1992 E40D blues. Works with jumper.

[Wise Mule]

1992 F-250 XLT, extended cab, rwd, 7.3IDI with E40D blues. I recently purchased this truck from Oregon with 103k. Seller was less than honest about condition. However it is a Beautiful truck, well worth bringing up to speed, excellent condition, except....
1) Low voltage. Solved. Found that someone had replaced the 1G alternator and over torqued the B+ post and partially shorting out internally. 5 year old batteries. Replaced with same for now, 3G conversion later.
2) Glow plug relay clicking. Solved. Found after market glow plugs had incorrect resistance. Replaced with OEM. After market relay module improperly wired. Replaced with OEM.
3) Trans in limp mode, OD light on dim, no tach. Unsolved. This is what I have eliminated thus far:
A) PSOM temporarily replaced with a used unit from my ‘93. Good.
B) Trouble shooting TPS, MAP, TECA(TCM), Relays etc... found .39 volts
supply. Manually jumpered relay and 5 volts. System seems functional
at this time with jumper. All fuses and relays check good.
C) Full power and grounds throughout so far. Relay has full power and
ground but signal to relay with key on engine off is .8volts.

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This truck has the newer relay/fuse box with lid and 5 relays. Also noted is Ford reman transmission and TECA. Not sure where to look from here. I believe that there is insufficient power coming from the ignition on.

Question- Does the power signal to the relay simply come from the ignition switch?

There are other. I believe non related issues I’m plowing through such as:
1) Hard power steering.
2) Small leak in radiator.
3) Drivers side window regulator.
4) A couple of injectors dropping out at idle.
5) Turn signals going into AFIB.
6) Touchy brakes(if you hit the pedal more than easy the truck will stop so fast
the paint might fly off).

 

[Black dawg]

Probably get some responses if not posted in the tech articles section?

I vaguely remember a fuse being between the ignition and that relay.

 

[snicklas]

Moved to IDI section

 

[Booyah45828]

Prodemand says that relay coil gets ign+ from the switch, through fuse U(20A). That fuse also powers the fuel heater as well.

So check fuse U under the hood and see what volts are there. If it's blown, I'd suspect a shorted fuel heater. If not, check for voltage at the fuse. If it's low at the fuse, ignition switch might be faulty, check voltage at switch and fuse P, which powers the switch. If voltage at fuse U is good, wiring diagram says there is a diode in the wire between relay and fuse.

 

[Wise Mule]

Thank you for the help in moving my post in a better area and the new info.
I will start at the switch as I have already worked the engine compartment wiring and relays. Again what I have found so far is low power with ignition on to the relay signal wire. A schematic of the ignition switch and color code would be helpful. I noticed two black plastic modules under the dash above the steering column and was wondering if the ignition circuit ran through one or both of those.
Good news is that I found out why I could not read codes. The sales guy in Oregon told me that “There is no engine light or anything“.
Another dishonesty or actual truth? I pulled the dash again and in a way he was right, the light bulb was missing!

 

[Booyah45828]

Low power with ignition on to the relay signal wire. That wire passes through fuse U, so start at fuse U, key on engine off, check for 12v. If you don't have it, then go to checking the switch. If you have power at fuse U, check continuity between fuse and relay, as there is a diode that might be open.

I can't save and upload the wiring diagram. I'd have to print, then find someone with a scanner, and then upload. I'm sure it available on the internet or paper somewhere.

 

[Wise Mule]

Thank you for the guidance. After tracing back from the relay, I found a partially blown fuse 22(engine bay, fuel heater/glow plug relay module/TCM). The fuse initially checked good by probing the top contacts. Someone had cut the wire and connector off at the fuel heater and had spliced a generic wire with an open spade connector. They also had cut the wire to the fuel vacuum/filter restriction sensor and reconnected it. I checked the the fuel heater element separately and found it bad. The connections were very poor.
Reading up on that fuse position, I found information that puts that fuse at 20amp for a gasoline engine and 30amp for diesel. I had found a 20amp fuse there, I replaced it with a 30amp. I am ordering a new fuel heating element and was thinking about adding an inline 20amp fuse near the fuel filter housing to help protect the TCM. It would be nice to separate the power supply to the TCM, but for now it seems easier to just add a lower fuse at the fuel heater.

 

[franklin2]

Good news is that I found out why I could not read codes. The sales guy in Oregon told me that “There is no engine light or anything“.
Another dishonesty or actual truth? I pulled the dash again and in a way he was right, the light bulb was missing!

I have never messed with one of these "transmission only" ECM's, but it is my understanding they are just a EECIV computer just like the older fuel injection cars and trucks, just with less features. The very first EECIV systems did not have a check engine light, but they still had codes and you could read them. See if you have these connectors under the hood somewhere.

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If you find those connectors, you can pull codes. Here's how to do it with a testlight or old voltmeter with a needle.

EEC IV Self Test – Ford Fuel Injection and EEC IV Electronic Engine Control – EEC 4 – TroubleCodes.net

www.troublecodes.net

 

[Booyah45828]

Thank you for the guidance. After tracing back from the relay, I found a partially blown fuse 22(engine bay, fuel heater/glow plug relay module/TCM). The fuse initially checked good by probing the top contacts. Someone had cut the wire and connector off at the fuel heater and had spliced a generic wire with an open spade connector. They also had cut the wire to the fuel vacuum/filter restriction sensor and reconnected it. I checked the the fuel heater element separately and found it bad. The connections were very poor.
Reading up on that fuse position, I found information that puts that fuse at 20amp for a gasoline engine and 30amp for diesel. I had found a 20amp fuse there, I replaced it with a 30amp. I am ordering a new fuel heating element and was thinking about adding an inline 20amp fuse near the fuel filter housing to help protect the TCM. It would be nice to separate the power supply to the TCM, but for now it seems easier to just add a lower fuse at the fuel heater.

20 amp with the gas or IDI. 30 amp with the powerstroke, according to prodemand wiring diagram. Prodemand wiring diagram still references the underhood fusebox with letters up to 94. On the other hand, they have a separate diagram where they show the diesel fuse box, and it has numbers, with number 22 in the same location as fuse U, So I assume fuse U= fuse 22. Gas fuse box still shows letters, so I'm not sure when that change happened.

I see no issue putting the 30 amp in there, and then putting the fuel heater on it's own 20 amp fuse in the wire harness. But I wouldn't bother with replacing the fuel heater, as I don't believe it's all that useful IMO and is a common source of leaks/air intrusion. I'd be sure to get the fuel vacuum sensor operating, as that's your warning if the fuel has water in it, and also if your lift pump has failed or isn't up to par.

 

[Black dawg]

Partially blown fuses are interesting, but I dont think I have seen them on any circuit other than ones powering fuel heaters? Was actually my first thought when you found low voltage in that circuit. Saw one on a superduty powerstroke recently.

 

[Wise Mule]

Production date of this truck is 11/91. I also have the same (Now parts donor)truck production date 8/92. Both have the newer engine compartment fuse block that supposedly is 94-97. Here is a picture of the partially blown fuse(on the right). I’m in the marine industry, trying to slow down but like most fields the younger group is almost non existent.

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When faced with a problem, I most always go back the basics. The ABC’s, process of elimination. Here is case where I missed this the first pass on the fuse. Now looking deeper into this circuit, with support and guidance from this group, I came to the conclusion that a 20 amp fuse is correct for position 22/U and eliminate the fuel heater. My reasons are simple:
1) I do not live in polar bear country.
2) The heating element is of minimum function and problematic.
3) I will be adding a WVO system with an separate inline fuel heater.

 

[Wise Mule]

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This gives my age away... I remember buying this new off the tool truck.

 

[IDIBRONCO]

This gives my age away... I remember buying this new off the tool truck.

Wow. I do know what it's for, but I've never seen one.

 

[Wise Mule]

it is/was called a “Winky Blinky” it has the basic diagnostic jumper configuration for AMC, GM and Ford. Dodge had the “turn the ignition 3 cycles“ and read the check engine light flash sequence. Basically a pocket code reader.