Weird alternator issues.

[Ultimatedsm]

Hey guys, I been having some little issues with my alternator. Here is the problem:

When I intially start the car its always charging at 13.8-14V ALWAYS! . After 10 minutes of driving, I notice the car starts to charge 13.2V. Now after 20 minutes of driving the car starts to charge around 12.5V and so on. The weird thing is after every morning its charging at 13.8-14V. I been getting this trouble code lately, it goes way and comes back:

1500 - Generator FR terminal circuit malfunction

Let me know guys what I can check for and do.

 

[Mitsu RacerX]

Its your Alt. going bad. Mine did the same thing. It would charge at 14 while at idle but when you drove it around it would lose charge. I took it to autozone and they checked it. Then I came to find out that Autozone is a PASS/FAIL test. They can not tell you exactly what volts its putting out. Sounds to me like its heating up and the regulator isn't working..

 

[Ultimatedsm]

has anyone tried to make a heatshield for these alternators. I noticed how close it is to the o2 housing. The wierd thing is, this is happening to a few people I know and they just replaced their regulators. The 12.5V I read after 20-30 minute drive is at my turbo-timer. I noticed when I hooked up a VOLT meter it was actually 13V on the dot.

 

[Ultimatedsm]

Does anyone else have this problem? Why our DSM alternators so shit?

 

[toybreaker]

The dsm charging systems are temperature compensated.

Chart for 91 dsm;

14.2 - 15.4 at -20*c (-4*f)
13.9 - 14.9 at 20*c (68*f)
13.4 - 14.6 at 60*c (140*f)
13.1 - 14.5 at 80*c (176*f)

These voltages are measured at the alternator output terminal.

The engineers build temperature compensation in, partly to keep from destroying the battery. On a hot daylight drive, there's very little load on the charging system. If the a/c is off, the hotel load (fuel pump and ignition) on these cars is less than 10 amps. If the charging system was to maintain a high charging rate out on the highway crossing the desert, the battery electrolyte would boil out/dissapear...ruining the battery, and generating a warranty claim. (satan hates those)

There are some simple tests that can narrow down if it's ACTUALLY a problem for you.

Start by measuring the voltage, engine off, at the back of the alternator, and compare that to the battery voltage.

Fire the car up, turn on the headlights, and turn on the a/c, remeasure both voltages.
Give a little rpm to make sure the alt can produce some current.

Take your voltmeter with you and retest the system hot.

I think you'll find the alternator within spec, and the battery a schoshe less. Anything more than a 1/2 volt less (loaded) should be investigated.

Now go to where you gadged power for your turbo timer and measure that. It'll probably be lower than the battery, and noticeabally lower than the alternator output.

That's the result of resistance in the wires, relays, connections and etc. An interesting characteristic of electricity is that resistance increases with any temperature increase.

This means that any problems with connections, etc...will be magnified by high teperatures. Resistance makes heat, and heat makes more resistance...and that makes for some pretty substantial voltage drop. Which will cause any remote voltmeters to read lowish.

I've chased this same problem on my 90gsx every summer. I run a vdo analog gauge package, on it's own dedicated circuit, switched with a relay. It reports low battery voltage on a regular basis, but I have yet to have an issue with lowish voltages. It will most definately report the system not charging, (indicates ~11ish with the alt NOT charging) but it also makes me wonder about the system a lot on hot days...

The moral to the story is any resistance in a connection shows up as a voltage drop.

Heat makes the reistance more noticeable/problematic.

The more connections, relays, wiring between the alternator and where you're measuring the voltage, the greater the voltage drop.

Maybe some one with real training in electrical systems can add to this, but the gist of my post is, it may not actually be a problem.

If every connection costs a little voltage, and you're measuring pretty far downstream, you could be seeing a believable number at that point in the system, adjusted for allowable voltage drop along the way.

As long as the alternator and battery are in the ballpark, you're probably good to go.

Good luck,

And, be glad you're not driving a triumph. Lucas engineers aren't smart enough to vary output by temp, they vary it by time/phase of the moon/temperature of the ale in the local tavern, who knows...it just varies...


[EDIT] Ooops just saw you had a code, that can't be good. I don't know much about the 2g systems. They do have some ecu involvement in the charging system, so I'll leave that one for the experts. I don't have any diagrams or troubleshooting info. on the 2g's...sorry...

You may be having an intermitent internal failure/bad connection.

I've had some trouble with the 1g alternators internally. The cheap chain store remans seem to have trouble with the straps/bus bars inside seperating from the diodes/voltage regulators...

scratches head...runs the other way...

 

[Ultimatedsm]

I noticed the hotter the car gets the lower the voltage. Yeah that code comes on sometimes then off. It can take weeks for the code to come back again. Anyone else have any ideas??