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  #1  
Old 10-25-2005, 12:17 AM
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Testing glowplugs correctly?

Hey,
I know there are a few threads on the subject and have read them(mostly older cars), I guess my question may have to do with how to use a volt/ohm meter. I've got the anolog with the needle. I first switch the dial to ohms 1x, then touch the two leads together and set the needle to zero. I then put the negative end to the threads of the GP and the positive end I touch to the electrical end of the GP. I have done the above and there is no movement of the needle. The car starts fine and the light comes on and then goes out(of course I live in sunny So.CA). I'm I doing this right and need to replace all the plugs? They've never been replaced and the car has 140k.
Thanks,
Matt


Last edited by 96E300D; 10-25-2005 at 01:10 PM.
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  #2  
Old 10-25-2005, 07:59 AM
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Quote:
Originally Posted by 96E300D
...I guess my question may have to do with how to use a volt/ohm meter. I've got the anolog with the needle. I first switch the dial to ohms 1x, then touch the two leads together and set the needle to zero...
Good, this calibrates the meter and proves it will work.
Quote:
...I then put the negative end to the threads of the GP and the positive end I touch to the electrical end of the GP. I have done the above and there is no movement of the needle...
There may be non-conductive a film on the end of the plug that you did not break through and thus got no reading. Your method is OK.

You can also clamp the negative to bare metal on the engine, and touch either the glow plug post, or disconnect the wiring harness at the relay and touch each socket in turn.

Let us know how this works.
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  #3  
Old 10-25-2005, 12:52 PM
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All the plugs are out due to the fact the head is at the machine shop, so I would need to re-connect them to the harness. However, I mis-spoke when I said the needle didn't move. The needle does move, it just goes from one end of the scale to zero. Bad Plugs or should I connect them to the harness and try that?
Matt
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  #4  
Old 10-25-2005, 01:13 PM
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Quote:
Originally Posted by 96E300D
...The needle does move, it just goes from one end of the scale to zero. Bad Plugs or should I connect them to the harness and try that?
Matt
OK, now I understand more.

Well, just to be sure, one lead should be on the larger threads on the end that goes into the cylinder, and the other lead on the small stud that the wire connects to.

Your meter scale might be too high. I would expect a zero reading on a 1000 ohm scale. It would be hard to see the difference between zero ohms, which would move the needle 1000/1000 units, or full-scale, and 1 ohm that would move it 999/1000 units.

You said you set the scale to 1x. Is this ohms, or 'kilo-ohms' which is 1,000 ohms full scale?

This is hard, since I can't see your meter... What meter are you using?
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  #5  
Old 10-25-2005, 03:14 PM
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Hi Jim,
Thanks for taking the time to work through this with me. On the ohm scale, it starts at 0 and goes to 5k(zero on the right side of the scale). When I set the dial to Rx1, instead of going all the way to zero it stops at about one.
Matt
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  #6  
Old 10-25-2005, 06:15 PM
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found a RS digital multi-tester, so, set at 200(choices are 200, 2k, 20k, 200k and 2m) the readings are 00.8. Good/bad news?
Matt
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  #7  
Old 10-25-2005, 08:24 PM
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Quote:
Originally Posted by 96E300D
...On the ohm scale, it starts at 0 and goes to 5k(zero on the right side of the scale). When I set the dial to Rx1, instead of going all the way to zero it stops at about one.
When a dial-type ohmmeter won't zero, it usually means a weak battery.
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  #8  
Old 10-25-2005, 08:24 PM
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Quote:
Originally Posted by 96E300D
found a RS digital multi-tester, so, set at 200(choices are 200, 2k, 20k, 200k and 2m) the readings are 00.8. Good/bad news?
Matt
That sounds like 0.8 ohms, which is less than 1.0, which should be 'golden.'
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  #9  
Old 10-25-2005, 09:31 PM
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Thanks again Jim! Now after all that, does it make any sense to replace the GP's based on their age while everythings apart? Is there a typical life expectancy on these and am I close to it at 140K?
Just a thought.
Matt
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  #10  
Old 10-25-2005, 10:01 PM
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Quote:
Originally Posted by 96E300D
...Now after all that, does it make any sense to replace the GP's based on their age while everythings apart? Is there a typical life expectancy on these and am I close to it at 140K?
You will find two 'schools of thought' here...

"Replace 'em, it's cheap insurance."

"If it ain't broke, don't fix it."

I tend not to replace stuff until it's broken, or beyond.
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  #11  
Old 10-25-2005, 11:41 PM
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Yeah, I'll probably have close to a grand in machine work and parts for the head repair, so saving an extra hundred will help. Thanks again.
Matt
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  #12  
Old 10-26-2005, 07:33 AM
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I remove them and put 12vdc accross them. If they light up on the ends then they are good.
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Jim
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  #13  
Old 10-26-2005, 03:04 PM
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Well, for fun and giggles, and to verify my previous testing, I hooked up the GP's to my battery. Within 6 sec., all lit up beautifully.
Matt

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