Hi All,
I have had poor charging with my van for many years. This spring it was not charging at all and I discovered the alternator was cracked.

I have put in a new 120 Amp alternator, a new battery since it was due, and am still not getting a good charge. Van seems to run as good as it ever has but is only putting out 12 to 12.3 Volts (ie. nothing) when running.

I did some testing and determined the following:
R6 +bat wire back to battery is under 1 Ohm
R9 -wire back to battery is under 1 Ohm
R3 wire back to computer is under 1 Ohm
J2 wire back to ground is 5.6 Ohm
Alternator R3 to J2 terminals (field) is 3.3 Ohms

It seems that J2 goes back through the ASD relay and then back to the computer ASD B+ terminal. I am a bit fuzzy on this.

I have also noticed that my day-time-running lights are sporadic and they also come from the same terminal as J2, The DRLs won't turn the lights on but they will keep the lights on after I turn them off. I removed the DRL module, sanded the ground, and put it back on with no luck. I also disconnected the ASD relay and plugged it back in but again, no luck.

Please advise if there is any more testing I can complete to figure this out.

 

SteveR have you thought about adding a external voltage regulator kit? That way as know you can bypass the computer and the headaches associated with it. Here's link they also have informative videos:
https://store.alternatorparts.com/hd...ement-kit.aspx

 

Thank you, that looks like a good solution if I find that it's a computer problem. There is even some sort of device included that is supposed to trick the computer into thinking the alternator is still there and working which is nice.

I called the local dealer today and the Auto Shut Down (ASD) Relay is no longer available but they gave me the part # which is 56006904. That crosses to a few different aftermarket options so I'm going to replace the ASD relay.

I will also finish continuity testing the J2 wire as far as I can because it seems to be the issue if its not the computer or ASD relay. There's also supposed to be a ground near the ignition coil that I want to check out. Lastly, I'll try to run the field at full battery power just to reassure myself that the alternator is working and the + & - cables are working at high current.

The gas gauge has always read about 1/4 tank lower than actual and I'm thinking it somehow plays in to this. It is also associated with the J2 wire so we shall see...

 

Alright, I changed the ASD relay but no joy there. I also disconnected and reconnected all of the connectors I could find under the hood but that didn't help either.

The next thing I did was Ground the R3 pin on the back of the alternator with a heavy jumper wire while my wife watched the battery voltage with a multi-meter. Do NOT ground the J2 pin, that will probably damage something as it is the Positive feed to the field and you cannot test for this with a multi-meter. You leave everything connected when you do this test and just touch the ground wire against R3. You will see a little spark when you do this and the alternator will make a bit of noise as it loads up.

• With my starting & coach batteries connected the voltage grew very slowly, after a couple minutes I only got to 13.6 Volts so I stopped the test. The voltage drops right back down when you disconnect the jumper wire.
• With only my starting battery connected the voltage climbed very fast, I had to disconnect the ground from the R3 pin just after connecting it and the battery still surpassed 14 Volts. If you surpass something like 16 Volts you will start blowing bulbs and destroy the computer.

This testing tells me the belts are tight enough, the alternator works, and most of the wiring is good. I had previously confirmed that the R3 wire to the computer is good so the problem is between the computer Pin 20 (R3) and ground.

So, does anybody know where the computer is grounded? I don't have my manual on me at the moment and that seems to be the last step in verifying the computer is at fault.

The van has a 25/50 amp charger on board but it was unplugged for the last month while I've been picking at the alternator. I checked the electrolyte level in the coach batteries and put them back on charge so they should be good tomorrow.

 

Doesn't the 91 have an external voltage regulator???

 

It does now, but not originally. I am going to go over what I've done with a few different posts.

Here are some photos of the under hood grounds. There is another one under the van in front of the fuel tank and there is at least one under the dash.



Rear of passenger side head


Front ignition coil mount


Part of 4-way alternator connector


Down by starter relay


Passenger fender


Behind battery


Behind passenger side loom near HVAC box

 

I went ahead and disconnected each ground, cleaned it with emery cloth, and put some copper paste on the connections. None of this helped. The van was just running off the battery without any charging taking place.

The computer must be grounded through the pins or the large bolt holding the connector on. I had a peak inside because sometimes you can find damaged traces on the circuit board. This one has a tropical potting compound on it which is not aging well. I am going to have to order a new computer but vacation time is coming and I needed a sure-win so I ordered the external alternator regulator linked above.



Air from the intake blows through the computer cavity.


The silicone potting is not doing too well.

 

Installing the external regulator is not too bad. I decided to mount it to the firewall on the drivers side because I could visually confirm none of the screws would come through and poke into something.

The regulator has a few wires to be connected.
1 black wire which joins the ground lug on the regulator with the ground lug on the alternator. This is just a loose black wire you put connectors on.
1 black/red pair which join to the field. My alternator has a 4-way molded connector so I chopped these wires about 4" from where they enter the connector.
1 red wire which needs to be connected to a key-switched positive feed. I need to figure out where I want to connect this still.

I augmented the kit with a big of paired wire from some trailer wiring to connect the device which is used to trick the computer into thinking the alternator is still being controlled by the computer. I did this so I could locate it beneath the regulator. I also replaced the loom with some mesh and used double-walled shrink tubing, this is just my personal preference.



The kit


Voltage control on the back of the regulator. Better potting compound than the computer.


Alternator simulator.


4-way connector, chop the two smaller wires.


Wiring in the regulator to the 4-way connector side of the two wires.


The brown/yellow wires go to the harness side of the two wires.


The lone black wire is connected to the alternator ground lug.

 

The van is back on the road, I found an accessory plug to power the regulator under the dash which is meant for conversion vans. I suppose the only thing I don't like is that the Regulator is pumping full power through the alternator field when the van is OFF but the ignition on in an attempt to raise the battery voltage. I took a nap in the van while the wife was shopping and the regulator was quite warm after an hour with the radio on using the accessory key position. : I am going to research the ASD relay a bit more and see if I can use it to run a relay for the regulator instead of using direct accessory power.

I figured out the daytime running light module I had mentioned earlier. It won't kick on the headlights until the vehicle speed sensor picks up movement but the headlights are one for good after the initial movement.



The circuit breaker is for the trailer brakes and is unrelated.


Battery and Accessory connectors. I didn't have the correct size connector to stick in to them so I can the end off the wire.


Hooked up.


14.3 Volts as advertised. The system drifts a bit when you come from high RPMs and back to an idle but that is expected.


Just above the 2nd tick.