There are two failure modes for pencil type glow plugs. Well, three
really.
One, the filament breaks (no continuity) and fails to heat.
Two, the filament sags and contact the side of the "pencil". Lower
resistance, heats but not at the tip, won't fire the fuel mist.
Three, the resistance of the filament goes so high it won't heat.
Occasionally the filament to pencil weld at the tip will fail,
allowing the filament to fall down and short, yielding failure #2.
Champion plugs, which are intended to be used in switching mode power
(50% duty cycle typically) and therefore average 6V instead of 12V
across the plugs are well known for weld failure in constant 12V
systems. Had all six fail rather rapidly on the Volvo TD, all with a
nice neat hole in the tip. Some of them still worked reasonably
well, but not well enough to fire. Repeated start attempts will cook
them very rapidly. The Bosch or Beru plugs are designed for constant
12V use and do not fail at the tip weld like that.
Champions will work fine so long as the engine starts instantly and
you short cycle them (crank as soon as the lamp goes out). Hard
starts or repeated glows will kill them right off in my experience.
Peter
On Oct 29, 2011, at 8:37 PM, Allan Streib wrote:
Michael Canfield <slozuk...@gmail.com> writes:
I just checked out my glow plugs and got 3.9-4.4ohms on 3 of them and
nothing on two. Replaced the two that read nothing and everything
is back
to normal. I was taking a reading from the plug body to the tip
with the
harness connected. Forgot to unplug the harness this time. So
the higher
reading was showing that 3 were still good but not actually
getting an
exact reading for each one? I was looking more for continuity
than an
exact reading anyway.
The plugs can (and typically do in my experience) "fail" without being
totally burned out (open circuit). They just don't get hot enough
anymore.
Sounds like you fixed your problem though.
Allan
--
1983 300D
1979 300SD
_______________________________________
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
_______________________________________
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
