At least when the truck wouldn't start I was only a few blocks from my house getting coffee, not driving down Highway 5 like I was yesterday.

The voltage on my dash gage looked like it was under 12v, and the lights on the dash where a bit dim, so I think DUH, is in order here/

Where do I start. Did the voltage regulator die or did the alternator?
I have the truck in the driveway on a trickle charge so I can start it to test, but other than buying a new regulator I don't actually know what I'm supposed to test. I have meters, and am ready to start sticking probes where needed.

Thanks in advance for any help
-mickey

 

If the 91 is the same as a 90, the regulator is integral with the alternator. If you can get it started and have a volt meter, put it on the battery and you should have 13.5 to 14 or more volts. The alternator is not that expensive and about a 15 minute job...Mark

 

Actually, the regulator isn't internal to the alternator on any of the diesels. If it isn't mounted to the firewall, it will be an internal part of the PCM.

 

Carefully check the battery (+) at the rear of the alternator with the engine running it should be about 13.8 volts at a fast idle, make sure the regulator is plugged in at the firewall, wiggle all of the wires to make sure there are no loose connections.

It is easy to just pull the alternator and take it to Auto Zone, or Pep Boys and have it load tested, when the brushes wear down it will stop charging.

If you are getting a good 13.8 volts at the alternator but not at the battery then check the large connector about 8 to 10 inches down the wire from the alternator.

The charging system on the earlier trucks are amazingly simple.

Jim

 

Excellent info, thanks!

 

Another common problem is that the battery terminals themselves get very corroded. If they are it will not properly charge the battery. But our system is very simple. On a seperate note is there any other items not working? Such as ac? Remember it all needs the crank positioning sensor to be working to tell the ECU that the truck is running for the charging system and ac to work! RAM

 

'91 has no crank sensor.

 

I do not mean to hijack this post, but I am confused. I was under the impression that the only computer on my 90 is the one for the RWAL. Where is the PCM and what does it do...Mark NEVER MIND When all else failed I read the FSM. When I first got the truck it had charging problems, so I replaced the alternator. I looked around for a regulator and when I didn't see anything that looked like a regulator, I assumed (I KNOW, I KNOW) that it was internal. I do have to say, between the fact that it had been painted over and the fact that it really doesn't look like a regulator, it was an assumption easy to make (excuses, excuses). Soooooooo, when I get back to the the USA, I am going to replace my regulator, because, I believe, the alternator and regulator should always be replaced as a pair...Mark

 

Your '90 (like all other non-intercooled trucks) has no PCM. It does have an intake heater controller that runs the intake heaters (duh) as well as the KSB and the WIF light. Kinda like a really dumb PCM, it is mounted on the firewall below the brake booster.

In late '91 the intercooled trucks began using a simplified PCM (between the battery and the fender) to control the intake heaters, the WIF light, and OD. KSB control was changed to a simple temperature switch. The '92-'93 PCMs added A/C clutch control, cruise, and the charging system.

 

It's stopped raining finally and I'm about to get out and test things.
In the mean time why is there such a big difference in price between regulators?

The local parts store here is Kragen (O'reilly) and I see BWD for $40, or Neihoff for $18.
?

 

Maybe the warranty? Neihoff has always been good to me and I have had more failures with Borg Warner products for some reason.
Make sure to have the alternator tested also.
OEM would be better though but more expensive.
Jim

 

get the blue reg from dodge about $30 .worth it

 

The blue regulator is not temperature compensated.

I would suggest OEM from the junkyard (any Mopar product from the mid '70's up through the late '80's) or the AutoZone house brand.

 

The worst, intermittent.

So I started it up. checked at battery, and got 12v.
I turned it off, and fiddled with the wires a little bit, started it back up 14.7 @ battery.
I turned it off, loosened up all the connections, sprayed with contact cleaner scrubbed with brush, and started it back up. 12v
I pushed the connector attaching to the Voltage regulator really hard to make sure it was seated, and got 14.7 again.
Now what?

 

Replace the regulator and the pigtail.