Hi, ya'll. I posted a thread on Sunday, 9/28/08 about my 1996 F350 psd not starting, indicating it repeatedly blows a particular fuse. I had some helpful responses in diagnosing the problem, but now I can't locate the original post. Someone, and I'm sorry, but I don't remember who, asked if the particular fuse was number 22, and it is. I disconnected what I believed to be the fuel heater element located on the drivers side of the fuel filter bowl, as recommended, and tried to crank the truck, and it blew fuse #22 again. The connector I disconnected is the second up from the bottom. The responder mention three, but I only see two on the side of the filter bowl, with a third located in the fuel line assembly itself. Did I disconnect the wrong one?
Also, let me apologize for not getting back to you who responded, but I had to work overtime, and help with the kid's homework yesterday, and just got another chance to get back to the truck today. Thanks again for all your help.

 

 

It's a 1996, Action4478, and thanks for the reply. BTW, we've already ruled out the PCM. Diagnostic computer reads "no data" from the PCM. But, that's before we discovered the fuse issue.

 

Thanks for the pic. I had the correct connector disconnected, but no success so far. Any other ideas would be helpful. I'm beginning to wish I still had my old 86 F350 with the 90 model 7.3 IDI I put in it. If only it were a crew cab, I would. But alas, hind sight is 20-20.

 

If you unhooked the right connector the only other two things on that fuse are the PCM and GP relay. Unhook the red/light green wire off the relay. it will be one of the small wires. Also it could be a wiring issue between the fuse and the heater, relay or PCM.

 

check for a chaffed wire in the main harness that runs across the left valve cover under neath the air intake.

 

Thanks, guys. I will try your suggestions when I get in from work this afternoon. Cross your fingers for me. I'm hoping it will be something simple, but I'm starting to think it may be a wire bare somewhere. I'll let you know how it turns out.

 

Look closely at the two wires in the IPR itself...

 

Here's the original thread: https://www.ford-trucks.com/forums/7...-starting.html

 

Sorry for taking so long to get back, and thanks cookie88 for locating that original thread. We've tested everything we could think of and out of desperation tried a 50 amp fuse in the number 22 location. The truck fired right up. If we are correct, the problem has to be upstream from the fuse block. If it were a direct short, even the 50 amp fuse would have blown, wouldn't you think? Anyway, does anyone have any ideas on the possiblities of the increase in amperage draw on the start/run circuit? If so, please let me know. I remember the old days when aluminum foil or a gum wrapper would be used to replace a fuse that contiued to blow, but I would rather not put a band aid on this wound. I would rather trace down the source and repair it properly, but need your help in coming up with the possiblities. My volt meter is at work, so I can't tell you exactly how many amps it is drawing. Any and all suggestions are welcome and appreciated.

Thanks

 

Click on Action4478's picture in post #2 above to enlarge it.
Did you disconnect the fuel heater?

1. 50 Amp...not a good idea..almost double the possibility of a melt down/fire!
Replace it with a 30A and try the following

2. Direct Short? Not necessarily,
A fuse is nothing more than the smallest diameter wire in an electrical circuit.
When you increase the size of the fuse (wire) the other wires in the circuit begin to heat up or burn.
Ever hear of a toaster element?

3. The fuel line heater is usually the cause of #22 fuse blowing. It protects the GPR, PCM
and, optional, 200A voltage generator/regulator circuit too. That's it.
Disconnect the small BK/O wire on the GPR. Start it. If the 30A fuse doesn't blow, the GP system has a short.
I doubt the PCM is the cause, it still runs.

4. Your volt meter might not be able to measure the very high Amp draw created by the Starter, GPR ect.
You will need an Amp probe or something that can handle up to 6-700 Amps or higher to do an AMP draw test.

Check all the connections in the starter circuit. This includes the grounds too. There a many.
Look for loose connections on the starter. The offending connection may or may not look like it's gotten hot at some point.
It may be the starter itself.

Does it roll over fast..look at the tach. Should be 300 RPM

 

Thanks for the reply, Cuda_jim. So far I've disconnected the GPR and fuel heater independently. Before we got this far into the problem, we even tried new PCM and IDM. The 30 Amp fuses are blowing as soon as the switch is turned on, before any cranking begins. The starter is fairly new (about a year old) and turns over very well. I replaced the original with a gear reduction (Denzo)type. That has been the frustrating part is this issue, we've eleminated all the obvious possiblilities. I have not looked for loose connections in the starter area, but will at first opportunity. Will continue to try to trace the weak link in the system. I hadn't planned to continue to use the 50 Amp in place of the 30 for long, just long enough to resolve this problem. Thanks again for your ideas. If you come up with others, please post them.