Glow Plugs

[Trains1938]

Hi, How do you test the glow plugs in a 254 Jinma tractor? Mine is hard starting and I don't know if the glow plugs are working. When I put the start switch in the heat position the amp meter does not move. Checked the fuse and it seems to be ok.

 

[CobyRupert]

If you want to leave them in place, you could test them with a continuity tester, or more accurately with an ohm meter.
If you figure your battery voltage (“V”) is 12.6 volts, and you measure the resistance (“R”) in ohms, the heat the plug generates is V^2/R, or 12.6^2/R, or 158.8/R (Watts).
So if you measure R as .5 Ohms, it should produce 318 watts of heat.

 

[piper184]

If your amp meter works properly otherwise that is a pretty good indication that your glow plugs are not working. The big question is why?
I would start by putting a volt meter on the bus bar that connects the glow plugs and check for battery voltage when you hit the Heat switch.
If you see battery voltage at the bar, all the circuits are good and most likely all the glow plugs are burned out. If you don't get battery voltage you have to work your way back along the circuit to find the problem.

You can check the resistance of each glow plug but you have to remove the buss bar and do it on each plug individually. I thought I had a listing of what resistance to expect but can't find it. In any case, if you have an open circuit between the tip of the plug and ground, the plug is bad.

 

[Trains1938]

If your amp meter works properly otherwise that is a pretty good indication that your glow plugs are not working. The big question is why?
I would start by putting a volt meter on the bus bar that connects the glow plugs and check for battery voltage when you hit the Heat switch.
If you see battery voltage at the bar, all the circuits are good and most likely all the glow plugs are burned out. If you don't get battery voltage you have to work your way back along the circuit to find the problem.

You can check the resistance of each glow plug but you have to remove the buss bar and do it on each plug individually. I thought I had a listing of what resistance to expect but can't find it. In any case, if you have an open circuit between the tip of the plug and ground, the plug is bad.

 

[Trains1938]

Hi, piper checked the voltage at the bus bar. I am getting 12.4 volts. So what do think? Are they hard to pull out? It is hard to think that all 3 of them go bad at the same time.

 

[Trains1938]

I'd think you could test them with a volt meter, too, or a light. Just connect volt meter or light to top of glow plug and other side to ground. Turn to glow position with ignition switch and see if you get voltage or light on.

 

[Trains1938]

Hi Ralph, this method only confirms power to them, not if they are working. I tested the voltage to them and I am getting 12.4 volts.

 

[CobyRupert]

 

[RalphVa]

Hi Ralph, this method only confirms power to them, not if they are working. I tested the voltage to them and I am getting 12.4 volts.

I realized my mistake and deleted it.

 

[bearthebruce]

So you have voltage to all three? You are assuming the voltage on the bus bar is connecting to the glow plugs? Shouldn't you verify that?

Did you measure each glow plugs resistance? Do you see a resistance on your meter.. probably takes a pretty good meter as these will be relatively low value resistance - as in an ohm or less.

If the resistance is where it ought to be, and the voltage is reaching the plug, then the only other possibility is the ground circuit. One would assume the block of the engine has been connected to the negative terminal of the battery. But, I have been in China and seen some of their wiring!!!! Assume nothing.

 

[Roadworthy]

You can check the specific model of glow plug you use but in manu cases the nominal voltage is about 10.5. If you're measuring 12.6 they are probably not pulling any current (open) to drop the voltage. They may not have all gone bad at once, they could have failed one at a time and you never noticed it until you had total failure.

 

[Trains1938]

So you have voltage to all three? You are assuming the voltage on the bus bar is connecting to the glow plugs? Shouldn't you verify that?

Did you measure each glow plugs resistance? Do you see a resistance on your meter.. probably takes a pretty good meter as these will be relatively low value resistance - as in an ohm or less.

If the resistance is where it ought to be, and the voltage is reaching the plug, then the only other possibility is the ground circuit. One would assume the block of the engine has been connected to the negative terminal of the battery. But, I have been in China and seen some of their wiring!!!! Assume nothing.

Hi bearthebruce, I just checked voltage at one end of the bus bar. No I have not measured the resistance on any of the plugs. Not sure how to do that with the plugs still in the engine. Note: They use to work, at least the amp meter use to show a heavy draw when I went to heat position on the starter switch and now shows nothing.

 

[bearthebruce]

To troubleshoot, you are going to have to take them out like Roadworthy suggested... I find it hard to believe they all have gone bad... but, they may have. No current would indicate they open.. not heating at all.

 

[Trains1938]

You can check the specific model of glow plug you use but in manu cases the nominal voltage is about 10.5. If you're measuring 12.6 they are probably not pulling any current (open) to drop the voltage. They may not have all gone bad at once, they could have failed one at a time and you never noticed it until you had total failure.

That is a possibility, because it has been hard to start since I bought it. Do you know what size socket it takes?

 

[RalphVa]

Could disconnect the wire to each one and put a light in between the wire and the top of the glow plug and turn switch to "glow" position to see if light turns on. Do on each plug.

We had a 240D Benz we kept until 26 years old. Didn't get glow plugs to burn out until well over 150k miles. Only then, it took 2 out of the 4 to be noticeable.

 

[Trains1938]

You don't have to take them out to test them. Disconnect the buss bar from all of them (or the wire), and measure the resistance of each plug from the connection point to the engine block. You should get a reading of less than 1/2 ohm to be good. Chances are you will find that they are open. Then you'll need the socket.

Hi K7LN, I will try it. It has turned cold here so I will wait until it warms, a day or to. Let you know how it turns out.

 

[Trains1938]

Hi K7LN, I will try it. It has turned cold here so I will wait until it warms, a day or to. Let you know how it turns out.

Hi K7LN, It has warmed up so I just tried what you and others suggested. Checked the glow plugs in the block. All 3 of them showed .5 oms, not sure if that says they are ok or need to replaced. What do think?

 

[bearthebruce]

That seems to be a reasonable number.. under load, you would be pulling about 20 amps through the plug.

So why aren't ya is the question!

If the power bus is getting voltage when the glow plug is switched on, and the resistance is there, then the only thing left is the ground. The block is connected to the (-) terminal of the battery? That cable is in good shape?

 

[CobyRupert]

If it’s a bad negative battery terminal cable or its connection to the frame, why would starter still work?
...but OP says it has always been hard to start. Even in warm weather too?
Could be the negative connection, but strange enough current makes it through for starter but not plugs.

 

[Fuddy1952]

Years ago I had a VW diesel pickup. I have an inexpensive inductive analog ammeter I used on each glow plug wire to check them.
Or I'd just cycle them on a few times, then feel each one see if they were all warm.