Alternator putting out low voltage/injector replacement

[BrandonMag]

I'm having a charging problem on the 1988 IDI in my signature: the alternator is only putting out about 13 volts max. Upon starting, the gauge on the dash (which is accurate, I've checked it with a couple of multimeters) will slowly climb up to about 12 volts. After warming up and driving the truck for a few minutes the alternator will not put out more than about 13.2 volts. My understanding is that it should be putting out between 13.8-14.2 volts in order to keep the batteries charged. I bought a new pair of batteries for this truck about six months ago and at rest they are now reading between 12.2-12.4 volts (a good resting voltage for a lead acid battery should be about 12.6 volts).
I've replaced the regulator and double-checked all of the wiring (and replaced a couple of wires that were corroded). I took the alternator into AutoZone and it checked out good. Given what I've done I suspect the alternator isn't 100%, but it tested fine. Any ideas?

 

[gnathv]

When you check your voltage output do you have your high beam headlights, fan speed on high, radio, and wipers on?

 

[BrandonMag]

No, nothing is on.

 

[gnathv]

Turn everything on and check your voltage, if it’s still 13.2 it’s good but on the low side. Let it run long enough for the glow plugs to turn off before checking voltage.

 

[gnathv]

You must be registered for see images attach

This may interest you. Your alternator is probably 60 to 70 amp output. If you do the 3g upgrade if your alternator needs replacing you pick up almost 100% amperage output. Then you’ll see about 14.4 volts charging with everything running.

 

[BrandonMag]

The truck has a manual glow plug bypass switch, so there's no current draw when the key is turned to the on position. I will check voltage with all of the accessories turned on.
But that still doesn't fix the problem: low voltage. I looked at the display on the tester at AutoZone after the test was performed and the screen showed 13.8 volts. I've taken the truck up to 3K RPM (once warmed up, of course) and I can't get more than about 13.2 volts. (After I had driven it a couple of days ago I put my hand on the alternator and it was HOT. When I removed it I spun the pulley and the bearings are a little noisy but not sloppy.) Is it possible for an alternator to test good but not put out the necessary voltage in the truck from 700-3000 RPM?
EDIT: I see @gnathv posted a pic, but it's a little small. Here's a full-size version:

 

[BrandonMag]

Any other ideas out there? I'd prefer not to upgrade to a 3G alternator if possible.

 

[gnathv]

The voltage difference you‘re seeing from the tester at autozone and the voltage on your truck is most likely the difference in load placed on the alternator. As load goes up voltage goes down. The load at autozone was probably less than the actual load on your truck. Your alternator will get hot charging, if your bearings are beginning to growl it’s telling you it’s on its way out. Find the parts for your swap and end the pain.

 

[BrandonMag]

The voltage difference you‘re seeing from the tester at autozone and the voltage on your truck is most likely the difference in load placed on the alternator. As load goes up voltage goes down. The load at autozone was probably less than the actual load on your truck. Your alternator will get hot charging, if your bearings are beginning to growl it’s telling you it’s on its way out. Find the parts for your swap and end the pain.

Good point. If it needs a new alternator I should upgrade.

 

[TNBrett]

Try disconnecting the ground from one battery and check again. Repeat with the other battery. perhaps you have a weak cell in one of your newish batteries

 

[DaveBen]

YES you need an upgrade 3G alternator. Your truck has more electrical load than you think and the current alternator is NOT keeping up with the load(s).

 

[1mouse3]

The 130a 3g will do more good than you think and will be able to see at night with standard headlights, it also cleans up wiring that can give issues.

 

[BrandonMag]

3G alternator is necessary. Got it.

 

[Old Goat]

130 amp 3G alternator install

OK, my stock alternator was making some nasty noises from the bearings, so I figured what better time to do what? MOD! I happened to have a 130 amp 3G reman off of a van I had scrapped (92 300 I6). One off of a Taurus will also work. Now if you are going junkyarding, you want to be able...

www.oilburners.net

Goat

 

[BrandonMag]

Thanks for the reference, @Old Goat. I scanned that article earlier today; it's certainly not a difficult upgrade to do. But one of the reasons (pretty much the main reason, honestly) I choose to drive these old IDIs is because I'm cheap. The 3G alternator is around $200. A 1G is under $100. Plus, I just remembered (from about 12 years ago) that there is an adjustable voltage regulator you can use in place of the standard fixed resistance voltage regulator. I installed one on my first diesel truck, a 1989 F-250. (It worked like a charm and I never had any problems with it for the following seven years I owned the truck.) Problem is, I can't find one now. I've got some feelers out to find a replacement. I'll update this thread with the information that I find.