PCM Power fuse

Truck was running great, just died all of a sudden. Cranked but no start. I immediately thought fuel pump as it it has over 150k on it. Got it towed home, and as I thought no fuel pump sound as I turned the key. Hoped it was something simple like a fuse, and I was right. But it is FAR from simple. It's the big fuse in the power distribution box. The one that according to my manual, is "PCM POWER". It's a 30amp and I had a spare so I put it in. Cranked, no start checked it and it was blown again. Any ideas any one?

Just noticed that the ground strap from the firewall is missing. I think it used to go from the firewall to the engine some where. Any one know 1)where it goes to; 2) If that could cause the problem? It's been running w/ out it since I put the engine back in. Now has over 500 miles on it so I doubt that the missing strap would cause it. Also, yesterday was super hot here in NJ. Could the heat have caused something. It just all seems so random for that fuse to just blow. And then blow again immediately. Maybe something was loose for a while, and then just gave, causing it to ground out/ short. Thanx for any help!

is it missing or "evaporated" as in "too much current". I would suggest you replace it as a start since currents tend to want to find other routes if they can go the way they want. How do you know its missing if its not there?????? Don't you have to know where it should be then????

No, no. I was reading some threads and more than once the topic of the ground straps came up. I didn't remember putting that one back (I just did an engine rebuild) when I put the engine back in. Went to check and sure enough, the extension piece for the body lift that I installed years ago is there, but from the extension to the engine, the strap itself is not there. I never put it back. I now have to go back thru my garage and see if it's even in there some where in the mess. If I find it, or when I get a new one, I need to know where exactly on the engine it goes. Thanx again, budwich!

Ok... that helps.... I guess. Not sure though as "strapping" isn't really well laid out in the truck CD.... basically Gxxx connection goes "here" but it doesn't show the "from here to there" type picture.... so that would seemed to indicate more of a "circuit ground" as opposed to what I would call "ground strapping" which I consider "braided copper". Anyways, as indicated it is going to be tough, it is most likely you have a "bare wire" problem somewhere. Not sure how much money in fusing you want to spend (cause I know fuse are "expensive" if you use them like "candy"), but if you want, I would try a "one time test" of replacing the fuse and just turning your key on. If the fuse doesn't blow then you quickly narrowed things down. If it blows then you are going to have to unplug stuff and do the resistance measurement thing (to save fuses) til you find the culprit. IIRC, some people in the past have found problems in the bottom of the PDB / FDB with wiring / termination points so you want to check there first. In addition, measuring resistance on 12v circuit that is rated for 30 amps is hard because that means the resistance could be .5 ohms or less and still be correct.... most "home" instruments are not calibrated that well to see / find that (ie. to see that versus a short).

I did find something about the PCM relay. If it were bad, it'd trip the PCM power fuse? If this is the case, I'll replace the relay, replace the fuse, and give it a try. What would cause a relay to fail? Time, heat, wear and tear, I'd imagine. So I'll spend the money on those two things, plus a few extra fuses, and if that ain't it, I'll have to go a bit further. Thanx again!

And by the way, yes, it's strapping, the un-insulated, flat, braided copper stuff.

It is unlikely that the PCM relay is the cause of the problem... its there to help things like this. Anyways, the relay can be check with a meter to see IF the contacts are shorting somewhere internally (ie. broken relay spring contact). Anyways, as suggested, try the "key on" only test as this eliminates the starter stuff which might have bad wires. It still more likely you have a "bared" wire touching somewhere.

Engine grounding strap on the SOHC, not sure if its the same for the OHV.
But on mine, its attached to a bolt at the top corner of the passenger-side head and the other side (which is not attached in the image below) should be bolted to the front of the firewall.

yep... looked at my 96, the strap is bolts just beside the wiper motor (top center of the firewall)... can't see where the other end goes but the previous post is probably good. Having said that, I doubt that you will be able to get at it with "convolusions of snake arms"...

IZ, it's nice to have your truck in such a state of dis-assembly! I've been following the build up! But that pic helps a lot. I think my other end attaches to a little hole on a bracket on the intake tho. I'm sure any solid ground point on the engine would be fine, just need to make sure it's easy enough to get to!

Bud, thanks again for your assistance! How can I check a relay? And the key on, but not start, if the fuse is NOT blown, I would have narrowed the cause to the starter, correct? If it only blows when I crank, then that'll make things a bit easier.

Yep.... takes out a lot of circuitry as the start circuit is pretty limited. As for relay testing, measure across the pins... don't have a drawing in front of me but for most of fords relays, pins 1 and 2 are typically the coil / pull up windings while 3,4, and 5 (3-4, 3-5) are the make / break contacts / switched connections.

I haven't decided to waste a fuse yet. Was thinking that if the truck just died on the road, while running, that what ever caused the fuse to trip was NOT starter related. I guess I should just waste a fuse to make sure, but if that's the case, and it's not the starter, where do I start looking for shorts. Or in other words, what wires come off the PCM fuse, and what do they supply power to? Thanx much,

"thousands"... you need a schematic. Go to autozone and look at their electrical diagrams.

So it went to my mechanic. I just couldn't find any thing wrong! Guess what he did. He took off the power dist box from it's mounting bracket, looked around, found nothing but when he put it back on, the truck started. He's so NOT confident that any problem was found, but he's been driving it around for a few days (I had him do some other things for me while it was there) and each trip has gotten longer and longer. No blown fuse yet. He's not charging for his "miracle cure" but says I'd better keep my eyes and ears open! I guess so! Well, at least my dipstick problems (I messed them both up during the engine removal) are cured, and my ground strap is back, and I have those shock mount skid plates that have been sitting in the garage for a year, installed! Hope to see y'all on the trails soon!

JR

Back on the trails!

Had the XLT back on the trails today. Just a little run, but man! I haven't really used it since doing the gears and locker (in the front, and Aussie locker). Right after the gears, the engine blew, and since having that done, I've been babying it. So it went into the woods today, and man, what a difference that locker makes. I mean, I only had to use 4wd twice, but they were both in some weird situations, and that front locker just worked wonders. Here's some pics

So I take it you're going to Rausch Creek sometime?

I have to! What about Paragon? Did I hear that the former owners got a new piece of property to use for O.H.V.'s?

jwrezz said:

Truck was running great, just died all of a sudden. Cranked but no start. I immediately thought fuel pump as it it has over 150k on it. Got it towed home, and as I thought no fuel pump sound as I turned the key. Hoped it was something simple like a fuse, and I was right. But it is FAR from simple. It's the big fuse in the power distribution box. The one that according to my manual, is "PCM POWER". It's a 30amp and I had a spare so I put it in. Cranked, no start checked it and it was blown again. Any ideas any one?

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Please i same problem help

rabiuquad said:

Please i same problem help

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Did ya see my "pseudo fix" in post 15 above? I've not had a problem since.