PCM issue? Bad ground? No tach, speedometer, alternator charge

[BigPapa]

I’d say it’s this one.

 

[BlameCandida]

I’d say it’s this one.

Yep, you're right. You know, I don't think I've ever seen that cable connected there. I wonder if it's been flapping in the breeze the whole time I've owned this truck. Also, the rest of the cabling seems to differ from the wiring diagram. I remember when I had my 98, the red positive cable ran over the radiator to connect the two batteries. On this truck, both batteries run down to the starter and meet there. I'll have to look at this more tomorrow when there's daylight.

 

[BigPapa]

On this truck, both batteries run down to the starter and meet there.

That’s not factory. All 2nd Gen’s came with a crossover cable across the top of the radiator.

 

[BlameCandida]

I tried pulling ODB codes with a code reader, but got a link failed message. I'm not sure if that's due to the truck or the cheap reader. I tried doing the key on-off cycle to pull codes, but nothing happened. I'm not sure if I'm doing it right. I'm cycling off-on-off-on-off-on and then watching for the check engine light to blink at me. That's not happening.

When I run the engine, I don't have check engine or gen light on, but the tachometer is low, and the speedometer is incorrect (showing 15mph when I'm parked). When I hold the brake down, the tach starts quivering, and the speedometer reads right (0 mph).... but the check engine and gen lights come on.

With brake:


Without brake:

 

[BlameCandida]

I dug out my Power Probe kit and tested the fuel shutoff solenoid. I tried grounding to both the battery and the frame to see if there was any difference. I was able to lift the solenoid, but not hold it in place. I then connected up the Larry B harness I received, and had the same result. When I apply power to the lift wire the solenoid comes up a fraction of an inch, and then if I switch over to the hold wire (without breaking connection with the lift wire), the solenoid drops. I'm guessing this is a bad fuel shutoff solenoid.

I still have yet to test the alternator. I guess I'm just using a multimeter to see what voltage is coming off the alternator?

 

[GAmes]

I dug out my Power Probe kit and tested the fuel shutoff solenoid. I tried grounding to both the battery and the frame to see if there was any difference. I was able to lift the solenoid, but not hold it in place. I then connected up the Larry B harness I received, and had the same result. When I apply power to the lift wire the solenoid comes up a fraction of an inch, and then if I switch over to the hold wire (without breaking connection with the lift wire), the solenoid drops. I'm guessing this is a bad fuel shutoff solenoid.

I still have yet to test the alternator. I guess I'm just using a multimeter to see what voltage is coming off the alternator?

How did you get from no charging, no gauges to the FSS? Did you bump the starter with the ignition and leave the key on? I'm baffled by the test you describe.

 

[BlameCandida]

How did you get from no charging, no gauges to the FSS? Did you bump the starter with the ignition and leave the key on? I'm baffled by the test you describe.

Well, I'm not sure how it's all connected either. When I first broke down last month, the engine just stopped and I coasted to the shoulder. When I tried restarting the truck, the starter engaged, the engine fired, but then when I released the key from START to RUN, the engine would die. So at that point I was aware of the FSS issue. I was not aware of the charging/gauges/PCM issue until a couple minutes later. I zip tied the fuel level up, and then continued driving. That's when I noticed that the tach and speedometer were not registering. As well as the GEN light and low charge meter.

So the sequence of events are:

Driving down highway
Engine shuts off, coast to shoulder
Attempt to restart engine - cranks, fires, doesn't stay on
Remove FSS, tie up lever
Restart truck
Drive to nearest gas station, notice lack of gauges
Continue driving home
Apply brakes, and notice that gauges read true when brakes are applied
Turn on headlights about an hour before I'm due home
Battery quickly drains, losing headlights

 

[BigPapa]

There’s a relay in the PDC for the hold up circuit. Swap one of the others into it’s place to test. The relay for the pull up circuit is on the firewall.

 

[Ozymandias]

I'd ballpark it to the ignition switch. No RUN position power supply.

 

[brucejohnson]

I'd ballpark it to the ignition switch. No RUN position power supply.

I'll second that choice. Makes more sense with the additional details in the supplemental review.

 

[BlameCandida]

There’s a relay in the PDC for the hold up circuit. Swap one of the others into its place to test. The relay for the pull up circuit is on the firewall.

I swapped in the brand new relay, and no change.

I will look into seeing if I have power to one of the fuses that is powered through the ignition (after I tie the fuel level back up).

 

[GAmes]

Have you checked the fusible link? Blue, from the factory, wire fastened to the + terminal, driver's side battery.

 

[brucejohnson]

We seem to be bouncing around in search of something. Getting back to the KISS principle...

Since the alternator (generator, or whatever it is called) appears not to be charging, we could start there looking for output, if any.

You may need to wrap a fine stiff wire on the positive probe of the voltmeter in order to make a connection to the backside of both of the alternator field connectors while the plug remains connected to the alternator while it is running. (Negative to case ground).

CAUTION: Don't get tangled up on the moving parts.

The PCM feeds the field coil, as well as the ASD relay. No power, no relay activity.


Now to find where the power is lost.

A little hard to bounce around the schematics on the laptop with all the splices and associated circuit detours.


Best to check both fuse continuity and available voltage at:


PDC (Power Distribution Center)

Fuse 3 - 40 Amp (Battery Power)

Fuse 4 - 30 Amp (Battery Power)


Fuse Block

Fuse 9 - 10 Amp (Fed through ignition switch START and RUN positions only)


After this it starts to get "more interesting".

 

[kenny61]

Did you ever find the problem mine is doing same thing