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.

Can I get her number? I could have used a couple dwarfs on Sunday. I asked my 5 year old to trade hands, but he said NO.

You either have a really wide 123 or really short wires on your multimeter. I put the multimeter in the middle of the engine. I stick the black wire in the ground connection. I stick the red wire in the plug.
Mine reads .4 when I hold the wires together. When I test the plugs I get 1.0, so I subtract .4 from 1.0 and get .6, which is good. I have an analog one too, but I like the digital one better. Some day I'll get a really nice one that can zero out.

My $15 POS digital meter seems to work OK, it reads 0 ohms when I touch the leads together and someplace in the 0.5 to 1.0 ohm range on a good GP, close enough.

I just use short open end wrenches on the GPs, if you want to get fancy, buy a ratchet wrench.

tangofox, can I just call you and have you come over? That'd be as good as 5 dwarfs, easy. :)

My $3 Harbor Freight multi-meter does just fine. I typically test the plugs right at the plug itself to rule out any harness problems.
I don't see the point of grounding at the battery. You're testing the resistance of the plug so I would think it's better to ground to the engine block since that is what the plug is grounded to. Why introduce the variable of the engine ground strap into the equation?

I use fantastic gear wrenches to remove my dream glow plugs and actual gear wrenches to remove actual glow plugs. If things get really tough I reach in my toolbox for the Platonic Form of Gear Wrenchness.

Isn't it hard to rule out a harness problem if you omit the harness from the test?

I'm testing the plugs so I'm ruling out the harness as a possible cause of deviant readings.

I just test through the harness, then check the plug to make sure it's not the harness if/when I get a bad reading.

I just ground to the head when i ohm plugs. I use a $20 Radio Shack meter which works well enough for that.

For removing wires and plugs I use 8 mm and 12 mm combination wrenches respectively. Some folks find it easier to remove the injector lines before attempting to change plugs. I don't, but I have pretty small hands.

a ratcheting wrench is wonderful for removing and replacing GPs.

I use the bolt that holds the relay on the fender. I also use gear wrenches.

I used the 8mm open end wrench for the nut on the GPs, then either a 12mm wrench or socket on the GPs depending on what was easier to reach them with. I just changed all 5 in my 300SD yesterday, took about 2 hours. (Tom if you can change them all in 20 minutes you need to be on a pit crew!) Wish I had some ratcheting wrenches. I'll pick some up at Harbor Freight next time, $8.99 for a set! The GP next the firewall is difficult to reach. Hope you have small hands!

John :D

Results
 

Grounded at the battery thanks to some alligator clips and 12 gauge wire. Meter finally produced results. I tested at the glow plug connector. Here are the results.

GP 1 = 1.5 ohm
GP 2 = 1.3 ohm
GP 3 = OL
GP 4 = 1.4 ohm
GP 5 = OL


Then I reached in and tested at the plugs themselves--or as close to touching the wand to the plug as I could get. With this test, both plugs 1 and 2 were the same, but plug 3 gave me 1.3 ohms, while plugs 4 and 5 didn't register anything.

Does this point to the harness (wire that goes between plug and relay, right?) for plug 3?

Well, I'm done for now.....dropped my 8mm wrench down beyond the 3rd glow plug! It's a tiny wrench and I can't reach it. Guess it'll either stay there for a while or fall out. Tried getting it with a magnet but I don't have anything that'll reach down that far. At least I can tell my mechanic that it's probably the 4th and 5th (and maybe 3rd) glow plug. Hope the wrench doesn't get loose while I'm driving it and destroy anything!!

Rule number one for glow plug work: Jam rags down between the block and IP and oil filter housings so wrenches and nuts can't disappear.

Does seem like there's a harness problem. That's not very common. I'd check the resistance on each wire between the relay and the glowplug end.

Something is still strange. You are still getting non consistant results in my opinion. If the meter is a recent aquisition take it back if you can. Barring that borrow one.
I very much doubt the wiring harness has some open leads. Anything is possible yet..... You will find a normal working meter to be much nicer to use. At this point I would not trust that meter you have. Most meter problems are constants but your meter may be throwing a few curves in for good measure. Since you have alligator clips etc try putting a 12 volt light bulb between the positive terminal of the battery and each contact in the plug. If it lights the plug for most practical purposes is probably useable. If it does not light you have an open plug most likely. I suspect your results might be different than your meters. Sorry to see you having so much trouble.

At autozone they have magnets on an extendable stick. I dropped a wrench and a screwdriver bit down there and got them both out with the magnet. You can get your wrench out..its big enough for the magnet to find easily..keep trying!

As for wrenches, I used gear wrenches for both the little nut and the plug, but next time I'm going to go to sears and buy a craftsman 12mm ratcheting box end wrench with a nice 5 degree swing, because my gear wrenches almost didn't cut it...I have barely enough room to swing the wrench. But its not that hard...I was a little daunted by a few of them and they turned out to be easier than I though. And since its something that you've going to have to tend to every year or two, it would probably be best to get familiar with changing the plugs.

Good luck, and don't forget to put anti-sieze on the new plug threads to make your work easier next time around.

Sears makes a pick up tool (drain snake looking thing with opening claws) that can pick the wrench up out of the crack. Ask me how I know...

http://www.sears.com/shc/s/p_10153_12605_00941322000P?keyword=pick+up

I can do mine in 20-30 minutes without a problem, they unscrew with just my fingers once I loosen them about 1/2 turn. It gets easier after you've done a few.

I ended up getting my 1/2" ratchet driver down in the crack, batted the wrench out of sight, and reached up from underneath to grab it. I will stuff rags down there--thanks Kerry. Nice to know rule #1 about a job after having broken it :):):)

I will be MUCH more inclined to chase down these discrepancies/unscrew the wires/plugs once it's not freezing outside. I am moving to Austin, TX later this year, so in the mean time, i think this will go onto the list of things the mechanic will look at in the upcoming week. I don't know if you guys remember but I posted a month or so ago about a whole mess of front end rebuild work, with parts prices and labor quotes. The unanimous decision was that the mechanic was very reasonably priced. So, the wagon goes off to get $1600 worth of bushings and whatnot installed.....here's the link to that thread, in case you're curious:

http://www.peachparts.com/shopforum/diesel-discussion/210145-recent-brake-job-you-were-right.html

Luckily I just got married this past fall, so we're putting all our wedding gift money toward this laundry list of fixes for our car. The wife is behind it. Without this money we couldn't afford to do this, no matter how reasonably priced it is. $1600 is a lot to put into a car that ostensibly runs well enough. Alas.

Thanks again for all your guys' help! This forum makes jobs easier; lacking a proper set of tools and buying faulty meters makes it frustrating...and all you can do is smile :)

(and go broke)