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Discussion Starter · #1 · (Edited)
Is it common to see glow plug resistance readings at the valve cover gasket connector between 11 and 32 ohms? Are these typical failures? I've been digging through forums for days and this seems like the best forum, but I still don't see what I'm looking for. I want to understand glow plug failure. I want to know how glow plug resistance changes as they wear out over time.

I have readings of 11 ohms on cylinders 1,3,5,7
and 32 ohms on cylinders 2,4,6
and open (infinite) reading on cylinder 8

Every post I see says over 2 ohms is bad, but none of them talk about what values are commonly seen when measuring from the valve cover connector to the negative post of the battery. Cylinder 8 being open makes sense to me as being burnt out. All the other measurements don't make sense to me, because I have never seen any other posts with resistance readings mentioned like these readings.

Can anyone explain how glow plug resistance should read over the life of a glow plug? Does resistance increase until the plug finally burns out? Do I have 7 worn out plugs and one completely dead plug? Is this common? Does this sound normal for a truck with 250K miles? Thanks for your help!
 

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I have not heard of resistance readings that you indicate except #8 at "0".
A "0" reading indicates a bad GP when the ohmmeter functions correctly.
It is not typical for several GP to have identical values.
Where are you holding the red & black leads?
Do you often use your ohmmeter? Are you confident it is set up properly?

Thanks
 

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Discussion Starter · #3 · (Edited)
I'm an experienced multi-meter user and an experienced troubleshooter. I am also a diesel newbie. The negative battery cable connections on the block have been taken apart, cleaned up, and reinstalled, the battery terminals are brand new, and the batteries are also new. I tried using the negative post on the left battery, right battery, and various places on the engine as grounds and got the same results within an ohm or two. I'm a little puzzled at this point. I did not expect to see these sorts of numbers. I expected 0-2 ohms or open. I did not try another meter yet, but I can do that.
 

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I'm an experienced multi-meter user and an experienced troubleshooter. I am also a diesel newbie. The negative battery cable connections on the block have been taken apart, cleaned up, and reinstalled, the battery terminals are brand new, and the batteries are also new. I tried using the negative post on the left battery, right battery, and various places on the engine as grounds and got the same results within an ohm or two. I'm a little puzzled at this point. I did not expect to see these sorts of numbers. I expected 0-2 ohms or open. I did not try another meter yet, but I can do that.
I usually find a ground point near the UVCH and just to confirm you are testing the 2 "outboard" pins on either end of the 9-pin connector at the VC.

It sounds like you have been pro-active in your battery maintenance. Are you just being pro-active with your GP or are you having cold start issues that makes you think the GP are bad?

Cheers
 

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I see them in the 30s on a regular basis. They are shot if verified at the glow plug right before pulling out to pitch. This verifies if it's not the under cover harness.
Thanks for stepping in Nick.

So that would mean his GP have all "aged" very consistently and are all ready to be replaced?
 

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Sometimes I find one with a dead short. My theory there is that the center element burns or breaks and then touches the side of the inside of the glow plug.
This will eventually fry the harness, pins and or seriously erode the plunger in the glow plug relay.
 

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Discussion Starter · #9 ·
You people -- this forum -- you are so awesome!! Maryland Dieselnick!! You are fantastic. You are the first person ever to mention that glow plugs die around 30 ohms and I have scoured the web for days and days. I am having cold start issues like crazy. I'm not opposed to doing good proactive general maintenance, but in this case I am trying to solve a terrible cold starting problem, but I didn't really want to confuse the issue, because I really wanted to understand how glow plugs die over time, and I figured if I mentioned cold start issues, that would have driven this thread in many diverse directions.

So I'm going to replace the glow plugs and take it from there. The connectors need love too and will see a new one or two. The previous owner was not aware of the concept of maintenance, but the price was good.

Thanks a million, I really really needed someone to say that a glow plug in the 30s of ohms was a common death reading. Cool.
 

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Glow plugs should be considered BAD if they measure anything outside of 0.6 and 2 ohms.
 

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You people -- this forum -- you are so awesome!! Maryland Dieselnick!! You are fantastic. You are the first person ever to mention that glow plugs die around 30 ohms and I have scoured the web for days and days. I am having cold start issues like crazy. I'm not opposed to doing good proactive general maintenance, but in this case I am trying to solve a terrible cold starting problem, but I didn't really want to confuse the issue, because I really wanted to understand how glow plugs die over time, and I figured if I mentioned cold start issues, that would have driven this thread in many diverse directions.

So I'm going to replace the glow plugs and take it from there. The connectors need love too and will see a new one or two. The previous owner was not aware of the concept of maintenance, but the price was good.

Thanks a million, I really really needed someone to say that a glow plug in the 30s of ohms was a common death reading. Cool.
When you get the old GPs out, would you test a couple and see if the resistance is identical?

Are you plugging it in at night now to help you with that cold morning start? As long as you have your multi-meter handy, you might want to check the resistance across the prongs of your block heater plug. It should read 14-15 Ohms. The cords have a habit of getting a short.
 

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For clarification I'm not saying they die around the 30s. I'm saying I find them there. They are technically failing at a reading of 6 or 7 and over time maybe they got into the 30s. I do not know if that's the case or one day it jumped straight into the 30s. I see them between single digits on up into the 30s.
I also stress that you start at the valve covers to take the harness into account. Then disconnect at glowplug and test at it.
 

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A glow plug that measures 30 ohms is still going to heat up. I would hate to have it in my hand and try to hold onto it if it was connected to a battery. But we expect for them to warm up a small chamber on a cold piece of cast metal and we expect them to do it fairly fast. This is where one that is measuring out of the range I indicated would be causing problems.
 

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Well you just had to pick a night it's in the teens to go and do a heat up on a 30s ohm glow. Plug. I'm worried out jumper wires on this test of the correct gauge being in my hands before the element but we are going to find out just not tonight.lol
 

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You could always come over to my house. It is suppose to get down to a -10 or so.

And Wednesday I'll need to fire up the old truck. It hasn't been ran for 2 weeks now and is sitting in a cold garage.
 

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Man every notice how thing change at different ranges? The teens are the first tier down from the 32 mark. Then things are another tier and then you hit the zero to minus ten and then it's another tier. Each tier has its own characteristics.

Ok on commercial I'm gettin a plug, jump box and temp gun and I can count. I not hunting wire and matching gauges tonight to see how you can see the effects there.
 

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Discussion Starter · #17 ·
Maryland Dieselnick --

I think I understand what you're saying. Glow plugs increase in resistance from the time they are new until the time they are useless because they don't get hot enough. For example, a glow plug at 5-7 ohms may still work a little bit, but it is considered to be faulty because it does not produce enough heat to significantly help start the engine. Unless the GPs short or open at some point, you could expect to see resistance values in the teens and 30s on old glow plugs. Sometimes the harness is at fault and the glow plug is OK.

Given the readings I took on my truck, and what I know of its prior lack of maintenance, I bet the odd bank GPs were replaced together some time ago and the even side GPs are original.

Am I on track here in my thinking?
 

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Discussion Starter · #18 ·
Arctic Driver -- I just noticed you're in Longmont! I was out there many years ago. I have never seen more heavy duty work trucks for sale in one place! Ever! I was shocked and amazed, heavy duty trucks for sale at every little car lot in town, just like heaven to me. Is it still that way? Why?
 

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Isn't it still pretty strange to have an identical 11 Ohms on one whole bank 1,3,5,7 ?

Do GPs really age that consistently with one another?

Even when I take brand new ones out of the package, they don't have equal Ohms to the each other.

Could an equal resistance be an indication of a faulty harness?
 
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