I want to see if my alternator has taken a dump on me. Is it safe to pull the negative cable off the battery while the engine is running, to see if the alternator tries to charge. I know that was the quick way to check alternators on the good ol' cars (pre-ECU,EFI) of the past. Do I risk frying anything by pulling the negative while the car is running?

91 Maxima SE

 

go for it. just be sure to have dry hands when you do it. shouldn't hurt anything..

BUT.. it will be safer and more accurate if you just take the car to a parts store and have them test it. their machines can tell you if you've got a bad alternator, battery, voltage regulator, etc etc.

 

Why go to all that trouble? just take a multimeter and put it on the battary posts with the motor running. A good altenator should be about 14V or more. If it is completely bad it will read 12-12.5 volts or lower.

 

Good suggestion. I knocked the dust off my voltmeter and test light and checked things out this morning after charging the battery overnite. Using the test lamp, (probing pos. post and negative cable and engine off) I checked for a system short while the positive cable was hooked up and negative cable off. No light = No shorts..GOOD. I hooked the voltmeter post to post and it read 12V. The first time I started the car it jumped to 14V (scratching my head at this point). The second time I started the car it jumped to 14V then suddenly plunged to 12V then 11V. I'll be pulling and replacing the alternator today. Just thought I'd update y'all. Thanks for the suggestions!

 

that's usually correct, but you can't always go by that.. nissan alternators tend to run a little low on voltage anyway. at idle, I've seen them run at 12.3-12.6 volts. get them above 1200rpm and they're over 13V. only time I've seen over 13.8V on any maxima I've worked on (probably over a dozen now) is when the RPM are over 3000.

 

That pretty much is exactly what was said on the documentation I received with the new (rebuilt) alternator. It also stated that there have been several service bullitens produced by Nissan in regards to poor charging Maximas. There are smaller pulleys available to help correct some under charging alternators in Max's.