From: Julian Burke (julian@knology.net)
Date: Sun Sep 25 2005 - 12:57:20 PDT
Well, I see it's time to get out my "Wash & Wear" answers to common CUCV
problems and questions that always pop up but have never read my articles
and postings!!
First question: "hile I have you all, here's another CUCV problem. What do
all of
you other CUCV folks do about a leaky cowl? Whenever it rains, the
water always comes in through the cowl vents. My floor isn't rusty
and I would like to keep it that way."
The answer is simple. All CUCV's leak commonly in two places, around the
top-front door gasket and inside the windshield wiper cowl. The roof drain
that ends at the front of the vehicle drops the water right in the door
gasket and pours to the floor. Replace the door gasket and you will also
have a tighter door fit.
Remove the wiper arms so that you can remove the cowl louver to gain access
inside the windshield cowl. Clean out all debris and wash out if possible.
When dry, caulk all bottom seams with RTV (silicone glue) and this will take
care of 99% of all leaks to the floor.
Second question: "I still don't understand how the system knows when to
turn off the glow plugs. Are the glow plugs heating air or water? If air,
what is telling system air is at right temp? What gauge in the dash? There
is no dash gauge in a CUCV other than the wait light."
The person who is asking this question doesn't understand a diesel or how it
works in the first place. It doesn't "know" when to turn off the glow plugs
other than it is only a timer to cycle the plugs. First understand that a
diesel engine runs on compression firing. A diesel engine typically has a
compression ratio of 22.5:1. This means that when the piston comes up to
the end of its' travel, it has squeezed/compressed all air in the chamber
almost 23 times. At this "violent" rate of sudden compression, the
temperature can be around 800-1500 degrees F. At this moment the injector
sprays (vaporizes in a diesel cloud) in a metered amount of diesel fuel.
This immediately ignites in this compressed atmosphere and forces the piston
down just like in a gasoline engine when spark plug ignites the gas. This
type of compressed ignition is powerful and causes that peculiar "diesel
noise" that all diesel engines have. Every brand of engine has its' own
"signature sound".
Now that you know how a diesel engine runs, I can now answer the
question. When most diesel engines are cranked (cold) to start them, they
have a little trouble building up temperature critical to initial ignition.
The larger the engine, the harder to start. There are two common ways to
start diesels (three of you include ether) but I will only concentrate on
the most common which is what CUCV's use. The GM 6.2 and the 6.5 liter
engines have a "precombustion" cup underneath the injector. If you have a
head removed, you will almost not see it because there is a cup/cover
pressed in flush with the head surface. It has a little slit in it about
1/4" X 3/8". If you pry this little cup out (about 1 1/2" in diameter) you
will then see this chamber. The injector is mounted (screwed in) at an
angle and the glow plug is mounted directed below it. The tip of the GLOW
PLUG is just barely in the path of the spray of the injector. Now bear in
mind that if you crank the engine long enough, you will build up temperature
to get the engine to fire but starters don't last that long so it needs a
little help from it's friend, Mr. glow plug. The glow plug turns on and the
tip of it will get red hot to about 1400-1600 degrees F. When this happens
the engine is cranked and the injector will do its' thing and atomize the
fuel and the spray touching the red hot tip of the plug will fire, thus
starting the engine. When engine is cold, most controllers will turn the
glow plugs back on for brief intervals to reduce excessive smoking in the
exhaust. Most diesel engines until warmed up a little will not have
complete combustion. BTW, there are no "quick start" glow plugs as such.
This is accomplished by putting a higher voltage on a glow plug to make it
heat up faster. If you put 24 volts on a 12 volt plug, it will heat up to
temperature in only a few seconds. This is how "quick start" systems
function. To answer this guy's question the glow plug doesn't heat up air
or water. ( How could it anyway?)
To answer the other question of how it knows when to heat up is simple:
There is a temperature sensor to tell the controller when to turn on. As a
matter of note here, when engine is above somewhere around 120 degrees F.,
engine will start on its' own without the help of the glow plugs. You will
notice the light on the dash will not come on when engine is warm or hot.
The engine will start on 3-4 glow plugs in moderate weather so you will not
notice glow plug failure until fall weather so it is a good idea to check
all glow plugs before fall.
I hope this answers these questions at hand. Julian Burke
This archive was generated by hypermail 2.1.4 : Fri Oct 28 2005 - 23:27:12 PDT