Volt-meter alternator diagnosis. HELP!

[sheadee240]

The other day my car died, and if I let it sit for a half hour it will start again. But after driving for 5 minutes the air bag light will flash followed by the car loosing lights and then loosing spark (dying). I think the battery is fine and the alternator is F$cked!

How do I test my alternator with a volt meter?

I'v done it before on a motorcycle, but i forget how.

I've heard that, you just start the car and disconnect the negative terminal (obviously without a volt meter), but that sounds a little fishy with new computer controlled cars.

I have 1997 240sx, that crapped out on me and Im pretty sure its the alternator, but I need to test it.

Thanks

[Mayhem_J30]

the car should run on it's own w/o the battery after being started, but it can't run with it so your alt is definately screwed. your weird electrical symptoms are big signs that it's an alt. i do this, don't even have to d/c the battery. just put the meter on the battery. make note of Voltage. have someone start car, make note of voltage drop. then test it while car is running. If alt is bad you'll see the voltage fading on the battery as it's drawing power from it rather then the generator. Interesting the battery still has juice to start it after it dies.

[APEXi240]

I had an 85zxt that had the exact same symptoms...It's the alternator.

Depends on how new the battery is...plus I think Nissan puts in some decent batteries from the factory (still have my first one in my 240 100k, my sentra had 130k on it before the battery died). So depending on how new the battery is it'll start again, a couple of times anway.

Ok, not to jack the thread but I have an alternator question also. When your alternator gets wet your car will not start correct? This happened to me the other day (it rained all night, and the next day). I did not use the car for almost 24 hours, and I assume the alternator got wet, because it wouldn't start...Is there any way to prevent this from happening again? This was the first time it happened, and I'm a little nervous that I'll be out a car every time we get percipitation.

[erich]

To see if your alternator is working set the voltmeter to measure voltage (duh!) and look at the battery voltage while the car is running. A fully charged car battery has about 13.2 volts with no load. The charging voltage should be 14 or so volts. If it is less than 13 volts then no charging is going on. Try raising the RPMs to over 2K and measure again. I have seen weak voltage regulators that needed to be revved a little before they kick in. If this helps then the voltage regulator needs to be replaced. I am not sure if the VR is internal to the alternator or not on the 240. Maybe someone else knows where the VR is.

erich

[sheadee240]

How do I test amps?

To see if your alternator is working set the voltmeter to measure voltage (duh!) and look at the battery voltage while the car is running. A fully charged car battery has about 13.2 volts with no load. The charging voltage should be 14 or so volts. If it is less than 13 volts then no charging is going on. Try raising the RPMs to over 2K and measure again. I have seen weak voltage regulators that needed to be revved a little before they kick in. If this helps then the voltage regulator needs to be replaced. I am not sure if the VR is internal to the alternator or not on the 240. Maybe someone else knows where the VR is.

erich

[matt240det]

doesn't autozone or something do free charging systems tests? just a thought.

[johnsharpe]

How do I test amps?

To test the current capacity of a battery you need to put the battery under a severe load, among other tests...I don't think you can do that in your carport. Take it in to a shop to get the charging system tested. I di that last weekend and it cost me cdn$20. Well worth the peace-of-mind, IMHO.

John

[sheadee240]

To test the current capacity of a battery you need to put the battery under a severe load, among other tests...I don't think you can do that in your carport. Take it in to a shop to get the charging system tested. I di that last weekend and it cost me cdn$20. Well worth the peace-of-mind, IMHO.

John

I don't think you are right about this. I have tested the output in amps of my motorcycle's alternator with a voltmeter and a little regulator bypass action. There must be a way to test the alt output on the 240 with a volt-meter. And you shouldn't have to create a severe load, just need to rev the engine.

[sheadee240]

john and shea are talking about two different things. The average home mechanic doesn't have the capacity to load test a battery. Testing the alernator output can be done with a voltmeter.

shea, it's probably your alternator. Is the belt tight?

Yeah, I certainly hope it is the ALTERNATOR, I just dropped $250 @ http://www.nissanparts.cc for next day shipping of a new factory alt.

Thanks

Just out of curiousity how do i test amps with a volt-meter on my car?

Thanks

[sheadee240]

Do you have a link for all oem?

[sheadee240]

Thanks for the info.

FYI.. that is a rebuild, and the factory unit hopefully justifies the extra $bean$

[Thor]

$250 for an alternator?! Granted it's new but there really isn't much difference in a remanufactured one.

Personally, I only buy alternators from O'Reilly's or the like. If one should go bad after a year or two it is free to replace...one time cost, no worries.

Does the new one from nissanparts come with a lifetime warrantee? If so, you will still have down-time if you have to mail it back.

My 2 cents.

[sheadee240]

$250 for an alternator?! Granted it's new but there really isn't much difference in a remanufactured one.

Personally, I only buy alternators from O'Reilly's or the like. If one should go bad after a year or two it is free to replace...one time cost, no worries.

Does the new one from nissanparts come with a lifetime warrantee? If so, you will still have down-time if you have to mail it back.

My 2 cents.

I did some searching on either here or 240.org and one guy that was a mechanic said that his shop had tried every major brand of rebuilds, and after loosing there shirt on extra labor on replacements they stopped doing remanuftured joints all together. A mechanic friend of mine also told me if it was him just use the OEM, so you can drive 4 more years with no worries instead of getting 6 to 18 months out of a rebuild. Even if it's under warrantee, it not worth the hassle to keep replacing.

[scruf1986]

The same thing happened on my car a couple of weeks ago. I was able to race mine (for fear of my battery dying) to Auto Zone and get it tested for free. Thats the best way. But all you have to do is just hook up the voltage meter and see if the voltage falls. If not, turn on your AC and radio and role your windows up and down because that puts a lot of strain on the battery and the alternator. Have fun

[Stock-S13]

Hey thats what i did today as well and sure enough the guy told me it was using the battery and i should get home before it got dark but yeah iam in need of a new alternator i saw import have it for 138. ill check oem as well ow yeah mine was covered with oil whats that about??