I have a 93 300D and last month my orange preglow light stopped working. At the same time the car started to have a very rouph start. I took the manual pages and working through their diagnosis came to the conclusion that the preglow relay was bad. No prob, I got a new one, $150 and now the orange light works, but the car still starts rough. Black smoke, uneven idle for the first five mins of running the car. I went back to my trusty manual pages and did the test procedures and am not clear on next steps. The preglow relay is producing 12 volts. From the connetor at the preglow relay that runs to the glow plugs I was getting 0.42 ohms resistence on 4 of them, on the 5th I got 0.55 ohms resistance. When I took the 5th plug out (wow what job that was!), the plug looked fine, some degradation of the tip, but not bad, the resistance was 1.5 ohms.
My instinct is to replace the glow plugs, but at $80 my insticts have weakened. Plus, I think I would have to take off the intake manifold to get to the little buggers, is that right? Any thoughts on what the possible problem could be? How do I do a further diagnosis? One step suggested is checking the current to the glowplugs, but there is no place to slip my ampmeter clamp, do I have to remove a bunch of the outer protective tubing and pull the wires apart? I hate to do that.
Comments appreciated.