From: chance wolf (chance_wolf@shaw.ca)
Date: Sat Jan 10 2004 - 17:09:34 PST
----- Original Message -----
From: "Scuba Steve" <me_scubasteve@yahoo.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Saturday, January 10, 2004 3:56 PM
Subject: [MV] Looking for a humvee control box?
> Hi List
> Me again, I have an M998 and I am not getting power
> to the glow plugs. Any ideas? Are there any ground
> wires I could check? Or does anyone know where I can
> find a new control box. I was thinking of pulling the
> box out of my other humvee and trying in there but I
> would rather not mess with that truck. Thanks for the
> help.
> Scuba
They come out very, very easily, and you'll be doing yourself a favour by
"troubleshooting by subsitution of a known working unit" through exchanging
the suspect one with the one you know works. Saves buying stuff on spec.
If the replacement box gives you power to the glow plugs, then swap the
defective one back in just to make sure it's still defective, and that
you're not dealing with some sort of harness intermittent instead.
Also, make sure you're checking the voltage to the plugs with the engine
cold, and the test light hooked up BEFORE turning the ignition switch to
'ON', and that you can see the test light from wherever you're turning the
switch on. You should be hearing the glow plug relay in the PCB go 'clunk'
as you turn the IGN switch to ON, and the test light should light up for the
duration of the glow period. If you hear the 'clunk' but don't see the test
light turn on - it's more than likely going to be the PCB or the harness
itself as if the sensor in the water crossover was defective, the PCB would
get no turn-on signal and you'd hear no 'clunk'.
If you're hearing nothing from the PCB when you turn the ignition switch on
(and the engine is cold), it could still be the PCB itself, or it could be
the sensor screwed into the water crossover. There are two problems with
that thing: 1) The early versions of the harness plug allowed water and dirt
to contaminate the connections beneath the plug, and; 2) The early version
of the temp sensor was a mechanical/bi-metal strip affair and a guaranteed
fail after X-miles, and the first version of the electronic type wasn't
supposed to be much better. You can tell by the colour of the metal part
where it screws into the water crossover if memory serves. I think the
early black (silver?) ones suck, where the later ones with the O.D. coloured
metal at the bottom are the good type. Hopefully someone on the list can
either corroborate or debunk that one, as I'm just going by memory.
If you have occasion to open up one of the defective early PCB's just for
education's sake, you'll see a printed circuit board and several relays
quite like the 'silver can' glow plug relay fitted as a replacement to the
CUCVs. Depending on the manufacturer, some are repairable, and some are
covered in either epoxy or this sort of black silicone goop to the point you
can only recognize the wires and relays in silhouette. About a pint of
nice, filthy water came out of the one I removed from a Humvee which was
having some truly flakey electrical system problems, and I have another I
strongly suspect of the same thing. Either way, those relays are only good
for just so many make/break cycles before they break themselves, so you
could well hear the armature 'clunk' of the one tasked with running the glow
plugs and still not have any connection made between the B+ input/output
terminals themselves. Especially if it dates from 1985.
Anyway, with your Ignition switch ON, engine cold, test light hooked up -
wiggle the wiring harness where it screws into the top of the PCB under the
hood above the driver's feet. If you hear clunking, either the physical
metal-to-metal connections are dodgy, or you have an intermittent solder
connection in the harness itself. If wiggling does nothing, then move on to
your PCB swap. Fun fun fun.
(but before any of it, check to see you have engine ground with a meter as
described in the other post or this will all be pointless)
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