M998 Control box click

[Helio]

Hey guys, I need some trouble shooting help. I recently bought my first M998 and it would not start without starter fluid so I new right away the glow plugs were bad and maybe the glow plug controller as well, I replaced the glow plugs and did a test on the control box from a TC I uploaded and it tested the controller was bad. I replaced the controller and it snowballed from there and I replaced a bunch of things clear into the water pump... I got everything back together and when I went to start it I turned the key to the on position and it made a (clunk) click sound coming from the control box and the wait and brake lights went off right away, it did that every time I tried it which was only 2-3 times. I automatically thought it was a bad new controller so I swapped it out with the old one and same thing. I did not disconnect my batteries totally just took the ground off one battery as I've heard they can be very sensitive and one battery tests at 12.7 and the other 11.7 so I'm confident it would start. I was also wondering I have not put the hood back on yet so the headlight harness is not connected if it needs that to complete some circuit and may be part of the problem. So here I am and I don't know what to think of the click noise or what to try next. I would appreciate any info of direction,, thank you.

 

[NDT]

Oh boy. We need to know what type start box you have. Get rid of any key ignition, go back to OEM lever switch. If the engine won’t start without either, drive something else until you fix the glow plug system. Headlight harness unrelated to starting.

 

[Helio]

Oh boy. We need to know what type start box you have. Get rid of any key ignition, go back to OEM lever switch. If the engine won’t start without either, drive something else until you fix the glow plug system. Headlight harness unrelated to starting.

I will look that up, the old box and the new box both have no numbers of identifying labels. I considered it being the wrong box but my old one did the same thing when I swapped it and tried right away.

 

[Action]

The older style do clunk.
How do you know if you have the correct matching GPC or TSU if you don’t know which box you have? They come in matched sets to work properly.

 

[twisted60]

Make sure both batteries are fully charged, 11.7 is kinda low. I've had the same issue when batteries were low.

 

[mgFray]

As someone already mentioned, you need to make sure you have matching TSU and Control Box. Otherwise the control box may not know if the engine is hot or cold, and won't run the glow plugs.

Also be aware the control box diagnostic steps in the TM may be incorrect for the box you have! The instructions were written to diagnose the original control box, which is no longer in use.

My M998 had a KDS box, and due to glow plug failure (and box failure, presumably), I just finished replacing the glow plugs, TSU, and EESS box with a Natron unit. Not cheap, but it fixed the problem!

Also word of advice, be sure you have "real" glow plugs, not counterfeits. One obvious sign of many of the counterfeits is a 10mm hex head on the glow plugs.

 

[Helio]

All good points, I will charge the battery now. When I order the start box the only thing I had to go by in the year and model as there was no labels … just went with the recommendation of Federal Military’s tech. I do know that it has to match with the TSU so that may be the issue, they didn’t ask and I didn’t say.

 

[mgFray]

All good points, I will charge the battery now. When I order the start box the only thing I had to go by in the year and model as there was no labels … just went with the recommendation of Federal Military’s tech. I do know that it has to match with the TSU so that may be the issue, they didn’t ask and I didn’t say.

Take a look at the box. Does it have two sockets on the front (under the dash) and one on top (in the engine compartment)? If so it's one of the newer style boxes. If you only have one socket under the dash, and one in the engine bay it's an older style box.

Below is a picture of my KDS box (sorry don't have one of the new Natron box, but it generally looks the same other then the label).



But you can see the second (not used) port on the newer boxes.

 

[Action]

Way older boxes have 2 plugs on the top in engine compartment.

 

[Helio]

Yes only one under dash and the other one is out the top next to the washer Res. I have an KDS TCU box, starto think the boxes don’t match but I’m checking all connections and charging the batteries tonight.

 

[mgFray]

I wish I could find it for you, but my search abilities have failed after a day of work... But there is a thread somewhere here with a picture of all of the various boxes and listing the corresponding TSU (or glow plug controller for the really old boxes).

 

[Helio]

I’m assuming the is an upgraded combination I can get or is that not worth it? This will probably get harder to find… Natron unit was mentioned previously.

 

[mgFray]

The Natron unit plus matching TSU are in stock at a few of the regular places. I just bought one, last week. If you want to know where from message me, don’t want to break any advertising rules.

 

[Helio]

Will do, I’ll see what happens and what I can find. Thanks everyone… I’ll let you know what I figure on this beast!

 

[86humv]

look up :
Glowplugs Never Energize and Have You Ever What the Inside of a PCB Looks Like
.
In search box