Another glow plug question..

[MT2501owner]

Tractor has become harder to start.
Glow plug indicator on the dash no longer glows or gets hot, but the resistor behind the dash dang sure does.
Gave it a solid 20 seconds on the key switch and then noticed a bit of smoke coming from behind the dash.
What is this telling me ? Something is drawing amps right ?
Tractor is at a weekend location and just trying to put a plan together for this weekend when I can get back on it.
This is an 87 model Mitsubishi MT2501 (grey market) but parts are available.

 

[RPW]

Glow plug(s) shorted out or short in wiring. Disconnect wire at glow plug and using a multimeter check for a 0 ohm reading. If 0 then plug is bad. If other then disconnect all plugs and check for 12 volts from wire to ground. If no or low voltage then suspect short in wire.

 

[otlski]

Be sure to use your lowest range (the most sensitive range) on your ohmmeter. The difference between a good plug and a bad one is a few ohms.

 

[Jerry/MT]

Glow plug(s) shorted out or short in wiring. Disconnect wire at glow plug and using a multimeter check for a 0 ohm reading. If 0 then plug is bad. If other then disconnect all plugs and check for 12 volts from wire to ground. If no or low voltage then suspect short in wire.

If the glow plug is shorted out the meter will indicate infinite resistance(open circuit) not zero.

 

[dbotos]

Current draw will be much easier to measure accurately than resistance unless you've got a nice Keithley 4-wire ohmmeter just laying around. Basically, you set up a manual circuit with a push button switch and measure current draw for each glow plug. Here are my adventures doing so:

http://www.tractorbynet.com/forums/kioti-owning-operating/352708-resistance-spec-lb1914-glow-plugs.html

Your smoke behind the dash sounds like a glow plug timer module or relay got roasted. You can run the glow plugs off a manual circuit if needed - just make sure the wire and switch are beefy enough to handle the total current draw for the time duration. Mine is currently 10 AWG with a 20 A switch. I've got a 60 A switch and a 60 A maxi fuse + holder that I need to install.

 

[k0ua]

Guys, I know a lot of you are just trying to help, but there has been some erroneous info given.

Lets try to clear a couple of concepts up. An average glow plug has a resistance of about 1/2 of an Ohm. That is Soooo close to a "dead short" a lot of meters and a lot of people would not be able to discern the difference. An open is infinite resistance. Zero ohms is a very very low resistance. When we get around 1 ohm of resistance it is very difficult to to interpret lower resistances without a special expanded scale meter. You would be hard pressed to find a zero ohm resistor. A chunk of copper wire is getting there, but copper wire has some resistance too, but you sure as heck cannot measure it on an average ohmmeter.

When a load is placed across a power source like in this case putting glow plugs across a battery, the lower the resistance of the glow plugs the more current will flow. And 3 or 4 glow plugs EACH with a resistance around 1/2 an ohm or so will draw a chitload of current the instand they are connected. Now when they start to heat up, and that occurs real quick, the resistance of the glow plugs go up and less current is drawn a few seconds after they are energized than the immediate starting current.

Keep in mind that 3 or 4 glow plugs in parallel, and that is how they are hooked up, will draw more current than a single plug, because resistors in parallel have less resistance than any single plug.

Examples: and open circuit or infinite resistance does not draw any current for a given voltage. A 1000 ohm resistor will draw less current than a 100 ohm resistor. A 10 ohm resistor will draw less current than a 1 ohm resistor. and on down to a zero ohm resistor will theoretically draw an infinite amount of current. That's a whole big bunch for those of us that are numerically challenged. of course finding a zero ohm resistor is kinda hard to do, and there is a limit to the amount of current that a battery will deliver, but here is fun experiment. Just drop a nice big wrench across your battery terminals and run like he77. A lot of current will flow, a whole lot of heat and light will be emitted, and hopefully you will be somewhere else when that happens.

So again, just trying to help clear up some misconceptions about the terms and Ohms law. Remember Ohms law is not just a good idea, it is the law.

 

[MT2501owner]

Thanks guys. I'll check them out individually.
If I understand correctly, a glow plug that is shorted out is open, like a bad light bulb. If the wiring is shorted out, it could be closed like a bare wire touching a ground, or open like a broken wire.
??

 

[dbotos]

open = resistance near infinity, current pretty much zero (like a light bulb filament burnt out) (think of it like a draw bridge being open - electrons can't travel across)

shorted = resistance near zero, current as high as source can provide (good for melting stuff as in k0ua's wrench-across-the-battery-terminals example)

 

[brain55]

Thanks guys. I'll check them out individually.
If I understand correctly, a glow plug that is shorted out is open, like a bad light bulb. If the wiring is shorted out, it could be closed like a bare wire touching a ground, or open like a broken wire.
??

Glow plugs can be shorted to open or shorted to ground. Had a machine yesterday that was melting the 100 amp fuse out of it as soon as you turned on the key. The starter and alternator were unfused straight from the battery, the fused power powered everything else. All the circuits were individually fused except for the glow plugs. I put a 200 amp shunt inline just to see where we were, I had never seen it go over limit until yesterday. As soon as my tech turned the key on the ammeter went over limit (the glow plug circuit is automatic). We replaced the glow plugs, no more problem.

Brian

 

[dbotos]

Short to open is an oxymoron.

https://en.m.wikipedia.org/wiki/Short_circuit

 

[brain55]

Short to open is an oxymoron.

https://en.m.wikipedia.org/wiki/Short_circuit

Yeah I know :-(

 

[dbotos]

In the short circuit, the wire would probably melt / smoke and the battery could get hot from rapid discharge and possibly explode.

 

[Coyote machine]

Thanks guys. I'll check them out individually.
If I understand correctly, a glow plug that is shorted out is open, like a bad light bulb. If the wiring is shorted out, it could be closed like a bare wire touching a ground, or open like a broken wire.
??

I think you're overthinking the problem. The glow plugs are either not working ~ open, (broken), or they are working properly, as in NOT open/broken, etc.
When the glow plugs are working properly the resistance they produce to the current flowing to/through them generates HEAT, and this results in the precombustion chamber of your tractor's individual cylinders getting hot and assisting in starting in colder weather.
When the glow plugs are not functioning, less heat is generated, and it is harder to start the tractor. Diesels are compression ignition (CI), unlike a gas engine where spark, (SI) gets the fuel to ignite.

If you have smoking wires, or other items causing smoking under your dash, that issue needs to be fixed too. As suggested you may have been burning a glow plug relay's contacts or some other circuit protection device. Either way, it needs to be investigated and solved.

 

[Jerry/MT]

If the glow plug is shorted out the meter will indicate infinite resistance(open circuit) not zero.

Poor choice of words on my part. As pointed out, an open circuit is not a short. Sorry for the confusion