It looks like when one of my diesels goes bad the other one follows. I replaced my Glowplugs about 16 months and 15,000 miles ago., Having trouble starting when its only around 40degrees out.

I checked the volatge for the GP relay and all posts get 12 volts. It seems to me that only two of the plugs are now any good, cant get any reading from four of them.

Could someone confirm that I am checking them correctly? I took off the connection from the GP relay and stuck the Multimeter prong in each of the sic connections. ONly the cyl 1 and 3 read 1.6 The others dont read anything.

Plus can someone tell me how the cylinders are numbered?

Lastly is there a test for the K40 relay? Thanks guys!

What car are you working on?

I've never had luck testing the ohms of the GPs. I always pull them out and give them 12v, and see if they get bright orange or not. Careful, they get REALLY hot, something like 1600*F. If they don't turn bright orange they they are sub par and should be replaced.

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Those readings probably mean bad plugs. Leave the harness unplugged at the relay and test again at the plugs. That will confirm which ones are bad.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Good start, I think. Depends on which 'posts' you are measuring. 12V at each glow plug (measured from ground to GP connector) is good and means the relay is sending power to each plug.

I assume that you put the multimeter on OHMS setting, connected one lead to GROUND and are touching the connections one at a time. A 'normal' reading should be 1-3 ohms, or so. A flashing reading usually means that the connection is open.

Should be #1 in front, then #2, etc. towards the firewall.

The problem with replacing GPs one at a time is that the resistance can vary on old used ones even of they still "work". This will kink the entire system, if I understand correctly. They are so cheap that I just replace them as a set, like spark plugs on a gas car.

Well GP's arent cheap like spark plugs, about $25 each. I just replaced them last year. Only want to replace the ones that arent working because this I believe 606 engine is a bear to get them out.

One came out okay but when I tried to get the second one out it wouldnt budge and like I said it was about a year ago and I reamed the hole and put anti-seize on the treads. Man I dont want to deal with a broke one at this time.

When I measured the volts I un plugged the relay and put the multimeter wand on one of the six posts at a time, all were 12 volts.

If the multimeter stays at minus one it means its bad I presume which occurred to 4 out of 6 and the other two measured 1.6 ohms.

Sorry I forgot what test to see if K40 is OK? I took it out on this 97 e300d and all the soldering looked good without any corrosion.

Assuming that the multimeter reads (-1) when the leads are not connected, or open (not all multimeters display an open the same way) you would be correct that 4 of the 6 are open, or burned out.

I'm confused. How were you getting voltage if the relay was unplugged?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Its measured at the male part of the glow plug relay.

That method doesn't check the harness wiring.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

[QUOTE=jmbeam;2806709]Well GP's arent cheap like spark plugs, about $25 each. I just replaced them last year. Only want to replace the ones that arent working because this I believe 606 engine is a bear to get them out.

What year is your 606?

My glow plug circuit seems to have some kind of monitoring system in it because if I loose just one (of any six) glow plugs, the GP light will not illuminate until after the car has started, and will stay illuminated until I replace the fault glow plug(s). The glow plug cycle still powers up the working gp's even though I don't get the pre-glow light.

My car is a 93 E300D.

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1995 E300 Diesel

My 606 is a 1997. Looks like 1 and 3 GP are good. There is no way Im going to get the rest out unless I take off the Intake manifold again. This is BS these NGK GP's should last longer than a year and about 18K mileage. To be honest Im not sure why after having these all done a tear ago that these plugs are snug in again. It took 4 days to get them out before because I was so worried I would break one in the head.

BTW Kerry I was just checking voltage at the GP relay. I checked the OHms of the GP through the harness

BTW Biodiesel300TD I read that one can burn out a GP if hooked up tpo a 12 volt source so I didnt try that method.

ANY have a test for the K40 relay????

1) Disconnect gp connector at driver's side fenderwall.
2) Measure resistance between each contact and ground. Connector is numbered 1-6. Cylinder one is nearest to radiator.
3) Resistance of a good gp should be 1-2 ohms. If it reads open circuit, gp is probably bad.
4) "probably" means remove the IM, confirm open circuit between each GP post and ground.

I've had some gp last years, and some burn out within a year.

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Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k