Did I toast my 6.2 engine somehow, and how do you jump a 24v HMMWV?

I'll try to make a long story short.

I had a Freon leak so I needed to replace the condenser and recharge. I got the new condenser plumbed in but I still have to fab up some new brackets as the replacement was just a bit wider than the original for some reason. I wanted to charge the system and make sure it had no leaks. To I pull a vacuum, and satisfied, I just let a can of Freon push itself into the system so I can double check it with my electronic leak detector before fully charging it. Looked good.

So I go to start the engine, and it wants to piss me off and the starter grinds, and won't spin the engine. I was really bummed out so let it sit for a couple days. I thought I might be looking at a flex place replacement and I really, really did not want to have to drop the tranny.

So today I pull edthe starter and it looks ok, but there is a bit of ware on the front of the teeth. Thankfully, I caught a break and looking at the teeth on the flexplate, they seemed to look good. No abnormalities seen in the flex plate.

So I have a spare starter that was rebuilt by a local shop, and I slap it in, using the same two shims and bolts from the previous one.

Go to crank it and it grinds again.

I take a breaker bar and throw it on the bolt on the crank and I spin it by hand for a few revolutions. In one spot it gets harder to turn but not really locked up or anything like that, and I hear a whoosh which I assume is compression, and after getting past that it seems easier until I hit that hard spot again on the next revolution. So I leave the crank in an easy to turn spot.

I try cranking again and I see it rotate for a little bit and then it grinds again.

So I thought I better cool off and not throw anymore parts at it, although they were spares. And seek the wisdom of the collective on what to do next. I am next thinking could it be the batteries? They are on a NOCO dual bank trickle charger all the time, but I guess Odyssey 6TL that is two years old can go bad.

But I am stumped how to jump a HMMWV with only 12V cars around to jump with? I have one 12V jump pack. I googled a bit and HF has a 24V jump pack, but I really don't want to spend $340 for it.

So what would you guy recommend I try next?

Thanks in advance!

You can jump a 24v vehicle from two 12v vehicles.

Connect each 12v vehicle to the positive and negative of one of the HMMWV batteries using heavy duty jumper cables. Ensure that the 12v vehicles are not electrically connected to each other in any way.

I would be shocked if a 2 year old Odyssey was bad unless it sat dead for a long time.
Did you inspect the teeth all the way around the flex plate?
There should be 4 "tight" spots per crank revolution, if you have a tight spot in only one place EVERY revolution something seems wrong.

Here is how it looks jumping from 2 12V jump packs.
Replace one of them with the jumper cables from the 12V vehicle.
2 12V batteries, each one gets a 12V source.



That being said, you need to put a multimeter on the batteries and see what they are actually doing while you are cranking. If they stay above 22V or so while trying to crank, then it likely isn't a battery issue, but could be a bad connection somewhere in the system. You can also check each individual battery while trying to crank, and they should be about the same. If one drops lower, then it may have a bad cell.
If all else fails, take the batteries out and to your local auto parts store. Most stores have battery testers, either the old carbon pile type or newer capacitive. Or buy a capacitive tester of your own, they start around $40 on amazon.

The pass through bolt on the DC Shunt in the battery bay has been found to be a little loose on multiple trucks, leading to starting issues, so that would be one place to check.

When my batteries were low, I never heard any grinding. The starter engaged, but just didn't have enough force to rotate the engine properly, until voltage dropped too low and starter disengaged and attempted to reengage.

Coug said:

When my batteries were low, I never heard any grinding. The starter engaged, but just didn't have enough force to rotate the engine properly, until voltage dropped too low and starter disengaged and attempted to reengage.

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Same here. That is why at first I thought I was going to be dropping the tranny (again) to replace the flexplate. When I converted from a TH400 to a 4L80 I replaced the flexplate (and new starter and old one rebuilt) as I saw it was missing teeth.

Mogman said:

There should be 4 "tight" spots per crank revolution, if you have a tight spot in only one place EVERY revolution something seems wrong.

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Exactly! It seems that on every revolution of me cranking it with a breaker bar, I get to one hard spot, and the rest of the revolution it goes easy.

Yeah - that's my fear - something smoked in one or two cylinders and new engine time Since it gets hard in some spot on every revolution, I am guessing it's two cylinders.

I'll take a break from it till I get an idea. I don't want to grind down a fresh starter nor the flexplate. I would have it towed to a professional mechanic, but there are not any that work on these rigs around here - at least on the tough problems.

FlameRed said:

Same here. That is why at first I thought I was going to be dropping the tranny (again) to replace the flexplate. When I converted from a TH400 to a 4L80 I replaced the flexplate (and new starter and old one rebuilt) as I saw it was missing teeth.



Exactly! It seems that on every revolution of me cranking it with a breaker bar, I get to one hard spot, and the rest of the revolution it goes easy.

Yeah - that's my fear - something smoked in one or two cylinders and new engine time Since it gets hard in some spot on every revolution, I am guessing it's two cylinders.

I'll take a break from it till I get an idea. I don't want to grind down a fresh starter nor the flexplate. I would have it towed to a professional mechanic, but there are not any that work on these rigs around here - at least on the tough problems.

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Pull the glow plugs and see if you have a hydro-locked cylinder, also only turn an engine in the normal direction, that would be trying to tighten the harmonic balancer.

Mogman said:

Pull the glow plugs and see if you have a hydro-locked cylinder, also only turn an engine in the normal direction, that would be trying to tighten the harmonic balancer.

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Except that I have two glow plugs broken off, one in each bank. I guess I could try to remove the others or how hard is it to pull the injectors? I guess I could try first pulling the three glow plugs on the driver's side that are not broken off and see if I get lucky. Probably will break off more seeing my luck these days.

But yeah, it is acting like it is hydrolocked, or got a bent pushrod, or some piece of garbage got into the engine.

Start by checking the individual voltage of each battery, than load test each battery…
engines don’t just hydrolock themselves unless they ingest water

Retiredwarhorses said:

Start by checking the individual voltage of each battery, than load test each battery…
engines don’t just hydrolock themselves unless they ingest water

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I admit that I had the air intake tube off for a few days while I was (attempting) to service the AC and replace the condenser. I tried to be careful and put a plastic bag, rag and then a weight to hold them down on the manifold air opening, but obviously that was stupid on my part and maybe something crawled into the engine

FlameRed said:

I admit that I had the air intake tube off for a few days while I was (attempting) to service the AC and replace the condenser. I tried to be careful and put a plastic bag, rag and then a weight to hold them down on the manifold air opening, but obviously that was stupid on my part and maybe something crawled into the engine

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Was the hood closed?
Did it rain?

Retiredwarhorses said:

Was the hood closed?
Did it rain?

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The hood was closed. It did rain once.

FlameRed said:

The hood was closed. It did rain once.

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That intake is directly under the seam between the hood and the cowling.
Pull the glow plugs that you can and see if the "tight spot" goes away.

GM engines are known for breaking flex plates.

I honestly don’t understand where this is going. I don’t see a diagnosis yet. I don’t understand what everyone’s talking about battery chargers.

If this gentleman is able to turn the engine by hand for several revolutions, in my mind that goes against Hydro lock because Hydro lock would not easily release unless the glow plugs or fuel injectors were removed.

The flex plate is not properly described to me because, as someone asked above, I am not clear that every tooth was examined and every tooth is intact. I also don’t know that the flex plate is not warped.

This gentleman replaced his starter, but did he use shims? That has not been described.

Batteries could be suspect and should be removed and taken to a local auto shop that can charge them and then load test them to see if they are putting out enough amperage.

The first things I would check however, are that I would clean and replace the battery connections to see if there is poor connection causing problem. The next thing I would do is make sure that the engine side and dashboard side of the plugs that enter the glow plug module/protective control box/smart box are properly secured

Good luck OP.