I recently acquired a '96 f-250 7.3PS,and it being my first diesel,just trying to troubleshoot is giving me fits.I've got a no-start problem that I believe is glow plug related.
Engine won't start,and the WTS indicator is out.I read the GP thread,and went at the easiest fixes first.

I checked fuse# 22,and sure enough,it was blown,however replacing it didn't solve anything.Next,I tested the gp relay,and it too proved to be faulty.Once again,replacement didn't bring relief.As I contemplated gp replacement(As far as I'm concerned,if I have to take a valve cover off,I'm not testing squat,I'm replacing everything.),I decided to go for error codes.I couldn,t get the reader to link with the truck's comp.OK,this is my first time trying to use one,but I'm fairly tech savvy,and the instructions were straight forward enough,so I'm thinking(DANGER!) that maybe the pcm is bad.

Does this seem reasonable?

 

i would tend to look in different areas before just jumping to a bad pcm theory. rarely do they go bad.

 

What kind of code reader are you using? Not just any reader will work with these trucks. I have one that works fine with my work truck (96 Dodge) but will not read the Ford..

 

Is the wait to start light working now that you changed the fuse

 

Just for giggles, check the cigarrette lighter fuse in the cab and the pcm relay under the hood in the dist. box. Also make sure that fuse 22 hasn't blown already.

 

OK,here goes:

1)The scanner is an Innova 3100e Can OBD2 diagnostic tool

2)Fuse 22 is still ok

3) Cigarette lighter fuse(#16) is ok.I've re-checked all fuses in both locations,and they check out fine.

4)The WTS lamp is still not functioning

5)I swapped relay 1 with relay 2(horn,same part numbers),got no relief,then re-swapped to original positions.


Does the circuit the WTS lamp is on stop at the gp relay,or will faulty gp's or a break in the wiring from the gpr to the gp's cut it out?

 

Normally if your not getting a wts light and have changed all the relays and checked all the fuses it is pcm related.
Are you reading any rpm while cranking? If not try the cam position sensor. Then if its still not it could be pcm.

If you know anyone with a snapon or auto enguinity scan tools try those.

Is it tuned?

 

There's no rpm reading when cranking.I'll check on the cam pos. sensor.It'll be a little later,had snow last night and truck is outside.

 

How do I test the pcm to find out if it is definitively it?

 

Is the truck completely stock? Or does it have a TS chip? Every once in a while my TS will make my wait to start light not turn on and it will blow fuses. If I unplug the chip and clean all the terminals its all good again. Or even just unplug it it will start for that matter.

 

If the PCM isn't receiving power, which it seems it is not since you have no WTS light, it doesn't matter what scanner you use, it won't communicate with the PCM because it isn't turned on. I would take a look at the PCM connector in the driver side wheel well if it were me. Make sure the 10mm bolt is tight for starters, unless it was loose and starts right up after you tighten it, loosen the bolt and unhook the connector for inspection. It's possible, although unlikely that the connector is corroded and not making a good connection.

As far as the relays go, I would try swapping Relay 3 into the place of relay 1. Relay 1 is the PCM, 2 is the IDM and 3 is the horn, so I would use the horn relay to test the other since it (the horn relay) can be easily tested to ensure it works.

Another assumption I am making is that when you turn the key to the run position you are indeed getting other warning lamps on the dash?

If this assumption is correct, and you're getting other lamps lighting, I would try testing the GPR with a test light. When the engine is cold and the key is turned to the run position, if the PCM is working the relay should kick in and there should be power to BOTH the big terminals. This test is just in case, by an off chance the WTS light bulb is burned out.

Also I'm assuming that while cranking in this no start condition, there is no smoke out the tailpipe?