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  #1  
Old 02-02-2017, 06:14 PM
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Best Way to Test Glow Plugs?

Okay, looking for the best way to test glow plugs without pulling them out on my 92 300D. If I pull them I'm going to replace them, it has 310k miles on it. I was wondering if the method and readings I was getting is correct. I tested each plug with a multimeter set on the OHM setting and got 9-10 on all the plugs except one that read six ohms. is this right? Is there a better way to figure out which plugs are out? I'm getting cold start misfire and white smoke, just like glow plugs. There's a lack of cylinder heat on cold start. Once its warm, no smoke. The engine has good compression for its age, its well broken in.

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Old 02-02-2017, 06:49 PM
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Typically a glow plug either shows "open circuit", infinite resistance (bad) or a very low resistance for a good one. 6-9 ohms is high but I suspect your leads and connections all had resistance that added up. What do you see when connecting the leads together?
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Old 02-02-2017, 09:54 PM
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There is only 2 ways to test with the Glow Plugs still in the Engine. With the Ohm meter as you have doneor you can use an amp meter.
However, from what you said it sounds like you have one glow plug not up to snuff.

However, removing them and testing them on the Battery is the more definitive test. But, that does not meet your keeping them in the engine criteria.
If you look funola has some info on testing with an amp meter.

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If you remove them use a glow plug reamer or some alternative method to ream out the Carbon.

The Glow Plug in the pic was OK by the Ohm Meter but as you can see in the pic it is glowing in the middle and not the tip like it shoud so it is no good.
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Old 02-05-2017, 11:37 AM
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Originally Posted by Whiskeydan View Post
Typically a glow plug either shows "open circuit", infinite resistance (bad) or a very low resistance for a good one. 6-9 ohms is high but I suspect your leads and connections all had resistance that added up. What do you see when connecting the leads together?
Well, to be honest with ya I didn't try that. I'll have to see what I get next time. I think at this point though it's probably best to replace them all and ream the carbon. Who knows when its done?

Diesel911, thanks for the link a lot of good stuff in that post. I think that in my case, it's probably best to replace all the plugs. Do the wires ever need to be replaced at all? I'm also going to order a reamer. Would the reamer for the om602 work on my newer om606s? I have to do a glow plug on my 1999.
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Old 02-05-2017, 01:10 PM
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If want to do a quick check to see if you actually have a dead glow plug, you could unplug the glow plug harness at the relay and use a test light hooked to your battery at each pin of the harness connector. If there is no light, then it's definitely bad. If the light goes on, the glow plug is generally working. Now I say "generally" because you really need to check the resistance or physically see it hooked to battery power as D-911 suggested to see if it's truly good. But in my experience 9 times out of 10 if the light is on, the plug is good.


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Old 02-05-2017, 04:25 PM
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Quote:
Originally Posted by jake12tech
Would the reamer for the om602 work on my newer om606s? I have to do a glow plug on my 1999.
Nope. Look up the differences between the glow plugs on the 602/3 and the 606 and you'll understand why. If you're replacing a glow plug on the 606, have a poke around the forum on how to do it, they can jam up and break off in the head!
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Old 02-05-2017, 05:24 PM
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Originally Posted by Diseasel300 View Post
Nope. Look up the differences between the glow plugs on the 602/3 and the 606 and you'll understand why. If you're replacing a glow plug on the 606, have a poke around the forum on how to do it, they can jam up and break off in the head!
Good to know. Oh believe me, I've been researching and I dread it like the Bubonic Plague. I don't know what my best option is. I've read that soaking them in PB and using a torque wrench to remove it is my best option. Plus, patience.

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Originally Posted by DeliveryValve View Post
If want to do a quick check to see if you actually have a dead glow plug, you could unplug the glow plug harness at the relay and use a test light hooked to your battery at each pin of the harness connector. If there is no light, then it's definitely bad. If the light goes on, the glow plug is generally working. Now I say "generally" because you really need to check the resistance or physically see it hooked to battery power as D-911 suggested to see if it's truly good. But in my experience 9 times out of 10 if the light is on, the plug is good.


.
Next time I'm over where the car is at, I'll have to take a look and see what I find out. I knew I should have bought that $7.00 test light when I was just at Sears.
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Old 02-06-2017, 08:33 AM
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Originally Posted by Diesel911 View Post
The Glow Plug in the pic was OK by the Ohm Meter but as you can see in the pic it is glowing in the middle and not the tip like it shoud so it is no good.
Great example!!!

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Old 02-06-2017, 09:28 AM
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Jake - are you sure? The directions on my torque wrench say it cannot be used to remove bolts.
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Old 02-06-2017, 09:36 AM
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If I worry about a stuck glow plug, I'd use an air or electric impact gun on a low torque setting rather than a hand ratchet unless it is a T-bar so as to not impart any "bending" action on the glow plug. I'd slowly loosen/ tighten the glow plug while adding penetrating oil until the glow plug is fully un-threaded. The impact action really helps with stuck and rusted threads.
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Old 02-06-2017, 11:47 AM
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Originally Posted by Diesel911 View Post

The Glow Plug in the pic was OK by the Ohm Meter but as you can see in the pic it is glowing in the middle and not the tip like it shoud so it is no good.
Really? Send it to me and I would use them anytime. I go by the small resistance value and it has never fail me. You have 4 to 6 gp just replace the one with resistance out of line with the rest. You can't go wrong.
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Old 02-24-2017, 02:17 PM
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Really? Send it to me and I would use them anytime. I go by the small resistance value and it has never fail me. You have 4 to 6 gp just replace the one with resistance out of line with the rest. You can't go wrong.
Some of us in colder climates need glow plugs that are glowing correctly!

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