While driving my 99 F350 7.3 it died and I was lucky enough to coast home. No WTS light, no tach movement when cranking, no fuel pump, no CEL, Cranks great but no smoke or fire. New CPS & PCM still no lights or tach. Moved relays checked all fuses. WTF is wrong?

 

Optima batteries, Mean Green HD starter(cranks at 400 RPM), will not communicate with OBD2 code reader. What is the PCM Diode?

 

No tach movement.. Bad crank sensor?

This killed my 7.3 once

Edit: I see new CPS, my bad.

PCM diode may be to protect the computer from batteries connected backwards? Where did you hear the term?

 

Any progress?

 

Moved to the 7.3L forum.

Thanks John!

 

I put in a request to move this to the 99-03PSD forum.

I would be looking at the fuse box for a blown fuse. The heater in the fuel bowl/filter housings are known to short out blowing the fuse to the PCM, killing it. You will get the symptoms you described if in fact that's what happened.

Sorry, I can never remember what fuse it is. On some trucks it's #22, and on other trucks it's #30 I believe.

If the fuse is blown, unplug the heater on the side of the fuel bowl/filter housing, tape the plug so it doesn't short out again, replace the fuse and try again. Also, there's 2 plugs on the filter housing. One is for the heater, the other is a sensor for water. I don't remember which is which.

 

Installed a re-flashed PCM and no change. Checked fuses with a tester and found a bad Maxi 30amp in #24 underhood. Don't always rely on your eyes. Fuse looked good but tested bad. So I put a good maxi 30 in and try the key. Briefly WTS light goes on and back off, check #24 and its blown again. Pull #30 fuse inside and put a new Maxi in and turn the key on, good so far. try putting #30 back in and I hear some clicking under the dash, WTS light for a few seconds then done. Another 30 amp Maxi gone. My girlfriend was checking all forums she could find and came across one that had guys talking about this fuse and why does Ford put so much on one circuit? PCM, Brake Pressure, Glow Plug Relay, and a couple others. I found a 30amp circuit breaker fuse in the #25(power window) underhood so instead of blowing $3 fuses I put it in #24 and pulled #30 inside. Tried the key again and as I try reinstalling #30 brief clicking and I drop the fuse. Pick it up and try again and it goes in and WTS light comes on and stays on. After the light goes out I try to start and I get Tach response and oil pressure but no Fire. No smoke. Still have over 12 volts(Optima Batteries) after glow plugs & cranking a couple different times for 20 seconds.

 

Did you unplug the fuel bowl heater as asked above? Try that before turning the key with a new fuse in #30. If I recall that's the # for a 99.

 

Unplugged the heater bowl about 3 months ago. Got passed that problem. This time it had been blowing #24 Maxi fuse under the hood. #30 inside is involved somehow because Ford in their infinite wisdom has combined many things on multiple circuits. #24 underhood is a power point for too many components. #30 inside is the heater bowl, PCM and possibly others. I hate electrical Gremlins and I hate Ford Engineers twice as much. Had been a good truck. Got it at a great price but it is as useful as a paper weight right now.

 

Subscribing. Have a 99, haven't had this issue yet...good luck finding it out. Wish I could offer more suggestions but I got nothing.

 

Check the plug again and make sure it is not shorting out to ground or just bad wiring. Check the harness at the valve cover drivers side also. Move it around, some times those wires short also. Good luck and keep us informed.

 

2nd what Bonanza said.

 

What he said. The harness rides on top of the drivers side valve cover and is known for rubbing a bare spot on some wires and causing all sorts of issues.

 

Heard of bad glowplug relay back feeding & causing problems,not sure if it pertains to Your short circuit.

 

I am in the process of getting a fuel pressure tester and once I see what the fuel pressure is I will have more info. I will check that wiring harness. Seems that Ford F'd up with the wiring on this series of truck. I have read about tilt steering issues and turn signal wiring, Overdrive override button wiring, the harness you guys are talking about and probably others. Thanks for the helpful input and please keep it coming as I need help.