Testing Glow Plugs

doghead

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Yes, that may be your issue.
 

Barrman

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When putting power to glow plugs that are out of an engine like Karl did. Please put on safety glasses. I have had a few go "POP!" as soon as I put power to them. Little bits of hot metal go flying when this happens.

Why put power to them? I wanted to see why it was only pulling .8 Ohms, or whatever resistance I got. Sometimes just the tip lights up. Other times just the base. They stay hot for a pretty long time after you put power to them as well. Just a simple word of warning.
 

jatonka

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my CUCV plow truck is starting hard again, I installed AC 13G glow plugs 3 years ago and it has been great until now. I picked up 8 new 13G glow plugs today for $10.59 each, will install Friday and post back here how we're doing. I will test the old ones and see how many failed. JT out
 

antennaclimber

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The M1009 seems to be a little hard to start in very cold temperatures. Excessive cranking time and lots of smoke on start up. I was wondering if I had a a few inoperative glow plugs.

Ohm tested all 8 glow plugs and found 3 to be completely open. The remaining ones measured out at .8 ohms each.

I had a box of 8 fresh AC13G plugs here, changed out all of them. I figured that it's just a matter of time until the others fail. Might as well change all 8 to be sure that all of them are functioning properly.
 

jatonka

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A little off topic but still on CUCV glow plug system. Is there a way to test the resistance of the double resistor that cuts 24v down to 12v to fire the glow plugs? I removed mine and wired from the front battery through a 100 amp breaker to the glow plug solenoid and I'm not happy with the results. Have new 13g glow plugs installed. Takes a long time to heat them up and sometimes the GP solenoid doesn't kick out until minutes after the truck starts. Really hard on the front battery and alternator #1. JT
 

MarcusOReallyus

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A little off topic but still on CUCV glow plug system. Is there a way to test the resistance of the double resistor that cuts 24v down to 12v to fire the glow plugs?
Yep. Just use an ohmmeter. Do not have the resistors connected to the batteries when you test it. You'll need a good quality ohmmeter.
 

jatonka

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Karl, as always, thank you. I had tried an ohm meter earlier, thought I needed 6 ohms and got confused. If you are coming to Redball meet at MT Bethel, PA this weekend, can you bring your ohm meter and I will bring resistors down. JT
 

antennaclimber

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Karl, as always, thank you. I had tried an ohm meter earlier, thought I needed 6 ohms and got confused. If you are coming to Redball meet at MT Bethel, PA this weekend, can you bring your ohm meter and I will bring resistors down. JT
Unfortunately I will not be going to the Redball meet this weekend.

Put an ohm meter on it and see what the reading is. Then see what the ohm meter reads by touching the leads together, subtract that amount from the resistor reading. The difference will be the value of the resistor pack. It will be a low value, some meters do not have enough resolution and will not be able to give an accurate reading.

There is not much to go wrong with the resistors. They are a wire wound high power resistor that can dissipate a considerable amount of heat. I would venture to guess that if they go bad, they will go to a high resistance or open. It's basically a heater element dropping the 24 volts down to 12 for the GP's.
 

319cssb

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I have replaced the bad glow plugs on the M1009 two months ago. and today I checked one for giggles and laughs. the first one was OL the second had 3 ohm resistance. The resistor pack is supposed to cut 24V down to 12v, correct?
So if the resistor pack is bad it will give the G60 glow plugs 24v and they soon start to fail? Or will they just glow for a shorter period of time?
If they do fail prematurely, what if I use HMMWV glow plugs? They are 24V, I believe. Gotta change the connector too then.
 

MarcusOReallyus

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In general, resistors fail by opening, rather than by shorting. That is, they don't pass any current at all. If one of them fails, you'll get LOWER voltage to the resistors. If they both fail, you get nothing.

With the resistors in place, if one of your GPs goes bad, the rest of them see a higher voltage, which makes them burn out a bit faster. Then another one goes, and the voltage goes up again, making the next one fail even faster, and so on. This is what is known as a "cascade failure", and it's the reason that many CUCV owners bypass the resistor pack and feed 12v from the front battery. No more cascade failure. This has the downside of putting an unequal load on the batteries, but that seems to be more of a theoretical consideration than a real problem.

Some prefer it stock, and do fine with it. If you can spot the signs of a bad GP early, and get it replaced quickly, you can avoid the cascade failure that way.
 

rmesgt

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Yep. Just use an ohmmeter. Do not have the resistors connected to the batteries when you test it. You'll need a good quality ohmmeter.
I would like to test my resistors, but I am unsure as to how to accomplish this. I have several multi-meters, but that doesn't mean I am well versed as to how to use them. There are many settings on each meter and I don't know what they all do. If I understand this thread correctly, I should disconnect the resistor pack from the 24V buss bar on passenger side fire wall. Set my meter to "Ohms", then put a probe on each end of one resistor (the top resistor, for example). My meter should give a value that indicates the resistance between the probes. is this correct? Please advise....
 

MarcusOReallyus

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I would like to test my resistors, but I am unsure as to how to accomplish this. I have several multi-meters, but that doesn't mean I am well versed as to how to use them. There are many settings on each meter and I don't know what they all do. If I understand this thread correctly, I should disconnect the resistor pack from the 24V buss bar on passenger side fire wall. Set my meter to "Ohms", then put a probe on each end of one resistor (the top resistor, for example). My meter should give a value that indicates the resistance between the probes. is this correct? Please advise....

If you are testing the resistor pack, yes, disconnect it from the 24v buss bar and from the GP relay. Measure the resistance from one side of the resistor pack to the other. One probe on each end. The resistors are connected in parallel. You measure both at the same time, not individually.

In theory, you should measure only the resistor pack, not the leads going to and from the resistor pack. If you can reach the point where the lead connects to the resistor, do that. If not, measure from the 24v lead (once its disconnected) where it would normally connect to the buss bar, and to the other lead's end where it connects to the GP relay. If it's all good, that should be close enough. If the reading isn't correct, you'll need to make the effort to measure only the resistor pack without the leads in order to find where the problem is. There could be a poor connection in one of the leads, for example. Corrosion creates resistance. If the resistance anywhere on that path from the 24v buss bar to the GP is higher than normal, you'll get less voltage at the GP, meaning it won't get as hot as it should.


To test the GPs, there is no need to mess with the resistor pack. Just measure each GP individually:

  1. Disconnect the GP connector at the GP. This is a straight pull away from the GP.
  2. Connect one probe of your meter to a good ground location. The intake manifold, for example. Make sure you have a solid, clean connection.
  3. Touch the tip of the other probe to the tip of the GP where the wire normally connects.
  4. Read the meter.
  5. Write down your reading.
  6. Reconnect that GP.
  7. Repeat for each of the GPs.
 
Last edited:

rmesgt

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If you are testing the resistor pack, yes, disconnect it from the 24v buss bar and from the GP relay. Measure the resistance from one side of the resistor pack to the other. One probe on each end. The resistors are connected in parallel. You measure both at the same time, not individually.

In theory, you should measure only the resistor pack, not the leads going to and from the resistor pack. If you can reach the point where the lead connects to the resistor, do that. If not, measure from the 24v lead (once its disconnected) where it would normally connect to the buss bar, and to the other lead's end where it connects to the GP relay. If it's all good, that should be close enough. If the reading isn't correct, you'll need to make the effort to measure only the resistor pack without the leads in order to find where the problem is. There could be a poor connection in one of the leads, for example. Corrosion creates resistance. If the resistance anywhere on that path from the 24v buss bar to the GP is higher than normal, you'll get less voltage at the GP, meaning it won't get as hot as it should.


To test the GPs, there is no need to mess with the resistor pack. Just measure each GP individually:

  1. Disconnect the GP connector at the GP. This is a straight pull away from the GP.
  2. Connect one probe of your meter to a good ground location. The intake manifold, for example. Make sure you have a solid, clean connection.
  3. Touch the tip of the other probe to the tip of the GP where the wire normally connects.
  4. Read the meter.
  5. Write down your reading.
  6. Reconnect that GP.
  7. Repeat for each of the GPs.
Thank you sir!!!! I have copied this information and I put it in my binder. I wonder if I should take the time to test my new glow plugs. Once I put the new plugs in, my truck fired right up. I have begun to realize that I am my CUCV's worst enemy. All this time I thought I was doing everything right, but I still manage to kill my truck and blazer.
 
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