2nd Gen Non-Engine/Transmission Voltage problem....

[Curious Dave]

Okay guys... needs some potential brainstorming here.



I realized today that my stock voltmeter was showing no voltage. So I stop and replace the darn thing. At idle it works fine. . Driving down the freeway 5 minutes later the gauge goes to the bottom again. All wires are connected, tight, and clean. I had the old alternator tested and it tests good but has a loose positive tower.



I get 50 miles down the road and the truck starts with a functional gauge. No more discharge. I haven't driven anywhere yet to see if the gauge is working or not. I have an ECM coming. I was told this is what the problem was. I am not sure.



What do you folks think?

 

[WilsonF]

You replaced the volt meter or the alt? If the alt. does your tach work? If not could be the crank censer. It also could be just the part of the ECM that controls the alt. If you don't want to spend big bucks on a new ECM,do a search, you can add an external voltage regulator that will control you alt.

Floyd

 

[Curious Dave]

Floyd,



The tach still works. I'll try to find the post on the regulator.



Thanx

 

[n7gxz]

The ECM does not control the alt, it is the PCM.



Kevin

 

[Curious Dave]

OK... update... . I put on another alt. from O'Reilly's. I get a jump. I see while I am idling that the volt meter is a little low... but functional. Away we go... . I get on the freeway and the darn gauge quits again. I decide to push my luck as all of the acc. 's were working fine and the aftermarket gauges were reading fine. I went the 50 miles to where I needed to be and park the truck. I decide to try to start it for kicks. She started perfectly. Gauge still doesn't work.

I let her sit all night and try again in the morning. She starts fine and the gauge is reading 14v. Another 24 hrs later and @ 50 more miles and everything is fine. I am wondering if something got overheated and freaked out. Now that it is cooler... everything is ok.

Sound right? Possible? Realistic?

Please let me know what you guys think.

 

[WilsonF]

OK, what he says.
Try post #19 in this thread: http://www.dieseltruckresource.com/dev/truck-no-charge-y-t192798p2.html
There may be something else there that might help you.

Floyd
You slipped you new post in whail I was typing. Still some good reading.

 

[Curious Dave]

Floyd,



I found that yesterday. It is a good one to hold onto that's for sure. Thanx though.



Dave

 

[DodgeWarlock]

Okay, so along the same lines. Our 01 started acting up the other day. Wife drove it to work and all is fine. When she left after a short distance the voltmeter goes to nothing and the check guages light comes on. She babies it home (about 10 miles) with no problems. When I go to check it out, it shows 14 volts at idle for like 20 mins. Take it for a test drive and after about a mile it drops again. Same test, no drop at idle, but just rev to 2000-2200 rpm's and hold and it drops.



Here's the screwy part. Checked voltage at alternator and both batteries and get 13. 67 volts at all times when running. Get 12. 62 on batteries when not running, so alternator appears to be charging fine. My first assumption was just a bad guage. But now, I'm concerned the computer may not be getting the correct voltage. If it was not for fear of damaging the computer, I would just drive it and install a seperate temp voltmeter.



Any ideas? We recently moved and I'm searching for my FSM's but, could use some advice.

 

[WilsonF]

When my Alt. went out it was erratic, work sometimes an then not. After many mis-steps I rebuilt my Alt. including bearings, brushes, diode pack and slip ring. The system works great now.

Floyd

 

[DieselDoghouse]

Fine at idle but chokes at road speed?? (reference down the highway) I'd check the slip rings to the rotor for sure. Changing rotational speed could be causing the connection to fail - no excitation to rotor = no output from stator windings!!

 

[DodgeWarlock]

The alternator is charging steadily at 13. 67, but voltmeter goes dead and light comes on. My assumption is that the voltage regulator circuit in the computer is good since it is charging at a steady voltage. If it was just the voltmeter, I would not be too concerned. It would simply look like a bad guage. But where does the signal for the light come from? Is it triggered by the computer or the guage?

 

[Hammer]

Signal is tripped by the computer and the alternator is internally regulated.

 

[Curious Dave]

Does anyone know where I can get some explanation as to the design and build of the system?

 

[DodgeWarlock]

Signal is tripped by the computer and the alternator is internally regulated.

So should I be concerned about underpowering the computer and possibly damaging it? Or does it use a seperate power feed for the voltmeter/light signal source and the computer's power feed? Sorry, I could probably figure this outon my own if I could find my FSM. But after a week of searching, no luck.

 

[DodgeWarlock]

Finally found my 01's FSM's. Man do the wiring diagrams stink. They were obviously drawn up by someone who doesn't use them. The voltage gauge is not even in the diagrams. So the alternator is externally regulated by the voltage regulator in the PCM.



After some follow up testing with an extra set of hands the voltage is dropping off at road rpm's. But it comes back up at idle, even though not shown on the gauge. Turn the truck off and back on and the guage and light reset. My Napa guy and my local alternator shop both believe it is in the PCM. I guess the next step is to take the alternator off and take it for testing.



If it tests ok, I'm going to look into adding a stand alone regulator as linked above. I see no reason to pay big $$$ to replace the PCM, at this point. Anybody else tried this approach so far???

 

[Curious Dave]

Sounds similar to the way mine started out... But it seams to have gone into remition. I may have to do the old school regulator as well. Let me know how it works for you.



Dave

 

[Road Dog]

The voltage gauge is not even in the diagrams. So the alternator is externally regulated by the voltage regulator in the PCM.

The voltage gauge -- and the rest of the instrument cluster -- is electronic. It receives data from the PCM/ECM and isn't directly connected to anything. There's a self test for the cluster by keying ON OFF ON OFF while pressing the odometer button (or something like that). If you check the PCM error codes (another ON OFF ON OFF sequence) there's a low voltage code. It could be bad grounds, bad battery, bad battery terminal connections, bad PCM, who knows. If you wire a voltmeter into the cig lighter then you can see the actual voltage.

 

[kscheffler]

13. 67 at highway RPM is too low should be reading 14. 2 to 14. 4 some thing is wrong with alternator or voltage regulator. It could be a bad ground check all your connections.

 

[DodgeWarlock]

So, finally got the chance to take the alternator off and haul it 20 miles to get it tested. NAPA did not have the right plugs to test it(they have since ordered them).



It took 4 guys at the new O'Reilly to test it. Then they said it failed because the voltage regulator was bad. This led to an argument because when I told them it was externally regulated(in the ECM), the manager said I did not know what I was talking about.



Took my business to Autozone, where they tested it correctly and it failed. In addition to the output failure, the bearings (which you could not hear over the 24v) sounded like a cessna on the test stand. Unfortunately, even though they showed the matching Bosch unit($260) it was a 2 day wait to get it.



Went back to Napa where it was 1 day out, but cost more($330). But after crossing the Chrysler part number(it was the original alternator)it crossed to a Nippondenso($180). The output specs were the same, so I gave it a try. The new alternator fixed it.



Thanks to the folks at NAPA for taking the extra time to research it out.



And thanks for the input from my fellow TDR members.