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Tractor Talk Discussion Forum

How to check glow plugs

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Jaker

12-02-2004 09:22:22




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I have a small kubota engine that I think the glow plugs need repolaced in. Is there a way to ckeck them without taking them out and replaceing them? THe reason I feel they need replaced is when I start the engine one cylinder won't fire unless I hold the key on. I would think they could be checked with an ohm meter if I only knew how. thanks Jake




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Larry806

12-02-2004 17:13:31




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 Re: How to check glow plugs in reply to Jaker, 12-02-2004 09:22:22  
We just clip the test light to a + , unhook the wire to glow plug When you touch the point of the testlight to where the wire goes on if it lights its good, bad no light



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Allan in NE

12-02-2004 19:00:58




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 Re: How to check glow plugs in reply to Larry806, 12-02-2004 17:13:31  
Atta Boy Larry!

This 'fast and dirty' test light check will catch 99% of the bad glow plugs.

Forget the silly ohmeter.

Allan



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Bob

12-02-2004 20:51:07




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 Re: How to check glow plugs in reply to Allan in NE, 12-02-2004 19:00:58  
The ammeter test I mentioned before is still something to consider, though, as you can compare the draw of all the glow plugs individually, and replace any weak one.

Usually, they fail completely, but from time to time, they will still show good with a test light, but draw a lot less current than they should. This makes for poor starting, and lots of smoke and misfire until the cylinder warms up.

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Ramrod

12-02-2004 14:00:03




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 Re: How to check glow plugs in reply to Jaker, 12-02-2004 09:22:22  
Sure, your ohmeter will check them for you! They will look like a short if they are good, and open if they are bad. Just disconnect the wire(s) to the glow plug(s) first. You could also take your test light used to check for hot circuits and use it backwards to check them. Just hook the ground clip to battery Positive (+) terminal, and when you touch ground with the probe, the light will come on. Again, disconnect the glow plug wire(s) and touch the probe to the glow plug contact. If it is good, the light will come on. One disclaimer... if your test light is a solid state diode light, you may have to reverse the leads to get a light.

Ramrod

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kraigWY

12-02-2004 10:09:56




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 Re: How to check glow plugs in reply to Jaker, 12-02-2004 09:22:22  
First test the electrical connections the bank of glow plugs to see if they really needed to be replaced. Start by grounding a test meter negative 200 ohms selection on the test meter and pulled the glow plug connectors wire loom apart. Touching each connector inside we either got a “NO” read (bad plug) or a value on the meter of .5 or so showing a “GOOD” glow plug.



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Bob

12-02-2004 09:55:02




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 Re: How to check glow plugs in reply to Jaker, 12-02-2004 09:22:22  
They will show REALLY LOW resistance with an Ohmmeter, if good. The trouble is, most common meters are not real good at reading low Ohms values accurately.

I would think they would read less than a couple of Ohms, or perhaps even less than an Ohm. You could check the value of a new one, or known-good one, and compare that to the others.

To check glow plugs, I use an Ammeter capable of reading 60 Amps. Connect the (+) side the ammeter to the (+) battery terminal, and, (after unhooking all the glow plugs from the wiring), momentarily touch the (-) lead from the test Ammeter to each glow plug one at a time, and note the Amp draw of each glow plug.

DO NOT power up a glow plug for more than a second or two, as they may be damaged and break, causing engine damage, since you are feeding power direct, and the controller is not in the circuit to protect them.

I don't know what the Amperage draw of your specific glow plugs should be. Typically, diesel glow plugs draw from 10 Amps to 30 amps each, depending on the specific application, and, for a specific application, the Amperage draw will be very close between all the cylinders.

Since you are having trouble with one cylinder, you can compare the Ohms reading, or the Amperage draw of that glow plug to the others, and any substantial differance will indicate a bad glow plug.

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