Hi, this is an issue that started about a year ago but now it winter it seems to be happening every time time..

When i start he van from cold the voltmeter shows its not charging and running off the battery.. i checked the batt volts and it proves the dash reading to be correct. After driving the van a while the volts suddenly kick in and the van will then drive normally until the next time i restart form cold.
After keeping an eye on it and few experiments it seems to me that once the water temp reaches hot.. (ie at the mid point of the temp indicator) the charging systems decides to kick in, if i turn off and then soon back on it still works fine but if i leave it off long enough for the temp to drop, even 10 mins, it wont work.

could it be that the charging system is getting a ground or feed from one of the temp sensors by accident? I'm not sure how i should proceed.

i understand the regulator is part of the ecu and i dont want to replace that unless im sure its gonna fix it.

i read somewhere that there may be an ignition switch that could be the cause but that doesent make sense to my findings.

cheers guys.

van is 93 b250 ram wagon 5.2 injection

 

I think Alloro's trick of warming the ECM/PCM with a hair dryer, and seeing if it then charges instantly after starting is warranted to see if the problem lies in the engine computer or perhaps the connectors leading into it.

All electrical issues require removing cleaning and retightening of all grounds. Battery to firewall, battery to engine, frame to engine( if it exists, if not, add one)

White or green corrosion on battery cables requires replacement.

I've had a reman'd alternator with about 400 miles on it decide to quit charging after I ran 3 batteries low over a few weeks Baja and then asked it to recharge them. I fully charged all three batteries via the electrical grid and was going to try for the border, and about 50 miles into the trip all of a sudden it started charging again. I figure the brushes glazed over when they were asked to pass so many amps onto thirsty batteries, or popped off the commutator under the load and got stuck.

Also there is the possibility of an intermittent connection in the fusible link, if it exists on a '94. Follow the (+) cable from alternator to the battery and somewhere along it's length it might have a section with a different diameter wire with a softer type of insulation. These are designed so that when the current is exceeded the wire fails inside the insulation, and it will look burnt and stretch out when pulled on. When 20 years old they can fail or become intermittent without any outward signs they have done so.

Mine failed in such a manner. Looked perfect from outside, and even had continuity after it was cut out and tested, but it was not passing any current when in place.

Also when you have the cables off the battery, remove and clean the connections on the back of the alternator and retighten.

 

Thanks for the guidance.
After checking the connections and wiring I decided to have a look in the alternator.
I found the problem! one of the brushes was stuck in its hole. the holes casing was deformed making it a tight fit for the brush. It must've been like that from new so as the brush slowly wore down it was unable to be pushed out by its spring to maintain contact with the shaft. i bent out the hole a bit bigger (which actually broke a bit of plastic off) and it can now move freely with the spring behind it.
As it was warming up with the engine it must've expanded just enough to make a connection and thus kicked in but was getting worse with each drive.
Its all working perfect again!
HUZZAH!

 

Weird. Good catch.