I just debugged a glow plug problem in my car that has been dogging me for awhile. I had a rough start at cold that appeared to be a glow plug problem. The lamp didn't light.

I did the ohm meter resistance test that is discussed in multiple threads here and all the plugs came in under 1 ohm. Also I hung a meter on one of the plugs and saw the relay put voltage to the plugs even though the light didn't turn on. A bunch of threads here said the light won't come on if one or more of the plugs is gone.

So on more reading, there are a few replies to glow plug posts saying you should light them off on a battery and look for the actual glow. At the point I was near concluding the GP relay was out and buying another, I decided better do what they showed on diesel giant and other threads here and actually glow the things. #1 read 0.9 ohms but wouldn't glow when hooked to the battery.

I swapped it out with an old one that did glow and now the GP dash light comes on again. The car doesn't have the raunchy start either.

Just thought I'd reinforce that the ohm meter test isn't a catch all. I've used it before and nabbed many burned plugs but I wasted a night playing with my GP relay, indicator light and harness because I mistakenly determined my GPs were good because they read low resistance.

I know this is mentioned here in some replies but I thought I'd say it again if it'll save some time and money for any of you.

Very good point, testing the resistance is an easy first step, but it can fake you out occasionally.

If my plugs read no resistance, open resistance, or anything but 0.6 ohms, I replace them. And, I replace all of them at the same time. The $50 is less than a tune up on a gasser, as with a gasser I also replace the dist cap and rotor.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

They will also read incorectly on a warm engine.