Good morning folks. When I turned the key the glow plug dash light did not come on. Car started rough and then the dash light came on but eventually went off. I tested the glow plugs and the gp wires and these items are good. My glow plug relay is the newer type (without the metal strip fuse). I check all my other fuses in the fuse box and they are also good. So is there any thing else to check? Should I replace the glow plug relay? Thank you for your help!
JT

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JT
1991 350SD 216,000

Flip the key on and see if you get battery voltage to the glowplugs. I just tested my car yesterday, all good (first time something has been in perfect order when I checked it, yay). Not real sure about how your car differs. Good article at http://dieselgiant.com/glowplugrepair.htm

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1985 300D, 237k.
1994 F-350, 6.9 diesel, 5 spd manual, Banks Turbo. 261k.
Sold: 1985 300CD- 267K

Thank you TWeatherford. I went back through the testing process again with the Diesel Giant instructions. The car is a 1991 350SD.

All my glow plugs read .1 except for one that read .3. I had my meter set on RX1k. I had a new bosch gp and I tested it on same setting and it read .1, so I believe all GPs are good. I retested the wires, the same meter setting and they read same as GPs at .1. I have 12 volts at red wire feeding GP relay. I turned ignition to GP position and had 12 volts coming out of each male prong on GP relay.

Also, when I turned the ignition to the GP position and left it there after about 20-25 seconds I could hear the switch "flip" in the GP relay and then the dash glow plug light came on. I found this confusing.

Any other ideas are appreciated. Thanks
JT

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JT
1991 350SD 216,000

A .1 reading, or even a .3ohm reading really doesn't show enough resistance to be going through a good glow plug. Usually a reading of .6 to 1.1 or so indicates an OK glow plug.
One lead on a good ground, other lead either on wire from relay plug to glow plug, or on tip of glow plug, right?

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Thank you Jimmy. Your response nailed it. I tried another setting on the meter and 5 GPs read the same but one was way off. Fortunately for me it was the six cylinder GP, the easiest to replace! It's done and I'm a happy man.
JT

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JT
1991 350SD 216,000

A 0.1 would indicate limited resistance, right? So, would not actually build up heat .... the thread at http://www.peachparts.com/shopforum/showthread.php?t=174871 had interesting inputs in that many feel the resistance test itself is not a clear enough indicator - and that they like to test the plugs with full 12V current using cables from a battery - and, some noted the plugs' resistance likely changes substantially under full power.

After replacing my one failed GP (same story as yours with the light not coming on prior to start but coming on afte start - was my #5 and it was shorted vice low resistance), mine starts normally, and the light comes on and then goes out normally, but is still rougher than I would like - smooths out after a couple minutes, but I would be willing to bet some of the other plugs are not heating as well as they should.

When I next find myself with manifold removed or with extra time, I'll pull and full power check all my GPs - sounds like this is the only way to ensure they are working as they should.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg