Bad Glow Plugs?

[GregFrench]

1981 2H

My glow plugs aren't working. How do I know if it is bad plugs, or something else before I order a set? My light stopped working a month or so ago, but it seemed the plugs were still working. Now the plugs don't work. I hear the realy working when I turn the key backwards, so I know power is making it that far.

I did a search and read that there is a way to test the power going to the plugs. Could someone explain this procedure to me (with pics). Explain it as though I don't know anything.

Thanks!

 

[jmylie]

I would doubt that all of your glow plugs would go at once.

I would suspect an electrical issue.

 

[GregFrench]

I don't know if they have ever been changed, so they all probably need it.

Once I get them out, how do I check to see if they are working. I read about connecting a wire to my + lead and grounding them out on the engine or something.

Anybody know what fuse it would be before I try the hard more mechanical stuff? I have no owners manual, and they are not listed in my service manual. There is nothing anywhere telling me what the fuses go to.
The relay is clicking, though, so at least something is getting power.

 

[lostmarbles]

1981 2H
My glow plugs aren't working. ... My light stopped working a month or so ago..........., I hear the realy working.......... a way to test the power going to the plugs. Could someone explain this procedure to me (with pics). Explain it as though I don't know anything.

OK Greg. I'll have a go:------

Your battery provides the pressure (called "voltage") that forces current to flow through your lights, horn, wiper motor, glow plugs, etc.-- when you switch them on. It is this current flow that makes them work. Electrical people give these motors, lights and heaters a general name called "loads".

By "switch on" - I mean------ "when you close that final "switch" that provides a "continuous electrical circuit" from the positive side of the battery, through the "load" and back to its negative side.

In our vehicles "fuses" and "fusible links" protect these loads and their associated wiring from the damage that would otherwise result from short-circuits. (A "short-circuit" is where the current has found an abnormal "quick route" back to the battery. For instance via an exhaust pipe when part of the wiring has fallen onto it and the protective insulation has melted.) A fuse or fusible link protects loads and circuits by "destroying itself" (by melting as a result of EXCESSIVE current flow) and thereby provides a break in the circuit that prevents further current flow.

So one of the best ways of searching for electrical faults is to test to see where this voltage/pressure is present and where it is missing. The most common way of testing this is with a voltmeter. Here is a photo of a cheap digital meter being used to check whether the glow plugs on my BJ40 are getting voltage. (The meter shows 0 Volts now because no-one is in the cab turning the glow plugs on. If my son wasn't such a lazy sod -still asleep!!!- I'd get him to turn them on to also show you the higher reading I would get then.)

Note that there is a "buzz bar" connecting all the glow plugs together on my BJ40. This "bar" is supplied with voltage from my glow plug relay (through its "high current" open/close contacts). That current must travel back to the battery and it does so via the engine block, chassis, and the earthing lead(s) that eventually connect to the battery's negative terminal.
It can be hard to use a meter like this without assistance unless you have a "crocodile clip" attached to your earth lead that enables you to earth the voltmeter's negative probe like this:

I should explain what I mean by "earth". The battery's negative terminal is connected to the metal bodywork/frame/block etc via the "earthing" leads. So we call any of these places "an earthing point". The crocodile clip is attached to an injector pipe in the photo. That pipe is "an earth" because it is directly connected to the battery's negative terminal through flanges, bolts, and earthing leads.




t to switch (connect/disconnect) a high current. (If you use a normal switch to switch a high current, arcing/sparking will damage that switch.) You say you still hear your relay "clicking" so therefore it is still

 

[lostmarbles]

Anybody know what fuse it would be

I'm not familiar with your vehicle - But I would suggest checking your fusible links first.

 

[GregFrench]

Sweet. Thanks for the "Intro 101" lesson.

So to test if my buzzbar is getting power, I can put the + lead of the mulitmeter anywhere on it and touch the - to any ground while someone turns the glowplug switch on. If it is getting power, then the plugs are getting power but aren't working and, therefore, probably bad.

If this buzzbar is not getting power, there is probably a short somewhere, which might explain why my battery went dead just before my glowplugs stopped working.

Is this what I should have gotten out of this?

 

[UpsideDown]

Taking a reading from the BUSS bar is just checking to see if power is getting to the plugs.

To test the plugs, it's really best to remove them and glow test them while out of the vehicle so you can see how long they take to glow, as well as how well they glow - if they aren't lighting up the lower 1/3 to 1/2 of the plug, including the tip, they should be replaced.

It is a good idea to replace all the plugs at one time.

Cascade failure can happen when one or two plugs go and the rest get too much current (the circuit relies on a certain amount of voltage drop) and glow too brightly and burn out. Usually you will find one or two that are burned out, or one or two that are glowing weakly (or taking too long to glow, compared to the others).

Check that the glow indicator light on your dash still has a good bulb in it.

hth, ymmv.
~john

 

[lostmarbles]

Sweet. Thanks for the "Intro 101" lesson.

So to test if my buzzbar is getting power, I can put the + lead of the mulitmeter anywhere on it and touch the - to any ground while someone turns the glowplug switch on. If it is getting power, then the plugs are getting power but aren't working and, therefore, probably bad.

If this buzzbar is not getting power, there is probably a short somewhere, which might explain why my battery went dead just before my glowplugs stopped working.

Is this what I should have gotten out of this?

Yep.

 

[Diesel Weasel]

Cascade failure can happen when one or two plugs go and the rest get too much current (the circuit relies on a certain amount of voltage drop) and glow too brightly and burn out. Usually you will find one or two that are burned out, or one or two that are glowing weakly (or taking too long to glow, compared to the others).

Exactly. Each and every time I have had glow plug failures I have found that all of the plugs needed to be replaced.

 

[crushers]

you do not have to remove the glow plugs from the the engine, just remove the buss bar and test each plug.
i have seldom found all plugs gone at once.

 

[brownbear]

If this buzzbar is not getting power, there is probably a short somewhere, which might explain why my battery went dead just before my glowplugs stopped working.

Is this what I should have gotten out of this?

if the busbar isn't gettting power then go to the relay(round one on the fender LH side). check there for power on both sides of the connector. You most likely will have to pull the connector apart and just see if power is at the relay.

The fusible link at the battery provides the power to the relay.

A short means a short to ground(as in short cut). If you have a wire go bare to ground it draws much more current and blows the fuse(fusible link).

I think your fusible link may be blown from being old and heated lots, or you have a few plugs bad.

If you download the FSM from the online manuals it will describe in easy to understand methods for testing the system. You want the 2H/12HT manual....

 

[ECMO4]

What kind of voltage should be going across the buss bar? Working similar issue on my 2H and getting 4.8V on the bar. Seems like it should be higher.