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  #46  
Old 07-29-2007, 01:45 AM
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Quote:
Originally Posted by funola View Post
A good way to test glow plugs without removing them is to apply +12 power through an ampmeter to each wire in the the glow plug relay plug/ harness (after unplugging it). Make sure each one is drawing the same current (approx 20 amps).
Who's got an ammeter that can handle 20A DC............lying around??

Wish I did..........
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  #47  
Old 07-29-2007, 01:46 AM
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Originally Posted by Brian Carlton View Post
It's a bit more complex than you mentioned simply because of the separate wiring for #1. When #1 goes out, you always lose the light. If any of the other four go out, you do not lose the light. AFAIK, you'll need to lose two plugs 2-5 for the light to extinguish. I can vouch for the fact that the light works perfectly when #5 has failed.

That's good to know. Does #1 glow plug have a higher probability of burning out?
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  #48  
Old 07-29-2007, 01:46 AM
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Originally Posted by funola View Post
That's good to know. Does #1 glow plug have a higher probability of burning out?
I don't see why it would...........?
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  #49  
Old 07-29-2007, 01:51 AM
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Murphy says that the most difficult one to reach will always have the highest probability of burning out.
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  #50  
Old 07-29-2007, 01:52 AM
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I do. I have 3 of them. Go to Sears and buy their DVM with thermocouple input which has a 20A range. I paid $30 for ea. but price may have gone up a bit. If you don't have a 20 A amp meter, and you have a battery charger with higher than 20A capacity, use that to drive the glow plug and watch the meter on the charger.

Quote:
Originally Posted by Brian Carlton View Post
Who's got an ammeter that can handle 20A DC............lying around??

Wish I did..........
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  #51  
Old 07-29-2007, 01:53 AM
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I don't see why it would...........?
I didn't think so either. Just that in this post, many have reported #1 glow plug burned out.
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  #52  
Old 07-29-2007, 01:58 AM
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I do. I have 3 of them. Go to Sears and buy their DVM with thermocouple input which has a 20A range. I paid $30 for ea. but price may have gone up a bit. If you don't have a 20 A amp meter, and you have a battery charger with higher than 20A capacity, use that to drive the glow plug and watch the meter on the charger.
I've got a very good analog meter from Radio Shack but it only handles 10A.

Probably can't justify another $50 meter once every five years when I'd like to measure 20A. Besides, I'd put that meter in unobtainville and it would be useless anyway.
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  #53  
Old 07-29-2007, 01:58 AM
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Another trick is wrap the side of the nut in paper or plastic and shove in the socket.

This is the method I use to secure the glow plug nut in the socket. If the paper or plastic is thick enough, that nut won't fall out on ya.
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  #54  
Old 07-29-2007, 02:05 AM
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Then get a starter motor clamp on ampmeter. They are cheap. mine is made by Black Hawk. I have not seen them in local auto parts stores but I think JC Whitney has them. I put it in proximity of the wire (no need to break the circuit) that feeds all the glow plugs and put a mark where the needle registers. If it reads lower than that mark, then one or more glow plug is toast, so I move the clamp amp to the individual glow plug wire to find the bad one. Works great! saves time.

Quote:
Originally Posted by Brian Carlton View Post
I've got a very good analog meter from Radio Shack but it only handles 10A.

Probably can't justify another $50 meter once every five years when I'd like to measure 20A. Besides, I'd put that meter in unobtainville and it would be useless anyway.
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  #55  
Old 07-29-2007, 02:44 AM
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Hi. Uh. Lots of messages, I see.

Let me ask you this, .. It seems like everyone on this forum who has the "same" problem as me has a working relay that clicks whenever they turn the key to pre-glow. Is this not true?

Then how are we all even talking about the same thing? I don't hear anything during pre-glow and yet it still starts smoothly. My problem is not the same as Brian's for example because the relay socket for his first GP didn't have a good reading. Right now for me all the sockets are reading fine. It's odd that this issue isn't shared by anyone else.
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  #56  
Old 07-29-2007, 02:47 AM
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Also how does the ampmeter/ammeter help? If you know the resistance going into the plug by doing the probe-in-the-relay-plug check, and if you know there's exactly battery voltage going into that plug by doing the probe-on-the-pin check, then isn't it clear that you're getting V/R amperes into the plug? How is this check any different?
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  #57  
Old 07-29-2007, 10:06 AM
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Solo,

Several months ago when I acquired my 84 300TD turbo it had the same problem you describe. No GP dash light, smooth start, all plugs read 0.6 Ohms with a good multimeter. I had to remove each glowplug and test it on the battery (as I already described).

You've verified that the dash light bulb is functional right? If I remember correctly, the GP dash light would work (and time out) on mine when I disconnected the wiring harness at the GP relay.

If you had several GPs out (more than 2) your cold engine start would be noticeably rough. But with only 1 GP out, you might not really notice. And, only GP #1 will cause the light not to work by itself. So start there. Pull the wiring harness (the one that goes to the GPs) off the GP relay and see if the dash light works. If it does, then remove GP #1 and test that it glows red hot on the battery. If not, replace it.

I would probably pull and test all the GPs as well.
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  #58  
Old 07-29-2007, 10:47 AM
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Quote:
Originally Posted by funola View Post
This is the method I use to secure the glow plug nut in the socket. If the paper or plastic is thick enough, that nut won't fall out on ya.
Yep, got to give that a whirl next time. Thanks.

Might even get one of those clamp on ammeters as well.
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  #59  
Old 07-29-2007, 12:07 PM
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That is a good question. When you are testing with an ohm meter, you are not testing under actual operating condition where an ammeter is (almost). A glow plug gets hot, if not perfect, internal connections can open up (like a thermostat) as it heats up and not glow anymore. This is rare but could happen, especially to ones where the center electrode has spun. Such a glow plug could test good per an ohmmeter but still be bad.
Quote:
Originally Posted by solostyle View Post
Also how does the ampmeter/ammeter help? If you know the resistance going into the plug by doing the probe-in-the-relay-plug check, and if you know there's exactly battery voltage going into that plug by doing the probe-on-the-pin check, then isn't it clear that you're getting V/R amperes into the plug? How is this check any different?
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  #60  
Old 07-29-2007, 12:25 PM
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Here's a pic of the Starter/generator ammeter on the main +12 V feed to a 240D glow plug relay.

Note: These type of ammeters are not designed to be very accurate in absolute terms. You have to understand its limitations and use it as such. It is not really a "clamp amp" where the meter acts as the secondary of a transformer (which works on AC current only). I believe it works on magnetism. While I have not taken one apart, I think it is very simple and is all mechanical, no coils etc.




Quote:
Originally Posted by Brian Carlton View Post
Yep, got to give that a whirl next time. Thanks.

Might even get one of those clamp on ammeters as well.
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