I have a 1991 Ranger, 2.3 L, 4 speed manual, 2WD. Coming back from the airport after an out of town work trip, I notice the truck is not charging. An overnight session on the battery charger did not bring the battery up to snuff and the local parts shop tested and tells me it's bad. Replaced.

After a couple of hours of charge, truck starts up fine but still shows no charge. A voltmeter across the new battery shows 12.1 volts - engine speed makes no difference. A check of the fuses finds nothing amiss, so I pulled the alternator out and took it to the shop for a bench test. It too checks out bad.

So - a "new" lifetime warrantied rebuild is now on the truck - and you guessed it - no charge.

I've confirmed 12 volts at both sides of the #3 and #7 underhood power distribution panel, the fuses are good. While the block shows a field coil relay, that position is unoccupied and has no contacts installed. I've confirmed 12 volts at the orange/blue and orange/black wires at the "top" connector to the alternator. I have continuity to the 2nd connector of the black/white wire, and 12 volts at the yellow/white wire - what I understand to be the power to the field coil of the alternator - but still no charge.

It has to be something basic - but what am I missing?

Jeff Rees
'91 2.3L 4 speed Ranger

 

Did you have the "new" alternator tested before you left the store with it?

 

No - and hindsight says I should have! Yes, it could be defective - but I'm certainly hoping not. If I can't find anything else, I'll take it back tomorrow.

Jeff Rees
'91 2.3L 4 speed Ranger

 

yes do have them bench test the 'new' alternator. i have had the same experience.. bad right off the shelf.
you should see at least 13.8 volts across the battery at idle.

 

^+1 on having the alternator checked before leaving the store with it.

I know you said all fuses are ok, but you didn't say you checked the under hood/power distributon box alternator Field fuse, is it ok????

 

The under-hood power distribution box has two 60 amp fuses labelled "Alternator Power" - both check good. There is a position labelled "Field Coil" - but there is no fuse, no clips for one, and as far as i can tell, no wires in that position. The wiring diagram I have doesn't show a fuse for the 2.3L engine.

I've checked for voltage - I get 12V at the under-hood distribution and the alternator at the main connections. I get continuity and voltage at the black/white "jumper" between the two alternator connectors. The yellow/white wire - the one I understand provides the field power - goes hot when the ignition is switched on. As far as I can tell - and understand the system - the wiring checks good.

I'm going to take the rebuild back and have it checked this morning - we'll see where that gets me.

Jeff Rees
'91 2.3L 4 speed Ranger

 

Just back from the parts store - alternator checks out. Two different folks tested it a total of three times - passed all of them.

So - any other suggestions? I have voltage at the "heavy" wire connector and get a 12V at the yellow/white wire - what I believe is the field coil power when the ignition is on - BUT, no apparent output from the unit.

Ideas?

Jeff Rees
'91 2.3L 4 speed Ranger

 

OK, good trouble shooting & feeback. Your right, it seems the 91 2.3L, 2.9 & 3.0L are wired different than the 4.0L, which has a fuse for the field windings.
If the field windings are hot with the ignition on, then they should self excite if the regulator, brushes diodes, ect, are doing their thing, so I agree, it sounds like the replacement alternator may be faulty.

If it was faulty, have its replacement bench checked for output & load regulation before leaving the store with it & let us know how it goes.

Edit: Woops, you posted results while I was checking wiring diagrams. If its not outputting in the vehicle, then the field isn't likely getting the voltage it needs to self excite, so check the field connection for voltage with the engine running, as you may have a wiring/connection/under load voltage drop to the field windings.

 

I literally just came in from working on the truck and washed my hands. I pulled all of the fuses - all good - reseated them. Checked all wires/voltages - as previously reported. I put the rebuilt alternator - checked good this morning - back in - just as I've done before. Hooked up the wiring - just as before - BUT this time, when I start the truck - CHARGE!! A good steady 14V at the battery and a charge indication at the dash. Only thing I can figure is one of the fuse connections must have had that "critical" bit of corrosion and the repeated removals/seatings cleaned it enough to make the required contact. All of them were treated with dialectric compound every time I removed/seated them so this is the best answer I could come up with.

Thanks for everyone's input - and let's hope this thing stays "fixed."

Jeff Rees
'91 2.3L 4 speed Ranger

 

OK more good feedback, BUT now that its not acting out, about the only way to trouble shoot it, is to wiggle the wires/connections/connectors, to see if you can induce it to act out again, or wait for Murphys Law & you know when it'll likely kick in!!!!! lol

 

good you got it worked out. pulling fuses etc may have done it.. but could it be the alternator wasn't completely grounded ???? food for thought..

 

A rebuilt alternator I installed on an Aerostar came with new pigtails for the connections at the alternator. The documentation stated that because of amperage, the spade connections could get 'tired', and lead to heat and damage. The pigtails were to be butt connected to the existing wires.
I don't know the specific connections on this vehicle, but I would check the spades or whatever is internal to the termination to make sure that there is a solid connection and the current output will have a good conductive path to the load and battery. If loose, it could overheat and melt the plastic connector.
That same alternator had the nut holding the pulley to the armature unscrew itself, and fall on the floor when the owner parked on a visit. Said nut should have been torqued to the 90 # range... Got another replacement alternator at no charge. It was a pain to R & R as the bolts went directly through the altenator into an aluminum mount bolted to the block and there was little clearance.
tom

 

The "destructions" mentioned inspection of and possible replacement of the connections - but these looked good - no signs of overheating or damage - so I left the factory originals on the harness - but this is the best "explanation" I, or anyone else has come up with. I'll look into the rplacement connectors.

Thanks for the suggestion!

Jeff Rees
'91 2.3L 4 speed Ranger