Charging System Help!!

[dbcloud9]

On a charged battery the car will run for about 10-15 min. Then idle rough and eventuallly shut off the engine. When the engine shuts off, the battery is discharged. I tested my battery and alternator several times at Autozone. They ran the test 3 consecutive time and both battery and alternator checked out...Any ideas what my problem could be?

I have a 1990 240sx KA24e completely stock with 120k miles...

[let5l1de]

have you or someone else done any work to the car recently?

first check the voltage at the battery with the car running. it should be above 13v.

~m

[S14_Kouki]

OK so you charge the battery with a battery charger. Then when its fully charged you take off the charger then the battery starts to lose voltage when the car is running is this what you are saying??

First watch the battery voltage with a meter can you see the voltage drop while the car is running?? Do you have access to another alternator you can slap on there and try??

[graymaverick]

I have the same problem with my 96 240sx. I have about 150k on the meter. Car stopped on night. Figured it was an alternator problem. Got a used alternator from a 98 from a friend. Both rated at 80amps. After install problem still persisted. I went out and purchased a new battery. Still no luck. Replaced all of the fuses under the dash and engine bay. Even replaced the 75a fusable link which appeared to be melting. Car has been sitting for a couple of weeks because I am basically scared to drive it because I never know when it could cut off on me. If anyone has an idea what it could be, help would be greatly appreaciated. And I also recently did a 5 speed swap. But the car ran good for about 3 weeks before all of these problems happened.

[S14_Kouki]

Well since you have not drove the car do you think the 75a fusable link fixed the prob??

[teamsprock]

Take the battery somewhere like walmart that can test cold cranking amps. I bought a new Red top and had similar problems. I figured since it was new there was no way it was bad so I tested for parasitic drag and any other wiring problems. Finally threw an old battery in and the problem went away. Checked the battery and it had supper low CCA's. AT autozone they charge it and see if it has a charge, even a battery that is pretty much dead can test out good on their tests.

If thats not it I would have someone look closer at the alternator to make sure its not getting too hot or a diode starting to go bad.

[dbcloud9]

ARE YOU KIDDING? GRAYMAVERICK!! YOUR QUESTION SOLVED MY PROBLEM!! THANKS... after inspecting the 75a fuse, i was blown from the side of the fuse...so when you look at the top of the fuse, it looked good, but after inspecting the fuse it was blown...so let me put it back together and see what happens....I'm sure this should do...the alternator was working...but not charging my battery due to a "BAD" fuse.!!! Thanks everyone!

[dbcloud9]

Damn..240's you alway think it's more complicated than it really is.

[dbcloud9]

YUP!!! that was the problem with my CHARGING SYSTEM...PROBLEM SOLVED!

[projectRDM]

I have the same problem with my 96 240sx. I have about 150k on the meter. Car stopped on night. Figured it was an alternator problem. Got a used alternator from a 98 from a friend. Both rated at 80amps. After install problem still persisted. I went out and purchased a new battery. Still no luck. Replaced all of the fuses under the dash and engine bay. Even replaced the 75a fusable link which appeared to be melting. Car has been sitting for a couple of weeks because I am basically scared to drive it because I never know when it could cut off on me. If anyone has an idea what it could be, help would be greatly appreaciated. And I also recently did a 5 speed swap. But the car ran good for about 3 weeks before all of these problems happened.

Your problem may be harness related. It's a common occurrence on S14s that the coil wire gets grounded out to the cylinder head. Open the hood and look at the engine harness right where it leaves the fuel rail and turns to go in front of the engine, is the insulation/loom damaged or worn? Open it up and check further, if the coil wire (black/white lead) has grounded to the head you're basically shorting the ignition circuit to ground. I've fixed nearly a dozen of them now with that problem, the head has a sharp ridge right there where the harness rests, it can rub through easily. 99% of the time it blows the 75A fuse, one car I worked on blew the 100A as well. Pull the harness back, wrap it up, then ziptie it over the TPS portion of the harness, making it stay clear of the head. You may even see a few arc spots on the head where it's rubbed before.

[graymaverick]

I'm glad that me posting my problem helped someone with theirs. Thanks for the repsonses also,not to be a thread jacker just want my car back on the road. As far as the wiring harness which was mentioned, I have to get a chance to get up in the engine bay and try to see the problem. I will pm you to further discuss the problem and wat to look for.