Humvee intermittently won’t start

[Rob5]

Having a problem. Most of the time the vehicle fires right up. Other times I make sure I’m in neutral, turn the start switch to the run position, wait for the glow plug indicator light to go out, turn the switch to the start position, and either nothing happens, or I here a ticking sound coming from somewhere under the dashboard or under the hood above my feet. It seems to be happening more frequently. The other night after several tries I gave up, then came out the next morning and on the first try it ticked a few times, then on the second, it started.

The climate is warm where I am, so I don’t think changing the glow plugs will help, and my batteries are new. I suspect it is either the starter solenoid or the glow plug control box. Has anyone had this problem? Both of the aforementioned parts are fairly pricey, so I’d like to avoid replacing both.

 

[Dock Rocker]

Have you confirmed all of the battery leads are on tight with zero corrosion?


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[Rob5]

Leads we’re a bit loose the first time it happened, but they are very snug now, and it’s still happening. Not much corrosion, but I could try disconnecting, cleaning, and reconnecting.

 

[Bulldogger]

Leads we’re a bit loose the first time it happened, but they are very snug now, and it’s still happening. Not much corrosion, but I could try disconnecting, cleaning, and reconnecting.

Tight on the outboard side of the connections too? Under the truck, looking at the outside of the battery compartment near the starter? That's a two headed lug, for lack of a better term, and needs to be tight on both sides. Common issue. BE CAREFUL checking that one, as you're moving a wrench around in tight quarters on 24V hot side on one of those fittings.

It's also worth taking those apart and cleaning them, if you can make the time, as they are almost surely corroded, even if some soldier coated them in RTV (like mine!).

Started connections should be checked next, as clicking can be the solenoid as already stated, but I strongly encourage disconnecting, cleaning and reassembling all connections.

I'll throw in a recommendation for installing a grounding harness, if you haven't. There are some good threads on that, so I won't go into detail here. Small cost if you make it yourself and it improves reliability in the opinion of many of us.

Bulldogger

 

[Action]

Why not disconnect the batteries before putting wrenches around the starter.

 

[papakb]

This is characteristic of the early Prestolite protective control boxes beginning to fail. Also characterized by a loud "clunk" when the start switch goes into the run position. The USMC "fix" for this was a swift kick straight up into the PCB with your left foot! LOL

 

[Rob5]

Thanks. Advice much appreciated.

 

[papakb]

The Prestolite control boxes are the oldest and are probably the simplest and easiest to repair. Open it up and all you'll find are some 24v starter solenoids which are pretty easy to change out. One of the solenoids is a reverse power relay in case you hook up the batteries backwards and that's the one that "clunks" when you first switch to "RUN". It's also the one that usually fails first because it cycles every time the truck is turned on. So after 30 years it's getting tired. I put a little switch inline with the coil and when switched open it won't allow any power to the truck. A simple, unobvious disable feature.