I have read through so many forums about this issue from fuel pump not working to starter staying engaged after cranking but most advice is to just keep replacing parts. Not bad advice but I'm determined to get to the cause and not just fix all the symptoms. I'm praying someone has discovered the fundamental flaw in this design and can save me more headaches, but if not I will persevere...

Here is the long troubleshooting history...

Truck runs great not a thing wrong, the air conditioning even works! Start out on a rainy day (truck is kept in a garage but an unusual circumstance left it outside for the day), cranks and starts fine, 100 yards away it burbs, like it completely missed for a split second, then back to normal. 10 miles away, it shuts down instantly.

Open the hood, smell the dreaded electrical burn odor but see nothing wrong. I go to start it, and she cranks but doesn't start. Try a few times and then she keeps cranking even with the key out of the ignition until starter dies.

Tow home and start the troubleshooting.

Replace starter, cheap new fender starter relay breaks while installing so I use the old one (original). Sure enough she cranks but doesn't start.

Move on to spark, fuel, air....I'll be brief here but finally determine ground from ECM is not being applied to fuel relay. Great trouble shooting tip, you can provide this ground through the test connector to determine if your fuel pumps are operational, and test pressure on fuel rail. Truck still would not start which led me to knowing the fuel injectors were not operating. Moving on...

Reluctantly, pull ECM. Can't find exact part match so I crack it open. Inside there is hole burnt through the PCB(electronic board) under a diode connected to the power pins (37 & 57 I believe) and a disintegrated trace from these pins on the board. Hole/diode lead is about midway in the burnt trace and there is a ground screw (holding the board) close by that shows arc mark signs. Observation - noticed slight water deposit marks (mineral deposits no water) around connector and this part of the board would be the lowest point.

Aha, I got it water shorted the diode lead to the ground screw. That was the problem, well sort of. I repaired the board by replacing the trace with a wire and even replaced the electrolitic capacitors on the board (yes they had spewed a long time ago and one is right next to the diode. Diode was still good believe it or not (Couldn't find the specs for the part number 12S44 motorola but appears to be a 3 amp standard diode).

Put the ECM in and walahh, cranks and starts on the first turn (charged battery while I was doing all this). Take ECM back out, conformal coat it, tape all the wires back up going to the ECM (checked to make sure nothing was burnt immediately upstream of the connector). Put everything back together and shes running like a top. Drive her out and back for a 10 mile trip to relearn all the ECM internal calibrations. Perform key on and running self diagnostics and get only one code. 33 EGR valve movement not detected. Figure I can check this out later because right now I am the man and need to pat myself on the back.

Go out next day and she cranks right up, but sounds odd and starts to have a high RPM idle. This probably only lasted a minute and she instantly stops. No crank, starter is dead. I believe the starter was still engaged and this lead to the ECM kicking up the RPMS. Not sure why it died unless the Back EMF from the started killed something.

I know the trace I replaced did not blow again because the fuel pumps do come on when I turn the key to run.

Now the check engine light does not go off (in run) now so I can't do the key on diagnostic.

Before I go and get another starter and new solenoid, I did some additional checking on the starter solenoid. It functions correctly (just used a jumper from the battery post instead of the signal wire) I hear the relay engage and disengage. I checked the signal wire and in run it has 7.3 volts! Looked at this circuit closer and realized it is tied to the ECM. Getting late, I will continue my story tomorrow...

 

The sticking starter relay is caused by the battery voltage going too low. When the voltage drops the current goes up and then you will get burned up starters and starter relays.

The wire on the starter relay does not go to the ECM. It goes to the ICM mounted on the side of the distributor.

The signal wire as you call it to engage the starter relay more than likely will not light a loading test light and the 7.3 volts is a ghost voltage. That is why I do not like using a meter in these circuits for troubleshooting as they will lie to you.
Meters are good for checking the charging and state of charge in a battery and a few other things but not for tracing problems in the starter and fuel systems.

Your whole problem was caused by the dielectric grease that had dried up in the ECM plug and let the water in when it rained. We see this a lot when someone washes the engine compartment and then ECM burns up. The dielectric grease should be reinstalled in the ECM plug about ever 10 years to prevent this from happening.

 

Thanks subford! Checked the current and that 7 volts only provides 20 mA. I had unhooked the ICM connector and saw that this voltage became 11.5 volts and thought I had a short somewhere. I thought one possible cause could be power coming from the ECM through the ICM as they are connected. I believe there is a connection back to the ECM (pin 30) at the clutch switch also. The schematics seemed to indicate this connection is made at the same time the starter circuit is closed by the clutch. I still have no clue why these connections are in the starter circuit. I was headed towards a lot of wiring trouble shooting including the ignition switch. Also I will be sure to pick up some dielectric grease. I noticed the wiring is such that any water would run straight down to the ECM connector.

So I will go get a new starter and relay. I will have the battery checked and replaced if needed. Although the battery is old, I didn't suspect it, as it seems to hold a charge and has been powering everything fine through the troubleshooting. I've seen a lot of posts that suggest replacing the positive cable with a larger cable to correct this problem, but that would just be a different way of getting higher voltage for a little while.

Thanks again, it's apparent that you know your Fords. I'll get a chance to make this all happen on Friday, and I'm hoping I have that great running truck back, I'll be sure to post the results.

I'm also assuming the check engine light is locked on until it is cleared by actually starting (I guess I'll find out when I remove the battery since this should clear any codes).

 

When I said that the lower voltage (from prolong cranking) would up the current going through the starter relay contacts I was not saying the battery was bad but just that is what happens when you run the battery down.

Pin #30 just tells the computer that the engine is cranking by way of the ignition switch.
I think the computer then operates the IAC valve with this information.



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Did this ever get fixed?