New m1028, crank no start

[erasedhammer]

New to the cucv crowd, previous humvee owner.
Just picked up this new m1028, and the guy put in a new 24v starter, and I just threw in two brand new batteries.
Unfortunately the original starter relay was replaced and relocated to the engine bay firewall.
I saw the doghead relay mod and that had 4 connections on its relay, current one I have has 3.
Also not sure what voltage the relay is supposed to be handling, but the sticker on it says 12v.

I know that my crank no start could be no fuel/glow plugs issue, but for now I'm focusing on the starter circuit since it looks like it was hacked up and replaced by someone not familiar with these trucks.

 

[cucvrus]

I suspect that is a relay for the glow plugs. The starter relay is up under the dash where the stock radio would be. I could be wrong. But pictures are hard to tell. The battery hold down and batteries are in need of some attention. Do both batteries have good CCA and have they been load tested? Report Back please.

 

[erasedhammer]

I suspect that is a relay for the glow plugs. The starter relay is up under the dash where the stock radio would be. I could be wrong. But pictures are hard to tell. The battery hold down and batteries are in need of some attention. Do both batteries have good CCA and have they been load tested? Report Back please.

There is no relay under dash. The one in the picture is the starter relay, cause if I disconnect it, engine doesn't crank.
Both batteries have been tested good.

The truck in it's entirety needs attention. I just want to get it running then I'll be deep cleaning it.

 

[royalflush55]

Be careful not to let battery hold downs come in contact with battery terminals or you will be chasing more problems!

 

[erasedhammer]

Well I just checked fuel, it's getting it to the injectors
Although the flywheel is chewed up. Missing a large portion of the teeth. So I guess I'll be replacing it before I can get it running

 

[Terracoma]

I saw the doghead relay mod and that had 4 connections on its relay, current one I have has 3.

The stock/Doghead relay has 4 wired connections because the relay does NOT ground through its own mounting bracket.

Your current relay is most likely self-grounding.





The yellow wire seen above on your current relay is the trigger wire, and is most likely tied into either circuit #5 or circuit #930E (as found on Diagram F-1 in the -20 manual) to close the relay. Best bet is to check the cabin side of that grommet and locate the origin of that yellow wire. Photos can help us confirm.

The pink wire attached to the driver's-side of your current relay (closest to the windshield wiper motor, as viewed in your photo) is circuit #6 (from the same Diagram F-1) and goes down to the starter solenoid... You can see the remnants of the circuit sticking out of the bulkhead connector where it was cut. On the cabin side of the bulkhead connector, circuit #6 would have gone to the stock/Doghead relay under the dash.

Your photo does not show the origin of the red wire attached to the passenger's-side of your current relay (closest to the brake booster, as viewed in your photo), but it should go to a 24v power source for the 24v starter to function properly... It doesn't look like circuit #2Y has been cut, based on your photo, so your current relay is sourcing it's 24v power from somewhere in the engine compartment. Follow that red wire and let us know where it originates.



EDIT: I've attached Diagram F-1 below, but getting cozy with the CUCV TM's is always recommended.

View attachment Diagram F-1.pdf

 

[erasedhammer]

Here are some photos. I'm new to the cucv wiring, and so far the wiring looks pretty bad from the previous owner.

 

[Terracoma]

The large bundle of electrical tape above your fuel filter housing...are all of those wires spliced together under the tape?

Just confirming that none of that wiring is connected to the upper bus bar.







Your current starter relay appears to be pulling 12v power from the glow plug relay, as I've noted above, which I don't think is electrically correct... While the starter solenoid should actuate with only 12v, the side effects will be detrimental to the solenoid and the wiring in the long run.

The solenoid is actuated in the stock/Doghead system with 24v.






Just a best guess here, but I think the yellow wire that I've noted above is your current starter relay's trigger wire... See if you can follow this yellow wire and let us know where it originates.

Is the stock/Doghead wiring still intact where the starter relay is supposed to be? If so, it looks like you might be able to return this system to stock (so that it matches the TM wiring diagrams) without much trouble... But we need to confirm that the stock wiring is still intact, to the passenger-side of the above photo.

 

[erasedhammer]

Under the tape is spliced together. I can wire something together to at least get 24v to the relay, but where do I grab the 24v?

 

[Terracoma]

...I'm only recommending this under the assumption that you're 100% certain that the starter is a 24v model...

The quick and dirty method will be to connect the passenger-side of the current starter relay directly to the upper (+) 24v bus bar... However, you will want to protect this circuit with a fusible link, as was done on the stock 24v system. The stock system used a 16-gauge fusible link to protect the 12-gauge power wire between the bus bar and the relay.

EDIT to add: the above recommendation will duplicate a wiring circuit that appears to still exist on your truck... I only recommend it as a temporary solution, until you can verify the condition of, and replace the stock starter relay and wiring with the Doghead version.









SECOND EDIT for clarity: the above recommendation involves completely REMOVING the below shown wire...

 

[erasedhammer]

Went ahead and removed that short piece from the glow plug relay to the starter relay and ran some 10 gauge wire from the 24v shunt to the starter relay. Starer now runs at correct speed, but my flywheel is missing almost 80% of its teeth, so I'll have to get the truck towed to a place where I can swap the flywheel.

 

[Terracoma]

Bummer about the flywheel...



All in all, the wiring actually doesn't look too bad...just needs a few things rerouted, reconnected, or performed a little differently.

The wiring that feeds the glow plug relay is not ideal, as the full current load of the glow plugs is being supplied without any overload protection... Good practice would be to route the large red cable feeding the glow plug relay directly to the front battery positive (+) terminal or to the rear battery negative (-) terminal, and protect it with a suitable link, fuse, or circuit breaker. That splice above the fuel filter housing should be undone, and the red 8-gauge wire should be reconnected back to itself.

Additionally, since you have fuel to the injectors, that leaves a non-functional glow plug system as a possible culprit for a no-start condition... You'll need to verify that the glow plug relay is closing when the key is turned to the "on/run" position, and that each plug is actually glowing when the relay closes. If the relay does not close, then you'll need to troubleshoot why.

Given some of the the modifications by the previous owner, I'm guessing that your truck has a non-functional glow plug card, or is missing the card entirely. When faced with glow plug card problems, most users substitute a push button switch to fire the glow plugs. While not ideal, it is usually adequate enough to get the truck the start. The glow plug card should be housed inside a black plastic box, usually hanging near the steering column inside the cabin.



Let us know what you find, and we can direct you further.

 

[cucvrus]

Went ahead and removed that short piece from the glow plug relay to the starter relay and ran some 10 gauge wire from the 24v shunt to the starter relay. Starer now runs at correct speed, but my flywheel is missing almost 80% of its teeth, so I'll have to get the truck towed to a place where I can swap the flywheel.

FYI. You can change the flexplate without dropping the transmission out of the truck. I just wanted to put that out there for you. You will need 4 3/8" x 4" grade 8 bolts.

 

[erasedhammer]

FYI. You can change the flexplate without dropping the transmission out of the truck. I just wanted to put that out there for you. You will need 4 3/8" x 4" grade 8 bolts.

Yeah I found someone's write up on the job. I'll be doing it tomorrow. Gonna stop by Fastenal and pick up the bolts.