. Have you thought about installing a manual switch to turn the glow plugs on and off?
That could eliminate a lot of problems for you and probably the easiest fix at this point.
I'm sorry, but I would provide you with the link to do this on the website. But I have a day's work of skid steer to do.
However if you send me an email I'll be more than happy to do it later this weekend.

 

Maybe the extra load with glow plugs is causing it to crack too slow?

How about sharing a photo of the GPR and wiring? Maybe someone will spot something in how it’s connected.

 

I'm with Jason on this one. The only thing I can think of is that the GPR firing the GP's brings the battery voltage down to a point that the PCM and starter are not happy with. Ford tells us 10.2v is the absolute lowest, but we usually say 10.5v to allow for human error and instrumentation quality variants. Do you have a multimeter or one you can borrow? You could have a helper attempt to start the truck while you put the probes of the multimeter on the passenger side battery and read the voltage while cranking the engine. Ideally, you would want to connect FORScan via a mobile device or laptop, but I believe you said your tablet was upset with you.


Below is a diagram I built indicating the wiring with colors taken from this post - https://www.ford-trucks.com/forums/1...l#post19719700 . Ignore the two "ground" connections at the 12 o'clock and 3 o'clock positions. The pink with white trace control wire in an OEM configuration is to be at the 12 o'clock position where I have the SPST switch.




Below are a couple of progress pictures I took when installing the SPST switch for the GPR activation.






For further reinforcement of what your eyes are telling you, see the pictures below.

 

Thanks for the help on this problem, yep I've got several multimeters from my days as a grease monkey. I tried it again this morning with the G Plugs disconnected and it lit up very quickly. I've checked battery drop when the glow plugs turn on, ~.7 volts, but neglected to check voltage while cranking, that could explain this. My truck has new batteries and is changing right on the money. The only weak spot are my battery cables which are 23 years old. As long as I'm spending money I might as well replace them, any suggestions for a source (I'm too lazy to make a set myself)?
I spent the night figuring out how to wire a separate switch and relay for the glow plugs if needed, I have an extra new GP relay from NAPA. After seeing Sous pictures, thanks again, it looks like I could install a momentary, normally off SPST switch on the ground side of the existing relay and only energize it when needed. That way the plugs would be off when I craned the vehicle. Will this setup compromise or hurt the PCM? I'll read Sous thread on his modification shortly, it may answer this question.
I'm beginning to see the light at the end of the tunnel, hope it's not a train wreck coming my way.

 

Years ago during my technical training, they would pound into our brain "your circuit is ONLY as good as the WEAKEST link". You can have the best batteries and starter in the world, but if the wires between them are not up to the task, the entire circuit is brought down to the substandard level.

Also, I lost all and complete faith in FLA batteries a few years ago. I got tired of the free replacement and/or prorated warranties. Those marketing gimmicks did not pay me back for the time lost swapping the battery out and the headache of dealing with a dead battery when starting the vehicle to head off to wherever it was I was going. I swapped ALL vehicles to AGM and even put a lithium battery in my John Deere riding mower that used to be in my motorcycle.

When you take readings of the voltage during a cranking and no start scenario, test both batteries at the terminals and then the starter relay as well. Make some notes about the readings and come back to us. Visually inspect the terminals on the batteries, starter and starter relay. Maybe perform a resistance test on the cables and wires between the batteries and the starter. Something will stand out and make you say "that ain't right..."

@FordTruckNoob bought a complete set of cables that he says are of high quality. I tested my OEM cables and they were good, but I upped the game by doubling up the cabling when I installed the high output alternator.

Yes, you are correct about the momentary SPST switch. Super easy to install if that is the route you want to take. I prefer this method and can always return the truck back to OEM in less than a minute if I need to. The SPST switch will NOT harm anything and definitely not the PCM. You are simply removing the ground leg of the circuit from the PCM where it is automatic based on the EOT and putting the ground leg of the circuit in control of you, the driver. Again, I prefer this method. Although, I prefer my ZF6 over the 4R100 and have walked to the beat of a different drum all of my life, so there is that.

Many years ago my wife and I were fortunate to meet you and your wife. We both recall that as a good day another benefit of being an FTE member. If you need any help, you have my number, just give me a shout.

 

It could be the cables themselves but most often it’s just a poor connection at the terminal. I’ve had it happen to me a couple times. One time I caught it while changing the batteries… those batteries went back to the store. The truck cranked fine after fixing the connection. 🤦‍♂️

They can start on 1 battery, or 1 with just a touch of help from the other but are not happy about it.

Sous said what I was thinking. My guess is the PCM is not seeing enough cranking voltage when the GPs are on to tell the PCM to fire up. You could test it with a meter. I would connect to the cables and not the battery as if the connection is poor it may not show what the PCM is seeing.

Good luck!

 

for me,
I prefer the Spring Loaded, normally off SPST switch....

forget to flip it back off, and burn up the glow plugs

 

This is what I did a decade ago. The ONLY function a glow plug is for is to help heat the combustion chamber enough to get the diesel fuel to ignite on a cold morning. After that they are off for the entire rest of the journey, long or short doesn't matter. Even on errands and stuff, the engine is still warmed up enough, you don't need them to heat up to get the engine going.
Yes, you'll get more smoke in the morning until the engine warms up, but for my truck it took all of 1/4 mile at most to completely clear up when I was still living in Seattle. Now I live in AZ and almost never have to bother with pushing the switch any more.

 

Yes, a momentary SPST switch as described above.

Dan, your advice and guidance was what led me to accomplishing this "mod" on my truck. After I found the PCM to be triggering the GPR on and off at a few second interval due to the high output alternator, I decided I wanted to take a different route.

 

My stock passenger side positive cable was corroded/eaten almost into. I purchased this hard start set from these guys. Good quality cables. And made a difference in how fast it turns over as well.

 

. I live in PA, and I have a momentary switch and led light I did on my truck and it's a no brainer.
. You can switch it back to stock rather quickly. It extends the life of your newly installed glow plugs. Allows user input when starting vehicle. And, I never activate my glow plugs in the Summer or when outside temp is over 50 degrees.
You can deactivate the glow plugs manually JUST BEFORE starting the truck to save extra battery voltage for the starter. The starter ( or connected cables), could also be your weak link or problem in starting issues.
. Curious to what your fix ends up to be.

 

My "fix" is that I've completely disabled computer control of the glow plug system in favor of the momentary push-button switch on the ground circuit of the glow plug relay. Glow plug only are heated at my command. The other mod that I did was to disconnect the small power wire from the small positive connection that powers the relay itself and put a short jumper from the big positive post to the small one. That enables me to push the button to activate the relay without having to turn on the ignition.
Starting routine on a "cold" day in Arizona at 3,800 feet elevation is to push the button for ten seconds. Turn on ignition and wait until I hear the air bubbles burp through the fuel pressure regulator and turn the key.

 

After a few days of checking the truck's ability to start with the GP disconnected I'm satisfied that my problem is most likely poor cable contacts at the batteries. With the GP disconnected the cranking rpms and voltage are substantially higher resulting in very quick starts. I've replaced and cleaned some of the cable ends with cheap clamps while I wait on the correct parts to permanently fix them.
I also ordered a switch from the folks Sous recommended and plan on installing it to operate the GP circuit when needed. Hopefully when my wife drives the truck she'll be reminded to glow the plugs while the wait to start light is on when she starts the truck on cold mornings. If there's no light she'll forget. I have to turn off lights, close doors, etc. because of her absent mindedness, she's an artist and is often in her own world (drives me crazy sometimes).
Once again thanks for walking me through this problem. I quit twisting wrenches a while back and it takes an act of will for me to perform basic maintenance let alone do modifications to my various vehicles and farm equipment, however there's always something needing fixing.

 

I live this. My wife is of the artsy mind. My daughter is an artist (school for art teacher as we speak). Son is a musician. I’m the only
mechanical brain type in the house.

Looking forward to hearing all about your resolution to the issue.

 

How old is that starter?