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I have a 1991 Plymouth Voyager 3.3 . I was driving and my check gages light went on and my voltgage gage went to zero. So I purchased a new alternator and that didn't fix the problem.

I recently discovered the ECM controls the voltage regulation.

Yesterday I checked my connections , both connections at the recitfier have continuity to the ECM connector. Could the ECM be bad ?
Thanks!
John
 

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Could be. Do all accessories in the car work?

There are high current fuses ("maxi-fuses") underhood that are typically 60 amps and protect the alternator. Check all of these before going further.
 

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Does not this system control field (regulator) by making available ignition power at one brush terminal, then modulating the field output (to negative) through the ECM? If the alternator battery stud has power, and one of the field connections has power when the ignition is switched on, then I would hunt from that point on. I never forget that there exists a possibility when all the tests have been passed that a "new" alternator may be defective. I hesitate to recommend full fielding this type of alternator even at idle due to the possibility of load-dump harming the ECM out-of-hand. An old fashioned tail light bulb makes a great temporary field control after all the tests above indicate an inoperative regulation circuit. Disconnect the brush connection entirely. Both wires and set it safely aside. Use a jumper test clip wire to bridge from the big battery stud to one brush clip. I use an 1141 bulb with a pair of 12" test leads to connrct the second brush lead to nrgative. Beware of shorting the two test clips connected at the alternator, together.

Start the engine and let it idle. Immediately consult either a test meter or the dash gauge. Then shut off the engine.

If the voltage rose the problem lies between the alternator field to ECM connection. If it did not, there is another problem.

Again, make absolutely certain that there is battery power at the main alternator output stud before you test. This pre-test is by far the most critical one to be made when diagnosing an alternator "no charge" fault.

Hope this helps. Computer ECM gurus tell me the MoPar reg is very very beefy.
 
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I did replace the alternator twice . The first one I did the test you described and when I grounded the one terminal to battery voltage went up . I do have power at the battery terminal on the alternator also.

The accessories work fine! I couldn't locate any " maxi fuses" i just have the one fuse panel in the lower dash inside the van.
Thanks! John
 

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i would then (sigh) trace the field wire from the alternator to the ECM connector, disconnect the plug at the ECM and then use an Ω ohm meter to verify extremely low resistance between the disconnected field terminal, and the pin on the ECM connector harness.

Does your vehicle have the ECM in which loss of alternator (fault code) cause problems like loss of overdrive, engine management goes into open loop?
 
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I didn't get any fault codes? The van ran fine ,it went out on my to work . It made to work without any issues other than the gage going to zero after the check gages light came on.
It was hot outside so I was using the air conditioning. I will trace the field wire down again and check resistence! Thanks!
John
 

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I didn't get any fault codes?
I would think that the PCM (powertrain control module) would show and store diganostic code 41 which is a problem with the alternator field control circuit.


I would use a volt meter and check the voltage at the battery with the engine idling. You should have about 13 volts. Anything less and there is insufficient charging. If you have 13 volts then the system is charging and there is a problem in the instrument panel with the voltage gauge or the insrument panel wiring that goes through the firewall on the driver side.
 

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Good point. Recently my voltmeter went to zero.

The gauge pins were not making good contact. I took the plastic cover off the instrument panel, pressed on the gauge and it worked.
 
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I don't always trust gages in the vechicle . I have been using a multi meter and I only get battery voltage nothing over 13 volts.
 

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You can go to autozone.com and review wiring diagrams for your mini-van. You have to register and then search and find the diagram for your specific vehicle.

There are 2 wires on the alternator field. One is a dark green. It connects the negative side of the brushes to the PCM. You need to check that entire length for continuity up and through the connector at the PCM.

Twelve (12) volt power for the positive side of the alternator brushes comes from a dark green / orange tracer wire. It originates at the ASD (automatic shut down) relay and powers the fuel injectors and coil. You need to check for 12 volt power on this wire at the alternator. You will have to disconnect the ASD relay and jumper it as the relay is only closed when the engine crankshaft is rotating.
 

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Probably a stupid question, but did you have that alternator bench tested before you bought it? As a PSM for Autozone for five years, I learned shortly after going to work for them to check every alternator before I sold it. Several times I found defective ones right off the shelf. That may have happened to you. As a side note, I have not worked for Autozone since 1998.
 
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I checked the fusible links! Thanks! I found nothing that was bad. I have went through the wring checking, cleaning grounds. The only thing that doesn't work is the that the green wire form alternator to ECM . It won't ground the feild to charge. the green wire does have continuity from alt. to ECM. when I use a jumper from the field to battery gound the voltage goes up. So I ordered a new ECM.
Thanks for all the input! John
 
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Put in new ECM in today 14.1 volts! Thanks again!
 

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Put in new ECM in today 14.1 volts! Thanks again!
Interesting. Usually the ECM partial failure is NOT the reason for the no charge condition. You have to be thorough and check all other avenues before changing an engive control module. But this proves it can happen. You were thorough and removed all other causes before replacing control modules. Glad that it is fixed.
 
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