Let me start out by saying that I have exhausted every option that I have read on every thread that I could find on the internet regarding my son's 2002 7.3L not starting. What I have is no 12v power to the starter solenoid at the starter when I crank the key. What we have done so far, had the starter and both batteries tested, all good. Swapped out the starter motor fuse and the starter relay. Tried a new ignition switch and a new trans position sensor. Found major corrosion in the fusible link junction box on the drivers inner fender so we cut out the fusible links and put in a temporary jumper wire, still no crank. I have power to the dash, power on the power cable at the starter. I can jump the terminals on the starter and the starter engages. I found the shifter linkage bolts loose under the dash and tightened them up also. We have been struggling with this for 3 days, out in the lovely Michigan weather, since it couldn't have died in his parking spot in our heated shop, and I am completely frustrated. Are we overlooking something glaringly obvious? Any help is much appreciated. Thanks in advance. Jim

 

Also, on this wiring schematic for the 2002 7.3L, I have no fuses labeled 51 and 61 in my fuse box under the steering wheel. Is this drawing inaccurate or am I missing something? Thanks again. Jim

 

Here is a wiring diagram that might be more appropriate to your system:
http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=29299

If you get a error message about exceeding downloads when you select the link, just keep trying. I get the error sometimes.

If you pull the starter relay, first check that you are getting 12v where pin 30 of the relay would plug into the CJB. It should be 12v at all times.

If you are getting 12v to 30, then use a jumper wire to jump from pin 30 to pin 87. If this does not engage the starter, then you have a problem with the basic wiring. If this does engage the starter, then you can start looking at the relay control circuit.

 

Erik, Thanks for the reply. I will try this tomorrow when I go back to the truck. Also, your diagram also has fuse 61, it's actually labeled F2.61 in your diagram. Any idea if this fuse actually exists and if so where is it located? Thanks, Jim

 

It is part of the central junction box (fancy name for fuse box under dash)

Here is another diagram of the cjb and fuse numbering.

http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=73228

 

Erik, thanks again. This fuse panel legend seems to differ from the one I was using. Now I know what fuses are being referenced in the wiring diagrams. Jim

 

This is what you can do real fast. Take out the starter relay and check for voltage at the 4 pins in the cjb that the relay would plug into. Check for these conditions.

Key off: 1 of the 4 pins should be +12v (relay pin #30). If no voltage, than your problem is f2.61, fusible link, or wiring to the battery.

Key in run or start & trans in P or N: 2 of 4 pins should be +12V (relay pin 30 & 86). If no 12v on 86 than problem is f2.45 or trans selector switch, or associated wiring.

Pin 87 should show connection to the starter solenoid.

Pin 85 should be open (unless in start position) The wiring diagram shows this pin to be grounded, but it is the control lead that the pcm grounds to close the solenoid only when commanding starter to engage.

When relay closes, it connects +12v from f2.61 (pin 30) to pin 87 applying +12v to starter solenoid.

If the relay isn't closing, but you are getting +12v to pin 86, then you are not getting the control ground on pin 85 from the pcm.

From this, you should be able to pinpoint what circuit the issue is in.

 

Problem resolved. It ended up being a bad trans position sensor combined with blown fuse f2.61 that didn't appear blown but measured bad with an ohm meter. Thanks for the help Erik. Jim

 

I am happy you worked it out so your son has his ride back.

 

Believe me, my son is very happy to have his ride back. I'm just disappointed that it took me so long to diagnose the problem. But it is finally fixed.

 

Don't be disappointed and just think about all the money you saved by fixing it yourself.

 

I couldn't tell you the last time I took a vehicle to a garage for repairs. We always fix them at home. Just takes longer than expected sometimes, which is the frustrating part. But as you said, it does save a ton of cash and gives satisfaction in doing it ourselves. Thanks again for the help. It was greatly appreciated. Jim

 

I'm having problem with this one exactly. I get exactly .1v on 86 while in start. Fuse f2.45 is fine, my trans selector switch also seems to be fine but isnt getting power due to the DG wire from my ignition switch not getting power from my CJB. Any ideas why this could be?