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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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Discussion Starter #1
So I get in my car yesterday and start it up cold and it runs rough and stumbles like it's running on only four or five cylinders. Since I have a habit of how I start the car, I never really pay attention, so I ask myself, "Did I let the glow plug light go out or did I start it right up." Maybe that's the problem. So off I go and the rest of the day there was no problem. Today I get in and pay attention to everything I do. It's also about 20° warmer than it was yesterday. So I make sure I let the glow plug light go out and start the car. Same thing as yesterday - running rough and stumbling around on less than six cylinders - no real visible smoke though. So off I go and everything is fine on the rest of the starts after the car has warmed up. So I do a little investigating. Motor mounts maybe? Just replaced them about 40,000 miles ago and there is no noises or shaking in reverse, so it's not that. Check the fuel lines - no leaks and no air bubbles. That means it's likely glow plugs, but there is no check engine light or glow plug light on like there was when I had a bad glow plug before. So I pull out my ohm meter and sure enough one plug is reading bad. Five plugs are reading about 1.0 ohms and one is reading about 155 ohms. Not sure which number plug it is. I know they are numbered, but my eyes couldn't see any markings on the glow plug connector. The bad plug is shown below. Makes sense that it is probably #2 or maybe #5?


Looking at the glow plug connector from the steering wheel, this is where the bad plug is. Is that #2? Interesting that #2 was the plug that went bad on me about six years ago. Also interesting that the original plug went bad at 71,000 miles. It has now been almost exactly another 71,000 miles and it goes bad again. Coincidence??

So I now have to decide - do I replace them all or do I replace just the one bad one with one of the used good ones I have in my spare parts? I'm leaning to doing them all. What do you guys think?
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