glow plug diagnostics - Page 2 - PeachParts Mercedes-Benz Forum

Bio300TDTdriver · #16 02-25-2008, 10:01 PM

Quote:

Originally Posted by tangofox007

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.

Bio300TDTdriver · #17 02-25-2008, 10:08 PM

Quote:

Originally Posted by JBG

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 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.

#18 02-25-2008, 10:14 PM

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.

JBG · #19 02-25-2008, 10:27 PM

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

kerry · #20 02-25-2008, 10:50 PM

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.

tangofox007 · #21 02-25-2008, 11:01 PM

Quote:

Originally Posted by kerry

I typically test the plugs right at the plug itself to rule out any harness problems.

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

kerry · #22 02-25-2008, 11:12 PM

Quote:

Originally Posted by tangofox007

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.

#23 02-25-2008, 11:34 PM

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.

Skippy · #24 02-26-2008, 12:56 AM

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.

thesst · #25 02-26-2008, 03:26 AM

a ratcheting wrench is wonderful for removing and replacing GPs.

toomany MBZ · #26 02-26-2008, 05:38 AM

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

hangit · #27 02-26-2008, 09:02 AM

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

JBG · #28 02-26-2008, 11:55 AM

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?

JBG · #29 02-26-2008, 12:18 PM

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!!

kerry · #30 02-26-2008, 01:16 PM

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.