As an intro to this forum I've attached my 1997 F-350 Crew Cab Long Box 7.3L PowerStroke, POS edition. I've since put a bed on it and ripped out the interior to inspect the wiring harness and throw out all the broken bits.

I tried briefly to get the engine to start, but it only ever cranked. I've gotten side tracked by the lack of data/connection over the OBD2 port, despite it having power. I pulled the PCM and inspected it but didn't see any leaking/damaged caps or corrosion. The thin clear film coating the PCB has dried out a bit and is cracking, but there's no obvious corrosion. I did some reading and found a missing diode in the engine compartment's fuse box.

I'm hoping folks in the forum can point me to the correct part number for the diode that exists in the engine compartment fuse box. I've attached a picture of my engine fuse box, which is missing the diode that is supposed to populate fuse position 12. I'm having a hard time determining the part number for that particular diode. Based on internet sleuthing, the part number is either F2TE-14A604-AA or F5TZ-14A604-A. I'm able to find replacements online for "F5TZ-14A604-A", but not "F2TE-14A604-AA". Can anyone confirm which diode part number is required? My understanding is the diode is required to complete the connection to the PCB. Any suggestions on where I should buy these diodes?

 

Those diodes are common to many trucks and vans. It only protects the coil on the PCM relay and very little power flows thought it. Any similar diode will work. Pull one from a truck at a self serve junkyard. Or any of the part numbers you have will work if they fit in the fuse box.

The diode protects against connecting the battery backwards and frying the PCM. If you are brave you can jumper it for testing.

Here is a resource for wiring diagrams.
https://charm.li/Ford/



I'm

 

I will grab mine, 10/95 build I think so 96MY

Why not just jump PCM and IDM relays? 30 to 87.

 

F2TF 14A604 AA

10/95 build, 96MY OBD2 compliant

 

My 01/92 4.9 has - FOVF 14A604 AA

Same style fuse boxes so it would probably work too.

 

I've been looking through that site but I don't know how to read the circuitry diagrams nor do I know how a diode works. Still learning here so I'll keep at it and see if the diagrams start making sense to me eventually.

Thanks for pulling that part and verifying the number for me. My local junkyards have slim pickins for these fords in general. Very few F/E series and no Broncos.

Do y'all think the OBD2 port should work if that diode is not slotted in? Maybe the PCM is bad, which is causing the no-start? That's a guess as I don't know what all is exactly required to get the PS to turn over. I'm in the process of replacing all the sensors, but I expected the OBD2 port to work with my Windows 10 machine + FORscan + OBDLink USB reader ( ), even if the engine was off.

I guess what I really should have asked first was why won't my OBD2 port work? Any help here is appreciated. The truck is in very bad electrical shape, so I don't consider anything reliable at the moment.

 

Well, does the cig lighter work? That powers the OBD port

Why replacing all the sensors? Compression good at least? Starter age? Batt ages? Plug it in and jump those two relay. Hell, the GPR might be bad too.

A didoe allows power to flow in one direction, think of your kitchen tap. Its job in the fuse box is beyond me.

Also physically verify ALL fuses, mine had piles incorrect. If you have a junkyard close go grab a sandwich bag full especially those giant guys. They are very expensive

 

Per the circuit diagram, you need that diode to power on the PCM. You can temporarily replace it with a jumper or a generic diode. Its primary purpose is to protect against reversed battery terminals. Any diode from another vehicle that slots in will work. For this application, any general purpose diode will work just fine. The "Diode, Multipurpose" part name is a hint there.

 

Fuse 16 on the fuse box inside the truck powers the OBD port. The network is connected to the PCM and it may not work without power to the PCM.

 

I can pull that diode when back home from lunch, see if my OBD port runs. Give me about an hour

 

OBD port works without diode, PCM and IDM relays are OPEN Without it

Owe me beer 01/92 diode runs it too

PM me bub, I have a spare for you

 

your inbox is full. my battery cable is to the left side of the relay, then the starter is on the right side then runs to the starter

 

When you say works, you mean you can read data from your OBD2 port without the diode?

I would DM, but I need a couple more posts before I'm allowed to by the fourm.

 

Whoops on the PM box!

OBD2 port had power without the Diode, it would not pull any info as the PCM was not powered up. Jump those two relays and see if the truck starts. Or use a jumper with a fuse for the diode slot until you get my spare.

 

Thanks for checking that. If I'm ever in N. TX, I would be happy to grab a beer with you, on me. Reading circuit diagrams is useful to a point. I really needed someone to pull their own diode to tell me if that would actually cause my issue.