How does a glow plug work?

[rasorbackq]

So at the beginning of the season noticed tractor (brandson 4720H) was getting harder to start on cool mornings. To a point when it just didn't. Just rolled over and over. We had a break in the temp a little so I picked up 4 glow plugs Thinking I could replace them all or what ever was required. . Since I had to remove the metal strip running to each plug and just replaced the first 3 . Last one is very difficult to get to.. 30 minutes later I'm all done . Fires right up in 5 seconds. Next day 5 seconds . Next day 5 seconds. Today no go. Glow plug light on dash is not even lit. Checked all fuses all good. So what is the power that a glow plug operates on . 12V?? Is there any other devices or moduals if the lineto operate a glow plug?
All I can say is the glow plug wire is about 3 " long before it enters the harness. This is as far as I got so far. Storm coming in 4 days. Needs to be running.

 

[Roadworthy]

A glow plug works pretty much like any heater - apply voltage and it gets hot. Glow plugs normally get 10.5 volts though there are exceptions. Put a meter on your glow plug to check what voltage you're getting. Some glow plug circuits depend on a series resistor to drop the voltage. Some have an electronic controller and relay. You probably need the schematic for your specific tractor to see what's going on. If you want to measure current to see if the plugs are working figure on ten amps per plug.

 

[rasorbackq]

Only a 5 amp fuse

 

[WranglerX]

Only a 5 amp fuse

Hard to believe..... 5 amp for 4 plugs?.... ITs probably the control circuit to operate a relay someplace else.... I would expect at least 10 amp per plug, 4 in parallel would be 40 amp...

 

[Roadworthy]

As DL implied you definitely have some sort of controller or relay in the glow plug circuit. It may run on the five amp fuse but the glow plugs, when intact and energized, will draw about forty amps. You really need a circuit diagram to determine exactly how the glow plugs work. The controller will probably have internal regulation to limit your glow plugs to about 10.5 volts. It will NOT be direct wired from a switch.

 

[rasorbackq]

So without a drawing should I be looking inside console under the dash or under the hood . Maybe cut open the harness and start following?

 

[rasorbackq]

So without a drawing should I be looking inside console under the dash or under the hood . Maybe cut open the harness and start following?

 

[WranglerX]

I would try to find a manual first, then look under hood or "dash" for what may be a grouping of relays..... Cutting open a harness should be a last resort or just plain desperation... Did you check manual for tractor , mine has rudimentary wiring diagram included.... .

 

[LouNY]

The 5 amp fuse is going to be going from the switch to a relay or glow plug controller.
Starting under the hood try to trace back the heavy wiring from the glow plugs to were it goes.
In the Branson section of this forum all the service manuals have been linked for down loading
they will help you find what you need
.How does a glow plug work?

 

[rasorbackq]

So without a drawing should I be looking inside console under the dash or under the hood . Maybe cut open the harness and start following?

 

[rasorbackq]

Thanks LouNY I didn't know they were there......I know this is asking a lot . Can someone post for me the diagram from the branson area. I was just there and it 363 mg . My internet is sooo slow it will take til next month to load it. 4720H 2010 model
Thanks.

 

[jigs_n_fixtures]

If you’re not color blind you can chase wires by color. As was said earlier, start at the glow plugs and work back. I would expect that wire to go to a large relay. Once you are there you can check with a voltmeter, to see if the large feed wire to the relay is hot, and if the control wire is hot, when you move the switch on and off. If you don’t have power on the big lead to the relay, chase it back, and you’ll find either a fusible link, fuse, or a circuit breaker.

Some of the glow plug relays have timers built in, and it can keep the relay from closing if it fails.

This is all pretty large macro level stuff, and you can normally chase it by eye and hand. Manuals help, but aren’t really a necessity.

 

[LouNY]

The attached PDF is the electrical section,
I did see that the glow plug controller is mounted to the side of the engine and there is a relay for glow plug power.
I had to split the section in 2 to upload it.

 

[WranglerX]

This diagram seem to be the details you need....

.

 

[greggyy]

So without a drawing should I be looking inside console under the dash or under the hood . Maybe cut open the harness and start following?

eeek....do not start cutting things or harness, that is not how you diagnose !

as an auto spark, I can tell you not much without knowing the setup, ask the dealers mechanic first maybe if you do not have the electrical skills to diagnose.

I have 2 older tractors and both are mechanical switches to feed glow plugs, one engine needs the plugs, the other does not unless getting very cold, the glow circuit is actually broken, so what I do, rather than repairing electrics, is park it where it gets sun in winter & when need be, wind it over a few times then wait a min or two for that friction to raise the temp, then it will fire.

If you are taking time to sort it and you have a shed, keep it in there and use something to warm the engine, it should fire with no glow unless it is one of those engines that really needs it.

 

[jigs_n_fixtures]

Don’t cut anything. From the battery is a heavy red wire, it splits to two wires fed through fuse able links one wire is white it goes to the keyed switch. The other is yellow and goes to the glow plug relay. Is there power after the fuseable link? If there is power after the fuseable link, does it get to the relay?

the relay has two yellow fires coming to it which are both yellow, one big wire from the fuseable link, and a smaller yellow wire from the glow plug control box. Leaving the relay are a small black wire, and a heavy white wire with a red tracer which goes to the glow plugs.

This is where things could get tricky. If the controller is good, and the engine is cold, the key will feed the controller and it will feed power to the small yellow wire and pull in the relay, feeding power to the white with red wire which feeds the glow plugs.

 

[K5lwq]

The controller also looks at the coolant temperature to determine how long the glow plugs are on. If you are using a coolant heater that may be your problem. Try unplugging the temp sensors and see if the glow plugs will get power.

 

[5030]

Sort of like your 'personal' glo plug. You get it hot, stick it in and it 'ignites' the mixture.

 

[rasorbackq]

ThaNKS

The attached PDF is the electrical section,
I did see that the glow plug controller is mounted to the side of the engine and there is a relay for glow plug power.
I had to split the section in 2 to upload it.

Thanks you very much Louny for the diagrams and Dl meiesin

 

[rasorbackq]

Talked to the tech at at dealer ship. He told me where the fusable link are . I tested them and both good. He suggested I apply 12 volts from battery right to glow plug strip . Be very careful he said.
In a crunch it will work. I haven't done that as need 2 people to do it One to operate the switch and the other operate the jumper.

After looking and reading the write up . First thing is key is on glow plug lite should be on .NOt on. Only appears to be 2 fuses for that . Both check out . Unless there is nothing coming from BR1 pin on switch.