No-start issue : Where to begin

[87M998X62]

So I have an 87 M998 6.2 that has been sitting for a few years. It ran well back then, but slowly developed a starting issue back in early 2021.

In trying to get it road-worthy now, I just need some direction of where to begin. Here is how the trouble began:

It would crank intermittently, on and off. As in, switch on "start" and the starter would kick in and out like morse code...as if there was a bad and arcing connection somewhere. The last time it ran it at least did it enough to turn over, but it was a task. Then, it would crank a bit and the bendix would retract while the starter was still spinning. As more time passed, it just degraded to leaving it on the "start" position, and the starter would kick here and there, but for a split second...not long enough to crank at all. It still remains that way...but mostly now, there's no sign of life beyond the glow plug circuit seeming ok.

I did start cleaning up connections wherever possible, starting with the starter itself and the wiring near the battery. I haven't checked other things like the neutral safety. What concerns me is that this just slowly degraded to not starting at all. I am assuming I just need to keep going through wiring and grounds to see where a bad connection exists, but any other input would be greatly appreciated!

 

[NDT]

Check the cannon connectors on the protective control box, there can be corrosion on the wires entering the connector pins which can lead to intermittent continuity you describe. Starter could be shot too.

 

[Mogman]

There are positive and negative connections on both the inside and outside "tunnel" of the battery box that should also be checked.

 

[87M998X62]

Check the cannon connectors on the protective control box, there can be corrosion on the wires entering the connector pins which can lead to intermittent continuity you describe. Starter could be shot too.

Ok I will look at this when I get out there next. Thanks for the pointer! I know it just has to be a bad connection somewhere I haven't found yet...it ran like a top prior to 2021.

 

[87M998X62]

There are positive and negative connections on both the inside and outside "tunnel" of the battery box that should also be checked.

Yeah I cleaned these up already... everything in that area. They were in need of some sandpaper for sure....

 

[MarkM]

Use crocus cloth as it's far better than sandpaper on electrical connections and leaves less debris. Just my .02 cents.

Mark

 

[tomelroy]

i would start by load testing each battery...proceed from there

 

[87M998X62]

i would start by load testing each battery...proceed from there

I'll look into that too.. The batteries are over 5 years old at this point but I store them in my garage and top them off periodically.

 

[87M998X62]

Ok, so I checked both connectors on the protective control box and everything looked clean as can be. I cleaned the ground on the back of the motor on the drivers side... charged up both batteries.. aaaand nothing. Now the glow plug light was flickering and dim, and still no cranking at all. I really dislike electrical issues... I'm not the best at diagnosing them, as I know the next step is the multimeter with a needle on the probe to start poking through wires.

There is power at least when I turn the ignition on...

 

[Hummer Guy]

Ok, so I checked both connectors on the protective control box and everything looked clean as can be. I cleaned the ground on the back of the motor on the drivers side... charged up both batteries.. aaaand nothing. Now the glow plug light was flickering and dim, and still no cranking at all. I really dislike electrical issues... I'm not the best at diagnosing them, as I know the next step is the multimeter with a needle on the probe to start poking through wires.

There is power at least when I turn the ignition on...

How does your battery terminals look? And did you check the voltage on the batteries? Those batteries could be toasted.

 

[87M998X62]

How does your battery terminals look? And did you check the voltage on the batteries? Those batteries could be toasted.

The terminals and cables look good, and both batteries just came off of the charger before I tried it again. I will say I haven't had it running in a couple of years and prior to that I only ran it around the block once in a while.. so the batteries didn't get used much.. but I have stored them in my garage. I would be somewhat surprised if they were bad....but I guess I could easily get them load tested at a local parts store...

 

[Hummer Guy]

The terminals and cables look good, and both batteries just came off of the charger before I tried it again. I will say I haven't had it running in a couple of years and prior to that I only ran it around the block once in a while.. so the batteries didn't get used much.. but I have stored them in my garage. I would be somewhat surprised if they were bad....but I guess I could easily get them load tested at a local parts store...

Yea, get them load tested before you move on, a dead battery would drop dead soon when that charger is unhooked.

 

[Konu123]

Hope this helps. The bottom white board pic is a class I taught on no crank/no start. Check cca’s on battery, then give starter wiring a visual check and make sure it’s right, then try bypassing the smart start box(pcb box) by taking a paper clip with electrical tape in the middle and connect (with the truck off) T then S on the diagnostic port next to the shifter and try to start (if starts it’s the pcb), then bypass the neutral safety(make sure it’s in park) by jumping the two wires. Then check switch wiring(I’m assuming that’s not it since it was cranking but might). If all are done and still doesn’t start, it’s the starter.

 

[87M998X62]

Hope this helps. The bottom white board pic is a class I taught on no crank/no start. Check cca’s on battery, then give starter wiring a visual check and make sure it’s right, then try bypassing the smart start box(pcb box) by taking a paper clip with electrical tape in the middle and connect (with the truck off) T then S on the diagnostic port next to the shifter and try to start (if starts it’s the pcb), then bypass the neutral safety(make sure it’s in park) by jumping the two wires. Then check switch wiring(I’m assuming that’s not it since it was cranking but might). If all are done and still doesn’t start, it’s the starter.

Ok thank you! I will do this sequence next. Just out of curiosity, and please forgive me if the Googles had this answer already, but is there a more "inexpensive" starter that still fits and works? I see different places charging $500-$600 for a starter, but I don't know if there's an "over the counter" option..?

Also, in doing some research, I came across this article:

Know the Difference Between the HMMWV 6.2L and 6.5L Detuned Engines

There’s confusion when it comes to identifying the 6.2L and 6.5L detuned engines used in basic and A1 HMMWV models. How do we know? TACOM LCMC says the HMMWV engine repair program is receiving uns…

halfmastpsmag.wordpress.com

Now the interesting thing is I know that other older M998s would be fitted with "overhaul" plates (or writing) indicating when they had the motor swapped from a 6.2 to a 6.5... mine is a 1987 and has no such writing, yet based on this article and the location of the mounting bolt, I apparently DO have the "de-tuned" 6.5 liter engine... and also, it looks to have the tachometer drive attached, but I have no tachometer....

 

[CapePrep]

This is on my engine, just an FYI

 

[Konu123]

Ok thank you! I will do this sequence next. Just out of curiosity, and please forgive me if the Googles had this answer already, but is there a more "inexpensive" starter that still fits and works? I see different places charging $500-$600 for a starter, but I don't know if there's an "over the counter" option..?

Also, in doing some research, I came across this article:

Know the Difference Between the HMMWV 6.2L and 6.5L Detuned Engines

There’s confusion when it comes to identifying the 6.2L and 6.5L detuned engines used in basic and A1 HMMWV models. How do we know? TACOM LCMC says the HMMWV engine repair program is receiving uns…

halfmastpsmag.wordpress.com

Now the interesting thing is I know that other older M998s would be fitted with "overhaul" plates (or writing) indicating when they had the motor swapped from a 6.2 to a 6.5... mine is a 1987 and has no such writing, yet based on this article and the location of the mounting bolt, I apparently DO have the "de-tuned" 6.5 liter engine... and also, it looks to have the tachometer drive attached, but I have no tachometer....

Not sure I’m a mechanic in the military I don’t even know where we get our parts from tbh they probably cost $1000 where we get them haha. But I’d try these steps and get someone to crank while you wack the starter solenoid with a hammer first. If it doesn’t start take it out and bench test it before buying.
Found a website with a starter for $395 starter with a $225 core charge though, pretty sure the starters the same for all 6.2’s and 6.5’s could be wrong though.

24 Volt Electric Starter 6.2L & 6.5L GM Style Diesel Engine HMMWV

24 Volt Electric Starter 6.2L & 6.5L GM Style Diesel Engine HMMWV

www.easternsurplus.net

 

[Mogman]

Ok thank you! I will do this sequence next. Just out of curiosity, and please forgive me if the Googles had this answer already, but is there a more "inexpensive" starter that still fits and works? I see different places charging $500-$600 for a starter, but I don't know if there's an "over the counter" option..?

Also, in doing some research, I came across this article:

Know the Difference Between the HMMWV 6.2L and 6.5L Detuned Engines

There’s confusion when it comes to identifying the 6.2L and 6.5L detuned engines used in basic and A1 HMMWV models. How do we know? TACOM LCMC says the HMMWV engine repair program is receiving uns…

halfmastpsmag.wordpress.com

Now the interesting thing is I know that other older M998s would be fitted with "overhaul" plates (or writing) indicating when they had the motor swapped from a 6.2 to a 6.5... mine is a 1987 and has no such writing, yet based on this article and the location of the mounting bolt, I apparently DO have the "de-tuned" 6.5 liter engine... and also, it looks to have the tachometer drive attached, but I have no tachometer....

If anytime in the recent past it needed an engine it would have received a 6.5L the 6.2L has been out of circulation for a long time and that does not mean your machine went through a "rebuild", also that is not a tach drive that is only used by the diag. port to test the RPMs, the tachs drive off of the alternators

 

[87M998X62]

If anytime in the recent past it needed an engine it would have received a 6.5L the 6.2L has been out of circulation for a long time and that does not mean your machine went through a "rebuild", also that is not a tach drive that is only used by the diag. port to test the RPMs, the tachs drive off of the alternators

Well you learn new things every day! Thanks. I don't always do the best homework before asking things, so I greatly appreciate the input from those who know better. I just saw the "overhauled on (date)" on others that had motors swapped and assumed it was standard practice.

At least I have a list of things to look at this weekend...

 

[87M998X62]

Well.. batteries checked out fine. On to the rest of the tests!