hey everyone, i appreciate any help i get here. heres the deal. the first time this happened i came out of the gas station to start the truck back up and it cranked for a sec or two but didnt fire. then f102 popped. the wierd part is that the radio and instruments still worked but slowly faded out. replaced the fuse and it started right up and ran long enough to get home. i turned it off and restarted it to see if it was a freak incident or what. blew again. I replaced the starter/solenoid as a first attempt....didnt fix it. then started tracing wires and found nothing. I can hear the starter relay clicking when turning the key but no starter action and still blowing the fuse. gonna go broke trying to pinpoint this any help would be awesome. thanks

 

What was the order from cranking to blown fuse ?
- the starter over for a second or two, did you then let off the key after this to stop the starter action ?

The instruments and radio still worked then faded out. What do you mean by this ?

You replaced the starter and what solenoid ?

What modifications are done to the truck ?
- remote start, AMP, headunit, etc.

Are you the 1st owner, and know the complete history ?

 

no i didnt let off the key, once that fuse blows it takes out the power for the ignition system which i'm sure you know. as far as the instruments and radio i'm talking about the lights. when it first blew they were full brightness and then prolly 10 seconds later completely gone, but it wasnt immediate you could see them dimming. the starter solenoid is what i replaced with the starter instead of just getting a new solenoid. figured i'd get a lifetime warranty while i was at it. only mods to it is that its been lifted since new. has a factory sub in it under the drivers side rear seat. and yes the only owner. appreciate your time. I took an ohmmeter to both sides of the f102 prongs in the fuse box to ground tonight while a buddy went through all the key positions and the only time it rang out was when it was in start position on what i would call the "load side" of the fuse. going to pickup a new ignition switch after work tomorrow and see if that does anything.

thanks

 

Sounds like you may have found something, shorting to ground in the "start" position? Have you checked the Starter Relay in the Junction Box? Also, it looks like F102 also goes to the Digital Transmission Range sensor.

 

Ok, lift could point to a harness issues going to the DTR ( SWAG ).

the lights dimming, is this the same as when they shut off ( interior fade to off function ) ?

as Jetpilot2 pointed out, this goes to the DTR, which in the case of starting is the "neutral" switch function ( the truck only starts in Park or Neutral ).

Start by doing a physical check of the wiring to the DTR ( driver's side of trans ) to make sure the wiring does not have any chaffing on it, where it can momentarily ground itself to the trans or frame and blow the fuse.
This is a big SWAG, but could explain how some times it works fine, other it blows the fuse.

Unplug the DTR and unhook the harness so you can get a good look at it, might be very minor chaffing ( members' replies to blowing the fuse for the O2 sensors ).

I am going to say rather than an ignition switch, the next to check would be the DTR itself.
You can test this by pressing and holding the brake pedal, turn the key to the run position, move the trans to neutral and then turn to start. It uses the same circuit from the ign switch to the DTR, this is why I say only after doing a careful examination of the harness.

 

ok, so heres the latest. Jumpered between the hot(all the time) and hot(in start) wires in the ignition harness 250. blows the fuse, which tells me the ignition and cylinder are not my problem. then moved down to the harness on the dtr sensor and did the same thing. db-og wire to tn-rd wire. still blows, which tells me its not the dtr sensor. also tried the starting in neutral and it did the same thing.

the part that is throwing me off is that the starter relay doesn't pull in everytime you try to start it, but everytime that it does the fuse blows. to me that would tell me i have a bad starter relay, but i've bought 2 new ones and swapped out one of the other relays and they even blow it.

also i've read that the cop's and rfi cap's are the only other thing off 102 thats not fused and i unplugged all of those harnesses too to rule them out.

the only other component that i can see 102 going to is the wire off the control of the starter relay that goes to the pcm, however i have no idea on what to do with that if you can even try to trouble shoot it or anything. Can you pull the pcm out and take it somewhere to have it diagnosed?

besides all of that the only other thing that i can think is that its in the actual wires and i have rang through them for continuity and they all ring out. But in my thinking that doesnt necessarily mean that they arent shorted to ground and still ringing through.

just thought i'd throw all that off your heads and see if that brings any other issues up that i'm missing.

thanks

 

If you want to test if it is the starter motor relay or the connection to the PCM on the ground side, pull the relay and try jumpering it.

If the fuse blows, either it is DTR wiring to the starter motor relay, or one of the other items on the list.

The other thing, when you were jumpering the wires, did you unplug the connector at the DTR ?

The lift has me thinking it is wiring harness.

How did you test them ? ( you make note that you did, but no indication of how ).

 

Something is shorted to ground, instead of checking them for continuity from end to end, you need to check them to ground to narrow your search. Also, as Scully asked, how did you perform the test.

Scully, when you say remove the relay and "jump" it, which pins exactly? I'd be weary of jumping the PCM control to power and the other two are only going to turn the starter on F101. If I'm misunderstanding please let me know, I'm always willing to learn.

Forgot to mention and a very LONG shot, but F102 also goes to the instrument cluster in case everything else pans out.

 

Jetpilot2 thank you for asking the clarification.

NEVER jumper something to the PCM.
If the PCM is not performing that operation, another input the PCM is stopping the function ( i.e. this case, PATS has not completed, and ground is not applied to the starter motor relay by the PCM ).

I was talking about on the DTR, Dark Blue w/ Orange Stripe wire to Tan w/ Red stripe wire with the DTR unplugged.

This simulates the "neutral switch" with the DTR removed from the list of items ( checking if the DTR is causing an issue ).

I have seen blown fuses with the starter circuit be caused by the connector being crapped up, or in this case I do not get the warm and fuzzy with the harness considering the life ( supposition on my part, might be unwarranted attention )

 

Gotcha!

Yeah, I know about not "jumping" a PCM control, that's why I asked exactly what you were referring to.

Hopefully BigB will let us know what he finds.

 

Hey Big,

Did you ever get this resolved? We'd like to know what you found.

 

i had the same issue with my 2004 Ford F150. On my truck the issue was caused by some corrosion Relay #203 resulting in a poor connection.

 

Thank you for posting what your resolution was for the similar symptoms

the next member that is having a similar problem will be thankful for a push in the correct direction that yielded results.

BTW : Welcome to the site.

 

I hate to burst your bubble when you believe you're trying to be helpful, but there's absolutely no way that any fault with relay R203 can cause fuse F102 to blow on an 04 F150. There is no connection between those circuit components and they're at near opposite sides of the CJB.

 

Mr criticism on a harpoon, you might want to cool it. You have done similar.

2005 Owners Manual