Intermittent Charging Problem

[sdiddy919]

Hi All,

I'm having a strange electrical problem. My van is a 1994 B250 with a 6 cylinder. The voltage gage is moving around and I get the check engine lite with a code of 41. That means a low voltage condition (< 11.75v) has occurred. The alternator was checked and it is ok. I cleaned all the contacts on the alternator. I also replaced the drivebelt tensioner and still have the same problem.

The voltage gage starts out at 15 volts, but then as I drive, it starts fluctuating untill it is below the 11.75 volt threshold and the check engine lite turns on. Anyone have any clues as to what I should check next?

Thanks in advance
Steve

[Dodgevanman]

The large black wire coming off the alternator (about a 10 guage wire) is protected via a fusible link. The fusible links are up by the bulkhead connector near the battery. It's possible that the fusible link is blown. This would keep the alternator from charging the battery.

Also, the ECM controls the voltage output of the alternator (acting as the voltage regulator). Hopefully this circuit is okay, because it would mean ECM replacement if it isn't.

[alloro]

The voltage gage starts out at 15 volts, but then as I drive, it starts fluctuating until it is below the 11.75 volt threshold and the check engine lite turns on.

It's a bad alternator. I know you had it checked, but what's happening is it's failing as it gets hot. When it's being tested it's likely cooler than after you've been driving for a while, so the test comes back saying the alternator is good.

[sdiddy919]

That's interesting about the alternator getting hot then failing. For a while it also seemed when I put the brakes on, the voltage would shoot up too. Have you seen a case where the alternator passes a test when cold but fails when hot?

Also, are there any checks that can be performed to rule out the PCM and voltage regulation?

[alloro]

Have you seen a case where the alternator passes a test when cold but fails when hot?

Only if tested in the vehicle when it was hot.

[sdiddy919]

Well, I don't think it is an overheating alternator. The van sat for around 8 hours in the parking lot in 40 deg weather yesterday. When I started it up the voltmeter gage still read low. I'm suspecting a loose or corroded connection or the fusible link. Now to do the searching, which will be fun.

Anyone know where the main wire on the alternator goes?

Thanks in advance
Steve

[sdiddy919]

Well, it turned out to be the alternator all along. I took the alternator to a rebuilding shop. The shop rebuilt the alternator in about 4 hours and charged me $90, which was cheaper than buying a new one from AutoZone.

I got a false positive from the AutoZone tester, probably because they only go up to 300RPM and the alternator shop can put a much larger load on the alternator.

So, the van is running again...

[alloro]

Who woulda thunk it. ;)

[Dodgevanman]

Strange.

Glad you got her fixed. That's a darn good price too!