glow plug diagnostics
 

Got a multimeter, went to test my glowplugs a la Diesel Giant's tutorial, and can't stretch the negative probe to the battery and simultaneously test the glow plug ports (they are on opposite sides under the hood). What do you guys do, use an extension wire wrapped from the negative post to the multimeter?

Little obstacles....


I'm pretty sure my glows are in a bad way; it was 40 degrees today and I had to crank three times, 10 to 15 seconds each, before it would turn over.

You can use a wire with alligator clips to extend the negative lead to reach the battery. Or, you can just find a clean place on the engine block to touch the negative lead.

Well, I had two multimeters so I took the cord off one and hooked it up to the existing one as an 'extension'. Worked well.

I would think you could also just put the negative pole on something that is grounded, such as bolts on the engine block. I believe the reason they have you put it on the negative terminal is so that you are 100% sure you have a good ground.

You don't HAVE TO ground out the multimeter on the battery, you can use any good ground. The readings you get may not be as precise, however as in my recent case, it doesn't really matter how precise you're resistance readings are when 3 GPs are completely open (infinite resistance). If you have some GPs on the brink of acceptable resistance you may want to ground directly to battery to get a more reliable reading.

I can't get a reading so far....I've tried putting the negative cable on about a dozen different places all over the engine, while keeping the positive lead inside the glow plug connector #1. Any ideas?

got kind of a sketchy reading on port #1--meter jumped around, kind of oscillated between 1.4 and 1.8. Nothing on the rest. Guess I'll try to jerry-rig some sort of wiring to the battery, just to get a good ground.

This seems like it's just as much work as replacing the glows--though I've never done that and the #5 plug looks like a tough one. What tools do you need to disconnect the wire and unscrew the glow plug itself? Haynes says "a suitable wrench". Any way to get more specific on that?

Sounds like you are doing something wrong. Ground your negative lead although it does not mater if it is the negative or positive lead. Touch the other lead to some other grounded point. Or touch the two meter leads together and mention on site what is indicated. Might be a start for others to help. It is still the easiest way to identify burnt out plugs usually.

Just bought some 12 gauge wire to extend my negative lead to the battery. Will go test with that solid ground tomorrow.

When I touch the leads together the meter jumps around, finally oscillating between .1 and .3. It never settles on a value.

This isn't rocket science, so I'm wondering what is going on....

Is your multimeter working correctly? Is the multimeter battery new? Test for volts at the battery to make sure your leads are good.

John

Sounds like the meter is not perfect. Or it's battery is low. Still good enough for your test though. It could be intermitent leads or oxidized plugs but think not as the given values are pretty close.
Anyways consider the oscillation as a meter problem for practical purposes. You are looking for low values on each plug. Usually a burnt out plug will be wide open. You still might notice a plug with increased resistance . The oscillation range should vary if there but at slightly higher values when it settles down.
As you say not rocket science but confusing to some exrent depending on amount of experience using a meter. Usually the worst problem reading things is getting good clean connections with no oxidation on your points of contact.

If you touch the probes together you should get a steady zero, or close to it. Do you by chance have it set on voltage? That'll give you funny readings if there's no voltage. Also if you meter doesn't auto-range, make sure you have it on the right range...you're only measuring 1 Ohm. Just for fun, get a light bulb and put one lead on the metal tip and the other lead on the threads, that'll give you some resistance.

If you can get your hands down by a plug, but one probe on the back end where the wire connects, and the other probe on the engine block (anything big and metal on the car can be a ground) or on the body of the plug. That will directly measure the resistance across the plug.

Then check the wires, one probe on each end of the glow plug wire.

Good luck

............the digital multi-meter strikes another innocent victim.........yet again.

If I ever decide to buy one of them..........please shoot me.

Carlton, you use an analog one? I just bought this POS on Saturday from Radio Shack so I'll just go return it, no big deal. When I put the leads together they jump between .1 and .3 for about 10 seconds, then zero out. Should it just always be at zero, no questions asked?

It measured the battery fine at 12.73 volts, so I'm thinking the meter should be ok....but when I'm on Ohms at the "200" dial mark--which is where the Haynes manual says to go, and where it is on Diesel Giant's tutorial on glow plugs--I can't seem to get the ground situation sorted out. I touched the negative lead all over the engine metal, various bolts, etc., and got no reading on the glow plug ports.

Anyway, I'll give it a shot with the jerry rigged piece of wire connecting to the negative battery terminal tomorrow.

The car cranks like a bastard and barely turns over after sitting for a cold night. Something's up.

Again, what tools do you guys use to remove the actual glow plugs?

How often do you have to replace glow plugs living in a relatively cold climate?

Thanks

I have a $10 Radio Shack analog meter (cigrarette pack size) that does 99% of my troubleshooting. It cannot measure 1 ohm, so I use the $50 analog meter for that. The $50. meter gets used once every two years.........if that.

I don't comment on the function of digital meters. Too many folks have gotten way too confused by their displays and their questionable accuracy and repeatability. This might be due to the fact that they are low cost meters.........

An actual wrench is needed for actual glow plugs. You can remove imaginary glow plugs with anything you like. When I am in hurry, I just call Snow White and have her send over five of her best dwarfs.