Yesterday, after doing some work at my farm, when I left for home, my dash voltage showed 8 volts. My radio didn't have enough juice to power to keep it on and my ac was blowing very weak, which drew my attention to the low voltage. I then noticed my speedometer went out, odometer and tach went out. Occasionally, applying the brake, etc, would cause the tach to jump. Being 30 minutes from home, I knew restarting the truck would not be an option with dash voltage showing 8 volts, so I decided to drive home, (btw- the batteries started the truck strong moments before). While driving, everything seemed okay, except for a harder shift between 2nd and 3rd (which it seems like the transmission has kinda 'surged' at higher speeds lately), and the electrical issues, until a couple of miles from home, when the truck stalled and would only move when 'patting' the accelerator. I was able to limp until a block from home, when it died.I've recharged the batteries, load tested them, and they are strong again. I started the truck and it didn't seem to warm up 'right'. Upon stepping on the accelerator, I noticed smoke from tailpipe. Also, there was no power when 'reving' it up. I didn't drive it, but did proceed to test further.

Reading voltage directly at the batteries are 12-13 volts whether switch is on or not. When switch is 'on' the dash voltage drops to 8 volts. At the power distribution box I proceeded to remove each relay and maxi fuse with the switch 'on' (one at a time). I also tried switching the relays around, just to double check. Nothing affected the voltage reading on the dash, and the normal 'clicking' sounds were present for the gloplugs, etc. I also disconnected the hot wire on alternator, and the couple of things added to the 'hot' terminal (one at a time), with no effect on dash voltage reading.

After testing with the switch 'on' for an hour or so, I decided to reposition the truck and the batteries were drained. It's acting as if there is a 'substantial' dead ground somewhere.

Does this sound like a faulty PCM (power control module)? or maybe ECM or IDM?

Thank you, David

 

How old are the batteries?

 

Sounds to me like an alternator issue. You should have around 14 volts at the batteries (at a minimum 13.5) With it running. It sounds like on your ride home it was just running in the batteries until they died. Which could account for all the other quirky things you describe like with the trans. Cause if they aren't getting proper voltage they won't work right as everything from engine to tranny is computer controlled.

 

x2 on the alternator, or maybe the GPR has an internal short. I had that happen once. Check if the terminals on the GPR are HOT, like really HOT, after 5 minutes of running.

The IDM needs as much voltage as it can get to function properly. If something is dropping the voltage that low, it may be affecting the IDM causing your engine symptoms. Thats just speculation though.

 

Thanks for replying, Thomas. I may not have explained it well enough. With the batteries fully charged, I can switch the key to 'on' (not running), and the dash voltage instantly drops from 12 volts to 8 volts. The batteries test 12 volts with the key 'on' but are being depleted. I did load test the alternator and I'm getting more like 13 volts right at the alternator. It's only when I insert the key and turn it, the dead ground appears. I don't know where to begin looking, except what I've done.

 

Thanks cowmiler08, I switched the relays around last night and did notice it was warm. I'll check it again and see what happens. Regardless of the alternator being connected or not, the system voltage on the dash (while running) is reading about 8 volts. I have it idling now and will let you know if, or how hot the relay is. Thank you

 

Okay, I allowed it to idle 6 or 7 minutes and there are no relays or fuses in the power distribution warm. Even with the alternator disconnected completely, the fault is happening with simply turning the key to the 'on' position.

 

It surely sounds like you ran home just on batteries and everything just got weaker as they did. Have you checked all your cables running to the alternator and starter? Maybe something is grounding due to wear? My alt gauge drops when I first start it and stays low until the glow plugs kick off and the alternator catches up. I guess you could check to see if the GP relay is keeping power to the gp's all the time?

 

Disconnect the small wire on gp relay to isolate the gps from the rest when testing.

 

Well, I disconnected each lead going to the gpr (glow plug relay- looks like solenoid- on top of engine)... still no change. I've went through all the wiring best I could tell and still nothing. I missed something basic and I'm going back to it... I've disconnected both batteries and treating them independently, since connected in parallel they might pass the load test. The first one is recharging and I'll report what I find. Thank you all for your input. I'd love hearing more.

 

Well, I overlooked something pretty basic. When I checked voltage out of the alternator, there was none. Since it was new (actually rebuilt from a local alternator/starter shop), I assumed there was a fault in my system (which it could still be). The shop owner is ordering me a replacement 'One-wire' alternator that would prevent future system faults from messing up the alternator. Does anyone know of a down-side to installing a 'One-wire' alternator? Will my dash meter still function, etc?

 

I understand the theory on the One-wire alternator but fail to understand why you really need one. The gauge in the dash is just a volt meter so "Yes", it will still work. Your "battery" light in the dash won't work because it is connected to the old alternator wiring and is required to provide field current to kick start the old alternator into operation. The One-wire alternator requires a certain rpm to kick start it into operation (unknown). To be honest I've never heard of anyone on here using one but that certainly doesn't mean it's not a good idea.

 

You should have battery voltage at alt lug the bigger black and orange battery wire .if 0 you probably have a inline fuse blown ( maybe welder caused) I try to copy schamatic.

 

Here's the wiring diagram , shows fuse over by starter relay.https://www.ford-trucks.com/forums/a...9&d=1376697981