Truck is a '97 F350 7.3 of course and I'm having quite a bit of trouble with the charging system. Originally when it all began I had a constant voltage drop while both at idle and while driving. Eventually lost the tach and started shifting early almost like it was in limp mode. Naturally thinking it was either the batteries or the alternator I had them tested. Alternator failed (no surprise there) but the batteries were good although they were six years old. I decided to go ahead and replace both and ordered a 130 amp alternator from DB Electrical.

I did the SD tensioner upgrade at the same time while waiting on the alternator to ship since I had it all apart. After getting it all put back together I was still getting a significant enough voltage drop that the new alternator couldn't keep up. After some searching I checked all the battery cables for continuity and cleaned all the grounds from the negative cables. Checked for burnt fuseable links off the starter solenoid and tested them as well. Tested the GPR and found it to be bad, so I replaced it with one from NAPA.

Checked the system again both with a multimeter and off the OBDII with the Torque Pro app and was still seeing a slight draw loosing a 1/10 of a volt every minute or so. All the while still not getting above 12.5 volts even after running for a while.

At this point I was fed up with it and took it to the dealer where they informed me my brand new alternator and batteries were bad. Although possible but unlikely three new parts would be bad from the factory. So I bought a 130 amp Motercraft alternator from the dealer and installed it and took the batteries back to my Cat dealer to have them tested. They tested good as well as the DB electrical alternator (go figure.)

So I put my batteries back in and now I no longer have a voltage drop but I'm seeing a constant 11.8-11.9 volts at idle and while driving at 1800 RPM, 11.7 volts with the headlights on. Transmission was still shifting early until it went through the range once then settled back to where it would shift normally.

Sorry for the long winded post but just trying to give as much info as possible. At this point I'm out of ideas....I just can't seem to get it back to 14V like it should be. Have anyone of you guys experienced something similar or what do you think I should look at next?

 

When turning the key to Run, not start, does the battery light in the dash come On? The alternator uses that bulb filament to monitor battery voltage. If burnt out replace the bulb.

 

No I haven't seen it come on at all throughout this whole process. However I am running LEDs in the cluster so maybe that's part of the problem? I'll put a standard bulb back in and try that.

 

Did these troubles start around the time you installed the LEDs, perchance?

 

i think hes talking about when you first turn the key on the light should blink on for a sec

 

I have LEDs in my cluster too and everything thing cycles like normal. Sounds like you have a place to start looking though.

 

Actually, when you first turn the key to RUN, the charging system failure warning light should come on and stay on until the engine is running. It should be on at all times that the key is in RUN, but the engine is not running.

 

That makes sense, I'm pretty sure that it has been working then as it should but I'll double check it to make sure before I start swapping bulbs.

Before everything else began, I was having some trouble with a few of the indicator lights when putting the LEDs in. Some would come on when the key is in run and stay on after starting which wasn't the case with the incandescent bulb. I got a few different ones to try but I haven't had a chance put them in yet. So for right now I've been running a mix of LEDs and incandescents.

I did have one LED get hot and short out in one of the illumination spots. Although I thought it was just a faulty bulb could it be possible that the cluster itself might be causing part of the problem or even running mixed LEDs and incandescents?

 

I just had this initial thought, would it be possible for his GPR to be sticking on? The GP's suck a lot of juice when they are running.

You must have something big drawing it down that much, that was my initial thought, and at minimum something you can rule out.

 

^^^^^ Stuck GPR had crossed my mind. I would double-check on the warning light first, however.

 

Finally had a chance to work on the truck again. Looks like the charging system warning light is working as it should. I also swapped the incandescent bulbs back in and they made no difference. GPR is also good, I can hear it clicking off and passed a test with the multimeter.

One thing I just thought about and haven't tested yet is the pigtail coming off the top of the alternator itself. How do you go about testing it?

 

Check for ohms as well. A cable can look good, but be bad enough to keep a vehicle from starting, and it will still pass for a continuity test. Also I've learned these old trucks HATE LED lights.

I have LED dome and cab lights. I tried making the turn signals LED as well, but when I turned the left, or right flasher on with out headlights I got one hell of a surprise. cab, marker, rear left/right, front left/right lights all flashed at the same time.

From what I learned (which I may be mistaken) you have to add a resister on the ground side of the LED's so the truck sees proper voltage draw.

What about the diode in the fuse box under the hood? It may be apart of the charging system, but I dont know. Cant remember anymore what its for.