternator. Too low, and you could have a bad alternator or a circuit issue. There is a white, 10-gauge wire that runs from a fusible link near the battery (usually anywhere from 70-140 amp rating) to the "BAT" terminal at the back of the alternator. Make sure the fusible link is good, the wire is good (not burnt up or really stiff, which could indicate it has too much resistance within it) condition and there is 12v power getting to the alternator. Also, with the key "on," the charging system warning light should be illuminated. If not, check the bulb and circuit. If those all check out and the charging voltage is too low, replace the alternator. Best are genuine Nissan reman alternators; the quality of some aftermarket alternators can be a bit sketchy. If you need any more info, go to the starting and charging system section of the factory service manual (available at NICO Club's site if you need one).
With the battery tested good and clean terminals it read 12.68volts running with lights on, seems to drop below 12volts when I turn on heater, slowly drops with both lights and heater on, drove an hour to work today without using any accessories and had no problem, wire going to alternator seems good also
 

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If you're only measuring 12.68 volts with the engine running, your alternator isn't working.

You should be measuring over 13 volts - typically, around 13.3 to 13.5.

Did you install a quality alternator, or a piece of crap from Auto Zone?
 

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Discussion Starter #5
Got alternator off Amazon, but I'm gonna buy 1 from autozone today because of lifetime warranty
 

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You're going to need that lifetime warranty - again, and again.
 

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Discussion Starter #7
I Know but I can't wait for a different one or afford it, my company got it for commercial price and letting me pay later, I'm hoping for the best, last 1 was oem and lasted 4 months, I wanna know what's making them go out
 

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Discussion Starter #8
Got alternator on and runs good between 14 and 15 volts, heater lowers volts below 14volts, more than my headlights, thought that was odd, front main seal is bad making pulley fling oil onto alternator, assuming that's the problem, but still not sure if heater should have such a pull on volts
 

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maybe the fan brushes are worn way down and digging in to the commutator causing the alternator to put in more resistance? but you said 4 months old so that shouldn't have been an issue unless whoever overhauled it didn't change the brushes and have the rotating parts turned. you would have to pop the end off to do an inspection to find out though
 

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here is a link with a pic of how alternators and different electric motors are set up.

Car alternators use a pair of slip rings instead of a commutator.

(Slip rings supply the rotor with constant DC current - Unlike a commutator, the polarity of the current doesn't change as the rotor spins.)

Slip rings are usually more reliable than a commutator, because they don't have any gaps between contact segments that can trap dirt and wear down the brushes.

Even so, oil splashed on the slip rings will ruin them. If you can't fix your oil leak, you might consider making some sort of splash shield to keep it out of the alternator.
 

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Car alternators use a pair of slip rings instead of a commutator.

(Slip rings supply the rotor with constant DC current - Unlike a commutator, the polarity of the current doesn't change as the rotor spins.)

Slip rings are usually more reliable than a commutator, because they don't have any gaps between contact segments that can trap dirt and wear down the brushes.

Even so, oil splashed on the slip rings will ruin them. If you can't fix your oil leak, you might consider making some sort of splash shield to keep it out of the alternator.
I don't know. When i used to work in this type of stufd it was as a mechanic for golf carts. So we would just test, break down the motors, replace brushes, get the armature turned, and put it back together. I have taken an alternator apart, here and there, but i don't know anything about slip rings.
 

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Discussion Starter #14
I replaced alternator and all problems stopped for a week till tonight I had rough idle jumping up and down like it did before alternator went out, any clue what could make them keep going bad?
 

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Are you still douching the alternator with motor oil? If so, your questions already been asked and answered. Not meaning to be harsh here, but you have to fix the other contributing factors before attempting a diagnosis.

Fusible links are junk, there's a good reason auto manufacturers don't use them anymore. I'd replace the feedline cable from the alt to the battery with one at least as heavy as the existing and maybe jump up to #8 or #6 if you have it locally available. Install a 100amp in-line fuse and watertight fuse holder and see what happens next. Also install a new heavy ground lead from the engine block or alternator mounting bracket to the battery ground. Check and tighten all other existing grounds that you can find, as well.
 

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Discussion Starter #16
I replaced front main seal from the oil leak, sorry forgot to mention that, ill try changing out cable to the alternator from battery, thank you
 
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