Figured it out!! Injector number 5 was completely plugged!!

From one of my last posts above, you can see I isolated it to cyl #5 by pulling the plug wires on each cylinder. I knew it must be injector related because I had a good spark on that cylinder. I pulled the injector out (very easy) and threw it into my pop tester that I use with my diesels. The injector looked very nasty and dirty (nearly 20 years old, what do you expect?). After pressuring it to 100# it was barely dribbling. Finally at about 400# of pressure, it popped and blew out whatever was plugging it. After it was unplugged I got a decent (but not great) spray pattern at something less than 100#. I also pulled #6 injector and put it in the tester and it seemed OK, and then I swapped the two on re-installation, just in case the problem persisted, I wanted to see if it would move to the other cylinder. Fired the car back up and she is as smooth as ice!! That M103 is a smooth engine!!

So the new plugs, the coil, the O2 sensor, the wires, the OVP relay - none of these were it, although I learned a bunch in the process. I swear that after probably 3-4 hours of reading aricles on this forum and others, I never read anything about a completely plugged injector on a M103.

Thanks for all the input, and many of the ideas I got from others helped me to finally figure it out. StormyC88's idea to pull each wire to find the dead cylinder was a key diagnostic step that I passed over too easily early in the process. Also, being able to pressure up my injector with my pop tester (most folks probably don't have one) was another key.

Since these injectors seems to have poor spray patterns, and since they dribbled a bit even after they would pop, I am going to replace them all. Will cost less than $200 and I believe that it will make a pretty big difference in fuel economy to get those restored to new condition. And the installation is so easy.

Thanks again to everyone who gave me assistance.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K