woodrat

So, truck doesn't get driven much these days, but I dragged it out and have been elk hunting out of it. Charging system has been acting strange, mostly no charge, and then occasionally working. Came home last night on almost no headlights, almost dead battery. Threw it on the charger over night, and was trying to figure it out this morning.

I read a bunch of threads, and this truck fails the ASD test, no juice to either field connection when key is on. Swapped for the AC relay, same. So I tested things with a voltmeter. The wire that would normally just go to ground on a simple relay like this, the blue/yellow one, instead goes to pin 51 in the stupid PCM. The relay is not switching, and I keep thinking I should just connect that blue/yellow wire directly to ground so that this relay can do it's proper job of turning on the power to the alternator.

Is there a reason that this goes to the PCM instead of directly to ground? Doesn't this relay want to feed power to the alternator all the time when the key is on? It seems like if I just grounded that wire, things would be peachy, but I don't want to blow up this dumb box, or let the smoke out of something that I shouldn't. FWIW, pins 11 and 12 in the harness, shown as power grounds in the diagram, do show continuity to ground. Why would that wire need to go to the PCM just to get to ground? Why, oh why did Chrysler have to complicate this beautifully simple diesel engine installation by attaching one of their goofy black boxes to it?

I only have three more days to find an elk, including today! Help!

j_martin

According to the PCM diagnostic book, the only thing needed for ASD to set is battery voltage (pin 3) above 10 V.

Any other concurrent trubles, OD drops out, cruise drops out, tach to 0, etc?

Any diagnostic codes set. (key on, off, on, off, on......count the blinking light.)

woodrat

don't have a tach, or an OD, it's a five speed truck. Cruise hasn't worked reliably ever, and not at all for at least a year or more now.

Codes were 41 and 12, cleaned up the battery connections, no codes back on yet now. took the PCM connector loose, blew everything out, hit it with contact cleaner, blew it out again with canned air, and put it back, same with relay plugs. For now, the truck is running and charging again, been idling in the driveway for an hour and it's still charging, but I don't trust it to last long.

I think I've got enough battery to run and get fuel and still make a pass at the elk this afternoon, though, and if it will hang together for a couple more days, then I'll have time to really dig in again.

So, that wire that goes to 51 on the PCM is just a ground, then, and not something that the PCM is switching on and off for some reason? Wonder if the contact cleaner did the trick... I'll try the cruise on the way to town for fuel and see if that came back, too.

I've always been tempted to do the old mopar VR conversion. If I can't put this problem to bed, maybe I'll end up doing that.

I'll check in again later when I get back home. Thanks!

j_martin

Go to the music/guitar store and buy a can of Deoxit-D5 contact cleaner. Detail the connectors on the relays, sensors, PCM, and the in line connectors, especially the CPS connector top front, and the 10 pin engine harness connector under the intake manifold.

It'll be reliable then. Weak link is connections.

Some truckers bathe their harness connectors in WD40 with pretty good results also. I've seen the Deoxit fix connectors WD-40 couldn't.

For generator fielding, it needs 12V to the PCM, which sets the ASD. Then CPS signal which tells the PCM the engine is rotating. PCM then fields the alternator (ground side)

If I were you, I'd go hunting, pronto. Take yer contact cleaner with you.

woodrat

Ha, I tried, but I didn't even make to get fuel before it started going south again.

It was fluctuating just a little when I first got on the road, and the voltage varied with the RPMs, and then it settled down and was holding at a nice 14 v or so most of the way to town, 10 miles away. Then the fuel gauge, which has been only partially useful for many years, suddenly pegged out as max full, then dropped back down to nothing, which is more normal for it. Cruise control works now, though! Wow! Haven't had that for years!

I was almost to town, and suddenly the voltage dropped back down to 12-ish from 14 or so, and turning on the blinker made it bounce. Bad sign! Pulled in and fueled up and then ran the codes. This time I got 12, 41, 42 and 33. Came right back home, since I can't go anywhere in this weather without enough batteries to keep the wipers and defrost working at the very least. On the way home, the fuel gauge worked normally for a bit, and then swung all around and quit again.

Pulled in the driveway, shut it off and ran the codes again, same ones. Cleaned the positive batt terminal again, that's a weak link since the bolt is all junky and frozen, but it's not hard to twist it down on there very tightly. Then ran the codes again. Now I'm back down to 12 and 41 only. But the fuel gauge is back again!

With the truck running, I now have 12.28 at the battery and 12.27 at the big wire coming off the alt. I have 12.25 at one of the field wires, and .01 at the other one. Sadly, I'm gonna need more batteries than that for the afternoon/evening hunting, so I threw the charger back on there again, and came in to look up those other codes. If I can, I'll still check in on one of my spots that's only a few minutes away, and try to get back before I need headlights.

I know I need to get a new bolt for that battery terminal, but it seems like there's more going on than just that.

woodrat

if the cruise is working, doesn't that imply the CPS is working, too? Just curious.

woodrat

well, this wasn't in the service manual...

After hitting everything with contact cleaner again, to no avail, and still getting 12 and 41 codes (what is 12? cannot find it in the FSM..), I decided to give the side of the alternator a couple of firm but gentle whacks with the ratchet handle, and I was instantly charging again...

I have a feeling a new alternator might be in my near future, hope they're not too much made of gold. At least I can get up to the clearcut now and take a peek to see if that bull ever came back yet.

jerseybud

Code 12 is battery disconnect in last 50 cycles. Normal in every 88-93 Dodge gas or diesel with a ECM

woodrat

ah, thanks.

made it up to check on my elk, still no bull, though. Had to whack the alternator again before coming back down, but that seems to restore it. Fuel gauge is still all over the place, but CC still works like it should, maybe even better than it used to.

j_martin

Your readings at the alternator indicate a bad alternator, specifically bad brushes/open field circuit.

You've got full field voltage, connected to battery, and no current.

Code 41 indicates open or shorted field circuit.

Either your readings were wrong before, or you also had dirty connectors. Either way, the alternator is bad now.

Hunnert bucks off the shelf at Oreileys, takes about 30 minutes to throw it in.

woodrat

thanks. not sure why I could not get the readings to work with the ASD and the key on the first time, but later when I had the truck RUNNING and not just key on, it was clear that the ASD was working after all. I figured that the voltage varying with engine speed was a bad sign, too.

As long as this sucker can get me up the hill tomorrow at dawn, I'll deal with replacing the alternator later in the day. ;-)

This alternator HAS been doing its job for almost 300k as near as I can tell, so I've got no complaints there.

j_martin

It's possible the PCM needs the CPS signal to power the ASD relay. The ASD circuit is a vestigal carry over from electric fuel pumps safety in the gassers. It's redundant here.

Anyway, it's clear the alternator is bad. It's pretty normal for them to be intermittent, sometimes for quite a time, before they totally fail.

Charge the battery overnight. Carry jumper cables, park so a buddy can get to the battery if needed, and go get some meat.

woodrat

ah, that would explain it, and why the grounded side of that relay circuit went through the PCM instead of just straight to ground.

I've not been driving the truck much lately, but it has acted a little odd when I do, and has needed to be jumped with the tractor a couple of times lately...

Exactly the plan, thanks!

schamran

You can buy new brushes and bearings for your alternator, if it's not already too far gone. It would save you quite a chunk of change.

deanhinsley1963

I had mine rebuilt for 135.00 and they took it off and put it back on.