Hard Start Only On Cold Start

[K9TRACKER]

I have a M998 with the 6.5 non-turbo. On the first crank after its been sitting for at least a few minutes it struggles to start almost like the starter is having a hard time turning the engine over. The starter is new, the batteries are new, the brainbox is new, the glowplugs are new. The wait light works and the glow plugs preheat. Here's a link to the video of it hard starting https://streamable.com/lsnwr9

I'm beginning to think an injector is stuck open and leaking down into a cylinder when its not running causing the hard start because if you turn if off and immediately restart it it starts fine with no hesitation, its only after it been sitting a few minutes that it hard starts.

 

[Mogman]

WELCOME TO THE FORUM!!
If the engine is warm than it is not glow plugs, that sounds horrible when starting I wish you had included a few more seconds when running, sounds like the engine may be timed incorrectly.
The two things I would do is run a cylinder balance test, cracking open each injector and noting the RPM drop for each cylinder, this should indicate if you have a leaking injector.
The second would be to disable the IP (injection pump) by pulling the run wire off of the IP and see if it still sounds so bad when just spinning the engine over without actually trying to start.

 

[K9TRACKER]

The engine runs fine once its started - no running issues at all, drives down the road fine. It also starts every time. It only sounds bad on the first crank when its been sitting for at least a few minutes.

 

[K9TRACKER]

Here is a longer video, https://streamable.com/pnqp63
Started better this time but its only been sitting for about 30 minutes - the longer it sits the worse it sounds on initial start-up.

 

[Milcommoguy]

Well... here a free guess after seeing the switch. Might be flaky voltage to the solenoid not pulling in hard. I here a chatter sound like it is banging on the ring gear struggling to spin up.

This is my over the internet free guess and we all know how that works.

Pat, I like to buy a vowel, CAMO

 

[Mogman]

Oh yes new information, get rid of that key switch, well known faux pas in the HMMWV world

 

[Mogman]

That big honkin starter solenoid pulls too many initial amps for a key switch and the reverse EMF arcs the crud out of those switches

 

[Mullaney]

Here is a longer video, https://streamable.com/pnqp63
Started better this time but its only been sitting for about 30 minutes - the longer it sits the worse it sounds on initial start-up.

.
Go buy yourself a FACTORY start switch.
Your problems will disappear.

.

 

[jake20]

This right here is the real deal: https://www.hummerpartsguy.com/SWITCH-IGNITION-WITHOUT-LEVER-24-VOLT_p_24452.html

AM General discontinued a previous version of the switch, don't remember the NSN off the top of my head. That one with the black metal casing and brass colored band is the correct REAL and active production revision of it. HPG is the only vendor I was able to get a real switch from, rest were either reproductions that leaked voltage or just flat-out broke internally (I tested from 3 other vendors or so, the switches were all brass colored as well).

The start switch on these trucks seems like such an innocent piece, but it is in fact critical to have the right one. Don't risk burning up starters and chewing flexplate teeth due to iffy engagement.

 

[jake20]

Actually - HPG being as detailed as they are, here is the description for one of the incorrect revisions:

"11614131 IS AFTERMARKET (SILVER BODY WITH LEVER INSTALLED) IT IS ACTUALLY A 5 TON SWITCH (AND CANCELLED NSN IN 2018 ) THAT DOESN'T FIT A HUMVEE AND BURNS OUT STARTERS"

And a snippet from an email thread I had with them:

"There is only 1 switch with the correct nsn...12506826 / 01-593-1045 (since 2011)..if somebody is sourcing the old switch PN# 11614131 / 01-614-3597 you should tell them it was cancelled in 2018"

Once again - stupidly innocent seeming piece but absolutely critical.

 

[K9TRACKER]

Unfortunately this problem occurs with the factory switch and the aftermarket key switch. Key switch has only been in it for a couple of days.

 

[jake20]

I'd still yank that key switch to prevent any fires down the line, Kascar sells a fuel cutoff keyed switch that ties in-line to the injection pump fuel cutoff wire. This would still let someone crank the truck, but they'd never get it started if there's no power going to the injection pump fuel solenoid.


Also, avoid the push-button style light switches, they start fires too.


In terms of the issue at hand, I don't have much more to offer at the moment aside from what the others have said. Only other thing I can think of without more information is just making sure all the starter terminals are clean and tightened down properly. I've encountered 2 trucks already that have had loose starter cabling from auction. Don't think this is quite going to solve your issue but it's a good thing to check anyway.

 

[K9TRACKER]

We've triple checked all the connections - I have a grounding harness for it that just came in and we're going to do the cylinder balance test later and try cranking with the injection pump unhooked to see if that changes anything with the cranking. I'll update you all after we do it. Thanks for the info guys.

 

[jake20]

Happy to help, let us know how it goes. The more we know the merrier

 

[Milcommoguy]

Unfortunately this problem occurs with the factory switch and the aftermarket key switch. Key switch has only been in it for a couple of days.

Well... it was a free guess. Time to dig a little deeper. Check voltages thru out the starting circuit under loading conditions. Electrical connection nice and tight? Mechanically, starter parts not playing nice, busted, rusted ?

Time to get the creeper and volt meter out, CAMO

 

[jake20]

For what it's worth, here are the videos I took of my troubleshooting of the start solenoid power:

 

[Gcelevator]

Did you hook up your starter as a 12V by chance? Possible and makes a weird noise. Not enough juice to start properly unless the engine is hot. Worth to check.

 

[K9TRACKER]

We finally figured this thing out about a month ago. Just letting you all know what we found. It ended up being the Protective Control Box, we had replaced it because the old one wasn't letting the alternator charge. We had originally replaced the factory box that was bad with a new aftermarket one from Seco
(see attached picture for the junk one ). We finally figured out these boxes were the problem because we had two of them for two different trucks and when we put the other one in another truck it started the same as the one we have been trying to fix. We ended up ordering two OEM control boxes and boom problem solved. So I'd advise anyone who needs a protective control box to avoid these cheaper aftermarkets because you'll just end up spending more money in the long run. I think we've spent about $2500 on control boxes because we couldn't return the junk ones because we had had them for about a year, but they did give us a discount on the OEM ones.

 

[jake20]

I’ll chime in here, only ever get the KDS S3 box nowadays, all the other ones have been obsoleted. The KDS S3 paired with the correct TSU is the most recent revision and simply works, no questions asked. You can buy a full set from HPG. I can’t attest to trucks but the KDS S3 will work on any A2 or above. You know it’s the right box if you see an additional diagnostic cannon plug near the center of the box, same side as the interior cannon connector.

if it says PCB anywhere I’d avoid it at the risk of burning plugs more often or other weird issues. Definitely avoid all SSI brand boxes, certain serials were known to burn trucks down after spontaneously starting up.

A lot of vendors sell NOS old revision start boxes for more attractive prices, not worth the hassle, replace the box and TSU and the problem will likely solve itself

 

[Milcommoguy]

We finally figured this thing out about a month ago. Just letting you all know what we found. It ended up being the Protective Control Box, we had replaced it because the old one wasn't letting the alternator charge. We had originally replaced the factory box that was bad with a new aftermarket one from Seco
(see attached picture for the junk one ). View attachment 902212 We finally figured out these boxes were the problem because we had two of them for two different trucks and when we put the other one in another truck it started the same as the one we have been trying to fix. We ended up ordering two OEM control boxes and boom problem solved. So I'd advise anyone who needs a protective control box to avoid these cheaper aftermarkets because you'll just end up spending more money in the long run. I think we've spent about $2500 on control boxes because we couldn't return the junk ones because we had had them for about a year, but they did give us a discount on the OEM ones.

Another fortune cookie controller bites the dust. I have a few in the junk box too, But it doesn't stop there....

Buy American for your US GI Truck, CAMO