90dodge

Ok, it's been a while since I've been on here and I haven't owned a first gen in a while. But today I scored a 91.5 D350 single cab with 157k. It's not perfect, but the price was right and its what I've been looking for.
So an hour into the 5 hour trip home I lost the speedo, and my gauges started fluctuating. The interior lights started surging. I had changed a couple external voltage regulators on my 90 1st gen, so I figured this is the deal. By the time I stopped I had no more juice in the battery and the trans wouldn't shift into OD with out some power. So I will be going and retrieving it in the morning with a trailer.
So I need some direction.
1. I have heard TPS.
2. A fuce able link of some sort burning out.
3. Bad ground
4. Alternator/ voltage regulator.

Where should I start with out just throwing money at new parts, which I don't have a lot of. Thanks in advance for any help.

mknittle

First thing I would do is check connections including grounds. Then have the alternator checked. there are a lot of people on here thet know more than I do about the 91.5 and newer trucks.

NJTman

Not sure if a 91.5 is different than 92 or 93, but the sticky has a lot in it to help

If it has no Speedo, I would suggest checking the fusable links after cleaning all grounds and swapping the asd relay (if equipped)

Philip

If it is a 91.5 it will have an external regulator. It will be located in the same place your old 90 was mounted.

TRENDZ

crank sensor gap, asd relay wires, fuse links. 91.5 should be intercooled, and have a ecm.

Alec

If it is really a 91.5, then while it is intercooled, there is no crank position sensor, and the "ecm" only controls the grid heaters. It does, however, have the newer style speedometer.

oliver foster

Alec nailed it.
Those 1/2 year production Dodge trucks are always just a little different.

Montana2x2

Speedo is also grounded through the ECM on a 91.5

90dodge

ok, thanks guys.

Ok, so its a 92, not a 91.5.

Checked grounds, and the fusible links and they are all good.

I'll have to test the alternator.

I've never tested an alternator. can I do this at home with a volt meter?

eljefedavies

Crank sensor. My 93 did the exact same thing.

NJTman

Why haven't you swapped the relays yet ?

Read this:https://www.dieseltruckresource.com/...0/#post2582204

j_martin

Yes

The large terminal not at battery......fusible link or wiring bad.

Check the voltage at the two small terminals.
1 at battery, one considerably lower no output = alternator bad
Both at battery, PCM or VR, or connections thereto are bad
Both at ground supply relay or wiring bad.

NJTman

My money's on FL's or relay's being bad. That's what I experienced.

(and you cannot judge their "okay-ness", by just looking at them) Mine was bad, and it looked perfectly fine. I removed the sheath on the FL wire, and it was so corroded inside that the contact wasn't there anymore. The exterior looked normal, no burning, no singe..... and there was no continuity in the FL. It was a dead short.



If the alternator wasn't charging, I would think the speedo would still work, no ?

90dodge

I appreciate all the comments on this guys.

Unfortunately with 12 1/2 hours away from home a day for work and kiddos at night I haven't got to really dig into this yet.

I did find tonight that there is a spliced in wire coming from the alternator. This wire runs back into the cab and to a small toggle switch under the dash. The toggle switch is grounded!

What it's doing when in the on position is grounding out the alternator and forcing it to charge.

When the toggle switch is on, and the alternator is charging it's not letting the Transmision stay in OD. But when I flick the toggle off, the trans shifts into OD and will stay there even when I turn the toggle back on.

I need to check my thermals still and clean some stuff up, but what I'm gathering is the Voltage regulator is bad.

j_martin

The voltage regulator is built into the PCM. What's happening with the PCM is it isn't running. PO installed a toggle switch to ground the PCM terminal on the alternator and full field it. That, by the way, is a good way to blow the top off the battery.

As to why the PCM isn't running. It could be one of the 2 power feeds to it. One of the feeds comes from the same ASD relay that drives the generator. It could also be grounding, and it could be missing the pulse feed from the CPS.

Here's my best guess based on analysis and experience.
Assumption 1. The alternator won't run with the switch off because the PCM wire to the alternator is disconnected and the toggle switch is connected in it's place. If there's two wires under the terminal with the wire to the toggle switch, I am wrong in that assumption. If correct, however, continue with the logic.

Assumption 2. When the alternator is fielded, a load is put on the ASD relay, maybe warming things up a bit near it.

Observation from experience. The wiring at the ASD relay is exposed to road spray. If it is pierced during trouble shooting and not repaired (a drop of liquid electrical tape on the pinhole) the wire inside the insulation will corrode until it parts.

Check the power at the ASD battery connection on the PCM (Pin 57) It is the dark green with orange tracer wire that comes from the same pin on the ASD relay as the DG/O wire to the alternator. Molest the wiring near the ASD relay while you check it. I think you'll find your problem. Broken wires under the ASD relay are more common than you might think.

Odds are the regulator in the PCM is fine. Hook it back up. I did notice you said the wire is spliced. If the PO originally grounded the wrong terminal, he may have blown the regulator circuit in the PCM. In that case you'd need to replace the PCM, or bypass it with an external voltage regulator, which isn't a big deal. The OD circuit should still run, though.

hope it helps.