From: Julian Burke (julian@knology.net)
Date: Sat Aug 23 2003 - 12:10:33 PDT
Folks, I'm going to repost an archived article that I wrote some time ago
concerning the CUCV series which any CUCV owner will need to know about the
glowplug network. For future reference, you might want to make a hard copy
of this for your records as this information will never go out of style as
long as there are CUCV's!!.
First, I want to make every EARLIER MODEL HUMVEE OWNER aware of is a
serious recurring problem that needs to be addressed. It's the grounding
problem they all face in the wiring harness that will cause a multitude of
problems to include failure, burnout and a possible fire in the wiring!
Until you fix this problem, you need NOT try to fix other masked problems in
the electrical system until you have checked the grounding terminal. In the
earlier wiring harness, there were only about 4 or so ground wires that
GROUNDED EVERYTHING and all were terminated to one spot on the body BEHIND
THE INSTRUMENT CLUSTER. (on the right) Most of these Humvees were
exposed/forded or used around salt water OR JUST PLAIN GET DIRTY. This
terminal corrodes along with the aluminum body and causes a floating ground
which will play havoc with your electrical system. With batteries
disconnected, take this grounding point loose and clean, grind or polish
whatever it needs to make a good ground point. THIS IS VERY
IMPORTANT!!!!!!!! There is also a extra grounding harness available or you
can make or add one of your own design to supplement your existing ground
(recommended) AND IT ALSO SHOUD BE TAKEN TO THE ENGINE BLOCK AS WELL. CHECK
THIS POINT FIRST BEFORE DOING ANYTHING ELSE in the electrical system!!!!!!!
NOW FOR THE CUCV INFORMATION CONCERNING THE BYPASSING OF THE GLOWBAR
RESISTOR MOUNTED IN THE FIREWALL IN A HEATSHIELD:
POWER SOURCE FOR THE GLOW PLUG SYSTEM
Two of the most common CUCV-owner questions are, "Why did GM take the glow
plug power off the voltage dropping resistor?" and "Why not just take 12 vdc
off the normal vehicle wiring?"
GM didn't take the wire off of the resistor. What one generally encounters
is an "in house/shop" modification. This modification enhances vehicle
starting by directly routing the 12 volts to the glowplug network. The
existing resistor that has been bypassed by this method would drop the 24
volt source to 12 volts before reaching the glow plugs but this created a
problem of the the glow plugs not heating up to proper temperature all of
the time.
Here is why the resistor is used: All M-series vehicles use a NATO slave
plug to jump/slave another vehicle. If the batteries are stone-dead in a
CUCV, 24 volts will still feed the glow plug circuit and it will start when
it is slaved in its' original, unmodified condition.
It should be noted, however, that even though this modification allows the
vehicle to start easier, there is a tradeoff. If both CUCV batteries are
weak or dead and you have to slave the NATO plug with the modified setup, 12
volts will not be delivered to the glow plug circuit. This is because the
dead batteries will cause the entire 24 volts to drop to zero at the center
connection of the two batteries (where the 12 volts is sourced) until they
are charged. This is important to keep in mind when jumping off a vehicle
with this modification as it will not start through the slave recepticle
until the batteries are charged to some degree.
The modification removes the red wire from the output of the glowbar
resistor and connects it directly to the 12-volt buss (above the glowplug
relay). The terminal fits perfectly and the wire is the right length.
WHY SHOULDN'T I INSTALL A TANK HEATER?
Any CUCV that has a good operating glow plug system, will start in very cold
weather. Enough can't be said that it is also a good idea to periodically
check the glow plugs for continuity to ground and to keep a good working set
in your system! There are only two things that will hinder your diesel
engine from starting: Improper heat(ing) of the glowplugs and fuel delivery.
In warmer weather, you will not notice hard starting until at least 3 plugs
or more are bad.
Nevertheless, a tank heater wouldn't hurt. It is advisable to use one when
temperatures are below freezing for long periods of time. A tank heater will
help the engine to start faster and with much less stress due to viscid oil.
A friend mentioned that his Blazer was starting in 15 below zero Minnesota
weather without the help of a tank or block heater. I'm sure it rattled upon
starting much louder than if it had a block heater! GM has a tank heater
that fits inside of a freeze out plug that is very effective and most other
auto parts suppliers have similiary effective tank/block heaters. Even
though it might seem superfluous for the folks in the south where temps
seldom ever reach below freezing, it may be an action not worth the expense.
Nevertheless, a tank heater sure helps making the engine turn over faster on
those cold days.
The following concerns the glow plug relay in the CUCV:
GLOW PLUG RELAY
If your old Glow Plug Relay (GPR) looks like a "dimmer switch" (that is, it
appears to be made of bakelite and has a long snout), replace it now! Even
if it isn't bad, it soon will be as they rarely made it out of warranty
being a poorly manufactured part. The military upgraded this relay and the
newer one looks like a little silver can (like an older, Ford-type starter
solenoid) and is a very good one to use. If the GI newer type isn't
available, you can use the following suggestion and have satisfactory and
waterproof results.
For this, you will have to go back to NAPA again. You will want to get the
"Ford" style relay, stock number GPR 109. This relay is a different looking
round one and is a suitable replacement. Its footprint will match the two
mounting screws even though they don't look like they will. You will also
have to buy new brass nuts and washers for all the terminals because none
come with the NAPA relay. The nuts from the old relay will not fit the new
one because of the thread size differences. The cost is about $17 not
including the nuts. Connect the wires to the same physical terminals as the
correct assignment positions are similiar.
I find that about 55% of the part numbers in a CUCV TM are still
available from your local Chevy dealer (but may be upgraded) and this
concerns the glow plug controller card TEMPERATURE SENSOR in the upper rear
of the CUCV 6.2L engine:
GLOW PLUG TEMPERATURE SENSOR
Here is a real useful piece of info. The number in your 34P lists the Chevy
part number but it has been upgraded to this GM stock number: 10045847. It
comes with threadseal, shrink splice, and a little pigtail harness with plug
to splice into the black/yellow wires to replace the old harness connector
so it will fit the new glow plug system sensor. The white wires that come
with it are way too long so cut some length off so they won't be dangling
over the engine. Cost is about $22. This new upgraded kit is a perfect
replacement and don't use the old style sensor that may still be available
from gov't surplus.
I hope this helps all who read it and have a good day! Sincerely, Julian
Burke
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