Interesting charging system foible, any thoughts.

[IanS]

Ever since I pulled my 240SX out of storage Ive been having a weird issue with my charging system.

1995 240SXRedtop SR20DETStock SR alternatorMiata battery

Its been a month since the car came out of storage. With the ignition on, engine off, my volt gauge reads 12 volts. If I start the car, the volt gauge will read between 11 and 12 volts. If I just let the car idle, it will run until the battery can no longer support the engine, the battery light will come on, and the engine will stall.

Sounds like a dead alternator right? Well, if I start the engine, wait for the oil pressure to stabilize, then rev the engine to around 2300 rpm, the interior lights will brighten, the idle will stabilize, and the volt gauge will jump up to 14 volts. Once the engine has been revved, the alternator will charge normally and I can drive all I want. Weird huh.

Ive tested the battery, CCAs are just belew 400 at 65 degrees. That is a little low, but the battery has endured 3 years of my foolhardy abuse.

Once the alternator is charging, the only symptom is a slightly excessive output waveform.

I plan on getting a full size battery, and battery box that can be installed in the trunk, but Im short on funds. I have a feeling I will also be buying a battery around the same time.

What are your thoughts guys?

[Rucca]

weird but still an alternator problem

[IanS]

weird but still an alternator problem

Does anyone know if the voltage regulator is part of the alternator on these, or is it external/part of the ECU?

[stlwaco]

The alternator does not do a whole heck of a lot when at idle. My cavalier shows 12 volts at idle. If i give it some throttle, it will jump to 13.5 - 14 volts.If the alternator output tests fine at 2300 RPM, it should be fine. Try replacing the battery (It's cheaper and easier anyways).

[Jager]

you also might try turning on your running lights to put a load on the system this will force the alternator to put more juice in the system, but again best to replace the battery or at least hae he battery tested, 3 years may be the limit . if its not a sealed battery check and see if the fluid is low if so top off with distilled water and you may also fix the problem.

[IanS]

The alternator does not do a whole heck of a lot when at idle. My cavalier shows 12 volts at idle. If i give it some throttle, it will jump to 13.5 - 14 volts.If the alternator output tests fine at 2300 RPM, it should be fine. Try replacing the battery (It's cheaper and easier anyways).

The alternator used to charge at idle, and it still does once I rev it once. Its just on initial startup that I have issues.

you also might try turning on your running lights to put a load on the system this will force the alternator to put more juice in the system, but again best to replace the battery or at least hae he battery tested, 3 years may be the limit . if its not a sealed battery check and see if the fluid is low if so top off with distilled water and you may also fix the problem.

If I turn lights and stuff on before revving the car, it just kills the battery faster, but once the alternator starts charging, I can have my lights, radio, rear defrost, fans, and blower motor running without any issue.

It is a sealed battery.

[Vegascorbin]

The problem is in the alternator. The voltage regulator is internal to the Alternator and is not getting properly excited at idle. Do you still have the original panel bulb/meter in the circuit? it is required for the charging circut to properly function. If yo hav echanged it from original then put it back to orginal and re-test. I wouold just replace the Alt. if it was me. IF you are short of funds then just goose the engine until it starts charging. That will work for awhile but you will end up changing the alternator sooner or later anyway.

One other thought. What RPM are you idleing at? If your ide is set too low them bump it up first then re-test.

[Shift__BODOM]

The same thing happened to me. It wouldn't charge until I gave it gas. I thought it was the belt, and when I was poking around, I decided to mess with some of the connectors. I wiggled a connector on the side of the alt and bang, insta-charge. Turns out it wasn't seating properly or something (tab broken probably) and coming loose, and I guess the vibrations of the motor revving (about 2000RPM, not much) happened to wiggle the connector. I since pushed it down as hard as possible and no problems.

Check the connector if you haven't. If it doesn't fix the prob, you might need a new alt.

[IanS]

The same thing happened to me. It wouldn't charge until I gave it gas. I thought it was the belt, and when I was poking around, I decided to mess with some of the connectors. I wiggled a connector on the side of the alt and bang, insta-charge. Turns out it wasn't seating properly or something (tab broken probably) and coming loose, and I guess the vibrations of the motor revving (about 2000RPM, not much) happened to wiggle the connector. I since pushed it down as hard as possible and no problems.

Check the connector if you haven't. If it doesn't fix the prob, you might need a new alt.

I had the alternator out two weeks ago, everything was tight coming out, and I double checked everything going back in. I was having the issue before, and after alt removal.

The problem is in the alternator. The voltage regulator is internal to the Alternator and is not getting properly excited at idle. Do you still have the original panel bulb/meter in the circuit? it is required for the charging circut to properly function. If yo hav echanged it from original then put it back to orginal and re-test. I wouold just replace the Alt. if it was me. IF you are short of funds then just goose the engine until it starts charging. That will work for awhile but you will end up changing the alternator sooner or later anyway.

One other thought. What RPM are you idleing at? If your ide is set too low them bump it up first then re-test.

Are you sure the volt reg is internal? Some are external, or are integrated into the ECU.

Its not that Im super low on funds, its just that I dont like throwing parts at a problem, hoping it be solved.

The engine Idles at 850 when warmed up, as it has for the last three years.