i'm starting a new thread on this as i've hit a problem in restarting my project truck and hope to get the attention of any experts on the two expensive computer boxes on our trucks that may be out there.

in my engine rebuild thread, i've detailed what i've done and what hasn't worked, but i'll describe it briefly here as well. the details can be found here:
https://www.ford-trucks.com/forums/1...l#post14880691

So, i got my rebuild engine back on the frame, the radiator, AC evaporator, IC on the mounted rad support and the cab on the frame with the dash installed.

at this point, i was planning on starting the engine up to run it a few minutes and convince myself i had no leaks or other major problems before putting the fenders and everything else back on.

HOWEVER, after hooking up the batteries and grounds and all harnesses, when i turned the key to on, i got a rapid clicking from the IDM relay (like at least 10 clicks a second) and the PCM would not come on (no WTS light, and my Aeroforce Scangauge would not read anything). this has been followed by 5 days and about 12 total hours of troubleshooting to no avail.


in short, i've done the following:

- assuming it was bad grounds or power supply lowering the relay voltage, i checked and doublechecked everything. grounds are all 0.3 ohms or less to battery and voltage is 12.8V at all points in the fuse box.
- pulled the IDM relay and the PCM fires up just find and the AF interceptor reads parameters fine. only error codes are for Batteries disconnected and EBPV unplugged
- swapped fuses and relays from different circuits
- checked all IDM wiring for continuity to valve covers and for shorts to ground. all good.
- disconnected engine wire harness.
- tried all combos of spare PCM and IDM set i have.
- changed engine fuse box and wiring to spare one i had. still same clicking.
- pulled all fuses except IDM, PCM and instrument fuses. then pulled instrument cluster as well. still just clicking
- removed ignition switch and jumped power to "run" state. still just clicking
- disconnected big through-firewall connector and jumped power from yellow wire to red/lightgreen wire to power up PCM/IDM circuit. still just clicking.

also, of note, a few times the clicking has actually stopped after about 10 seconds and the PCM fires up OK. but when i try to start the engine here, the PCM goes out. this only happened a few times and i can't figure out why. its been a while since this happened, but next time it does, i will run a buzz test...

the few things i plan to do still are to ohm out all PCM pins to make sure there are no shorts to ground that aren't supposed to be there, but i'd be surprised if that was the problem on both harnesses.

aside from that, i'm just about at my wits end. i have replaced or removed literally every part of the system i can think of to no avail.

so, i appeal to you all for help!

a few specific questions i have are:
are there any specific situations that might cause the PCM to shut down the IDM immediately after it powers up, then try to restart it again? since the PCM just provides a ground for the IDM relay, it seems like its something intentional the PCM is doing, or a PCM internal circuit problem. if it was a low voltage problem causing the IDM relay contactors to open, i'd expect PCM relay to open as well - but its definitely not. however, the PCM does not stay on during this problem...

and i've read through this thread on parameters and what it takes to start the engine many times (https://www.ford-trucks.com/forums/1...l#post11315231), but is there anything similar out there for what might cause the PCM to shut itself down immediately? like a sensor short somewhere on the engine or something ...though it can't be that as it still has this problem with the engine harness unplugged. ...maybe if it doesnt see a certain sensor? ok, i'm talking to myself here now. this is a common theme these days.

assuming i can't figure this out soon, i think i will try just providing power directly to the IDM by a switch, instead of having the PCM provide the ground for the relay coil. this sounds dangerous, but i see no other options at this point.

i feel like there's something simple i'm missing here, but i just can't see it.

oh, and can anyone recommend a good place to send a PCM and IDM pair for testing?

please help!

 

Just had a thought - if there is a "keep alive memory loss" code, or whatever it's called, where does the PCM get power from when the key is not on? I dont remember seeing a circuit for that in my studying of the PCM pin outs.

I ask because I've been disconnecting and reconnecting the batteries like it's my job. When I reconnect them, I generally flip the key to run within a few seconds. I may try waiting a few mins next time in. Can't hurt. And I pray it were that simple!

Edit: Ok, there is a "keep alive power input" to the PCM... Can't hurt to leave it sit connected to the batteries a good few minutes or so. I'm desperate enough to try that.

 

I swear it sounds like a ground issue to me JP. On all the ground points around the rad support and the driver side fender, strip pieces of wire and put the bare wire under the bolts that hold the grounds and make it so the bare wire is touching the terminal ends on the ground wires directly. Run each one of those wires from every ground point straight to Negative on the battery and see what it does. Have you tried unhooking the two small wires from the GPR ?

 

Yep, small gp wires are off and big one is unhooked from the starter relay.

That's not a bad plan with the direct grounds bill. I ohm'd everything out back to battery negative, but since this is somewhat of a high frequency problem, the impedance may be higher under load. Worth a shot!

 

When I put my son's truck together back in the spring I wanted to start it before I had it all together. I didn't have the rad support on yet but I had the grounds hooked with alligator clips, then jumper cables, and then finally had to crimp terminals on pieces of wire and bolt them to all the ground wires and run them to the battery neg to get it to start.

 

well, i haven't done that exactly, so here's to trying.

actually, now that i think about, the battery terminals are the only things i haven't touched since this problem started. i know for sure i brushed and dielectric greased them all when putting them in, but haven't touched them since.

that's step number 1 of the daily frustration event tonight now!

 

I've had trouble with dielectric grease causing bad connections before.... its a long shot but id take some brake or carb clean and clean all that stuff off your connections at the batteries ect, and hook um back up and try it again before anything else.

 

I haven't had good luck either. I had to clean it up to use my Jumper cables.

 

A bad battery can cause this. Try unhooking one or the other to see if the clicking stops.

 

well, i'll be pissed and ecstatic at the same time if the dielectric grease is the culprit.

i do plan to try to one battery disconnected, then the other plan, though.

 

Any luck???

 

I won't get to the barnn till after the kids are asleep tonight. I'll post if I get it for sure, though!

 

Ok boys, good news - finally.

She's not running yet but I'm pretty darn sure I have found the source of my problems.

I'll post more tomorrow but in short, I took bills advice and ran a ground back from the rad support and fender grounds straight back to the battery. The clicking was still there but would stop after a few seconds and everything boots up then.

So I started jiggling the one single PCM ground that screws to the fender and got the chattering down even shorter. I then clipped the old dirty ring terminal there and soldered a new one on. Even SHORTER chattering.

With my ohmmeter in the coil ground terminal of the relay and the PCM on, resistance was 2.0 nominal at this point but I could get it down to 1.6 ohms with enough jiggling of that wire.

Soooo, I'll now clean all the pins in this circuit real good and try to get the resistance down even more. I'd likes to run a new thicker wire too but don't have the pin/socket tools and spares to do it. Anyone know of what type they are and where to get them?

Alternatively, anyone know of a relay that might be more tolerant of a few ohms in the ground circuit? I tried a sealed Hella brand one I had bought to run the fuel pump but that one was worse.

And Nate - I was going to call but lost track of time. Hopefully a bit more work and I'm up and running though!

 

Sounds like it's getting there! Hope you get it nipped in the bud!

 

Pulling for ya dude!!!! Hopes and prayers for reward for the hard work!!