[Public-list] Why , oh, why won't my glow plugs glow?

[Bob Crinion]

While on the topic of Glow plugs,
I'll add my two cents worth.

Also does he have a glow plug fuse?
If there is approx 12 volts at the glow plugs then:

This is what my VW Diesel mechanic does, is measure the current going to the
glow plugs. Since all glow plugs are in parallel it is easy to isolate which
one is not working properly. A healthy glow plug draws several "AMPS" but
you need a fancy high current measuring device to check this.

Not to scientific a method, sometimes the mechanic takes out the glow plugs
and connects each one to a battery using battery cables and looks to see if
they glow well. You have to be careful they can get really hot but you can
easily see any difference from one good glow plug to a non glowing plug. If
one plug does not glow hot compared to another, it's the culprit. You could
also have more than one bad glow plug.

Sometimes diesels start OK with one bad glow plug in warm weather conditions
and it is not so noticeable until a second glow plug fails and the engine is
harder to start.

In all the years that I have diesels, it seems that I have to change a glow
plug every three to four years or so.

Never a problem with the glow plug solenoid.

I hope this may help.
-bob
#560

----Original Message-----
From: public-list-bounces at alberg30.org
[mailto:public-list-bounces at alberg30.org] On Behalf Of Mpete53 at aol.com
Sent: Wednesday, September 28, 2005 2:24 PM
To: public-list at alberg30.org
Subject: Re: [Public-list] Why , oh, why won't my glow plugs glow?

Randy
 
>From what I have read of your problem it sounds as if you are not getting  
power to the glow plugs or at most to little power. 
 
I find that using a volt meter to check for voltage drops is a handy  
diagnostic tool. A auto ranging digital meter is best but an analog meter
will  do.
 
As current passes through your electrical system any resistance will cause
a 
voltage across it. Ideally, the resistance is the item that you want to run,

IE: lights, pump, Glow plugs. If there is a unwanted resistance IE; a bad  
connection, a failing switch, there will be voltage drops. Since these
voltage  
drops are proportional to the current flowing through the wire, all the
tests  
must be done while under load. By checking for voltage drops where there 
should  not be one EI: the pos. post of the battery and the terminal on the 
starter  while cranking the engine, you can locate problems. In the example
of the  
starter, if there was a voltage reading retry with the test lead on the 
battery  cable clamp not the post. If this time there is no voltage, your
problem is 
 between the post and the clamp, dirty battery terminals. 
 
For your problem with the thing you distrust the solenoid. Set meter for  
reading volts DC and find a range that will go as high as 12 Volts. How
place 
your test leads to the terminals on the solenoid red one on the wire
leading 
from the pos. battery terminal and the black one on the terminal leading  to
the 
glow plug. (in general, when hooking up the meter leads, the red  test lead 
should be on the section of the circuit closer to the pos.  battery terminal

and the black lead should be the one further away on the  circuit) 
 
Now the test, when the switch for the glow plugs is off  you should  read 
battery voltage (about 12 volts) when the glow plugs are switched on  you
should 
read 0 volts. 
 
If the voltage goes to 0 your problem is not the solenoid. 
 
If the voltage is between 0 and a little less than 12 the solenoid should
be 
bad. 
 
If your voltage does not change, power is not going through the solenoid
BUT 
the solenoid might still be good. There may be a problem in  the circuit 
controlling the solenoid. If this is the case, check the power  activating
the 
solenoid. Connect the test leads to the wires leading from  the control
switch 
for the glow plugs. If you can find only one wire, most  likely the other 
connection is the case grounding to the block. This time  you are checking a
voltage 
across a load on a switch so the voltages we want to  see are reversed. 
Volts switched off 0 OK
Volts switched on 12, feed to solenoid OK so it looks like the solenoid is  
bad.
Volts switched on 11 or less not good. The circuit feeding the solenoid has

a problem
 
 Good luck
 
Mark
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