Still fighting electrical - charging situation

Hey all,

I appreciate the input from all in the other thread. I've done most of what was suggested, cleaned and checked cables, grounds, fuses etc. 1994 XJ 4.0L, auto

Took voltage readings. The numbers at the field terminals are telling me something is wrong, I'm just not sure what. Here is what I found.

Battery voltage - engine off - 12.6 volts

Engine running - lights off - 12.24 volts

Engine Running - Headlights on - 12.08 volts

Voltage across field terminals - engine running - 12.04 volts

Lying on carport, looking at back of generator. Engine running.

Right field terminal to ground - 12.08 volts

Left field terminal to ground .033 volts

B+ Terminal to ground 12.17 volts

B+ terminal to left field terminal 12.17 volts

B+ terminal to right field service terminal .012 volts

Now a dumber question. Looking at the picture in the FSM of the wiring going to the field terminals, is the block between the field terminals actually a fusible link? In the picture it looks like one but picture may be deceiving.

Thanks in advance. All input is appreciated.

if im correct either the left or right terminals one is positive the other is negative. all an alternator is. is a glorified motor.

Well, it already looks like a charging issue - you should have slightly higher battery voltage while running/charging than while not.

You should see ground (ZERO) potential at one field terminal - simply because the field works by being supplied voltage at a varying rate (by the voltage regulator) in order to maintain voltage/current output and keep up with demand. So, reading .033VDC is not so odd.

You should NOT, however, compare voltage readings between B+/output and either field terminal - simply because the field should not be energised past, say, 6VDC in normal operation (more typically four, IIRC.)

I'll have to see if I can't dig up my old book on charging systems (regulators have changed significantly, alternators have not, over the last 30 years or so...) and give you more information - but I'm almost inclined to say "shorted regulator" and/or a brush problem. I say "shorted regulator," because I don't recall that you should see battery voltage at the field terminals. I say "brush problem" because if you DO supply battery voltage to the field coils, you should see alternator output spike to the point where you start blowing something out! That's an old test to isolate charging problems - you short the regulator to B+ and watch the voltmeter, it should peg out right away. If it does, repalce the regulator. If it does not, replace the alternator...

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if the alternator is working shouldn't the voltage be at least 13v.

The voltage regulator on this rig is part of the PCM. I'm trying to determine if it is the PCM or another problem.

I had the generator out and bench tested yesterday, The guy tested it twice and it checked out good. He then tested a brand new one and the numbers were the same.

This one has my mind boggled! :confused1 What is the block that connects to the two field terminals, the picture is very confusing.

Thanks for the help.

From what I've seen, it's just a moulded rubber block that makes the terminals not move and makes them easier to handle - like the one on the start motor wiring.

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Do you have an FSM? If not, I have a 1994 - PM me a reminder, and I'll see about typing up some test procedures from my copy after I get some work done (later to-night...)

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I do have the 94 FSM but haven't found test procedures in it. I'll dig deeper and see what I can find.

I appreciate y'all taking the time to help!

Dug deeper in to the FSM and appears I may have found the test procedures. I'll be studying them but if anyone else has input on this I'd appreciate it.

Thanks again!

azdesertrhino said:

The voltage regulator on this rig is part of the PCM. I'm trying to determine if it is the PCM or another problem.

I had the generator out and bench tested yesterday, The guy tested it twice and it checked out good. He then tested a brand new one and the numbers were the same.

This one has my mind boggled! :confused1 What is the block that connects to the two field terminals, the picture is very confusing.

Thanks for the help.

Click to expand...

Your alternator is not putting out enough juice, The guy that tested it didn't put a correct load test on it. I can tell by the numbers you are putting up with your meter. While you put a new alternator in put in bigger wiring while you are there. Good Luck

As I recall, the engine computer controls the ground leg of the field winding. So you should see +12volts on the other side of the windings. Since you see ground on one side of the windings and +12volts on the other side, I think the engine computer and regulation is working. The alternator, however just isn't putting out enough voltage. If you pull off the connector and measure across the field terminals with the meter set to ohms, do you get anything or does it say open ciruit (ie bad windings or brushes).

Hey guys what's going on?

I have a 1994 jeep cherokee country i-6 and had a charging issue. I've found out my Autoshutdown Relay was bad and 2 60 amp maxi fuses were bad. I replaced that and she's runiing good!

Good Luck!

Peace, Scott

lawsoncl said:

As I recall, the engine computer controls the ground leg of the field winding. So you should see +12volts on the other side of the windings. Since you see ground on one side of the windings and +12volts on the other side, I think the engine computer and regulation is working. The alternator, however just isn't putting out enough voltage. If you pull off the connector and measure across the field terminals with the meter set to ohms, do you get anything or does it say open ciruit (ie bad windings or brushes).

Click to expand...

I'll pull the connector and read across the field terminals in the morning. Any idea what the ohm readings should be in a non powered state?

Jeepxj94,I've checked the auto shutdown relay and the fuses and all check out o.k.

Appreciate the help everyone.

After having the alternator bench tested by Checker auto parts and having it declared fine, reinstalling it etc etc I pulled it out again today. Took it to Tucson Alternator Exchange and found it was defective. Bought a new one and installed it, all appears to be normal.

Thanks to everyone for input and advice.

azdesertrhino said:

After having the alternator bench tested by Checker auto parts and having it declared fine, reinstalling it etc etc I pulled it out again today. Took it to Tucson Alternator Exchange and found it was defective. Bought a new one and installed it, all appears to be normal.

Thanks to everyone for input and advice.

Click to expand...

Somehow, I'm not surprised that a defect passed the Checker bench - I used to work at Kragen's (same chain,) and the whole chain isn't really up to scratch...

What was the defect, anyhow? Field connector?

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