Well, the new injectors did the trick! The start/stall/start/chug-chug/run behavior is gone. As best as I can figure, the injectors were leaking fuel into the cylinders, which relieved the pressure in the system. On the first start attempt, the engine would fire on the leaked in fuel, but would stall because there was no pressure in the system to open the injectors, The chug-chug came from the fuel laying in the cylinders causing a "flooded" condition. Eventually, continued cranking would build up enough system pressure to fire the injectors, the extra fuel would go out the exhaust, the plugs would dry out and the engine would operate normally. I don't know if this is right, but it sounds good to me. However, I'm open to alternate therories.

Changing the injectors was easier & cheaper than I thought it would be. It would be even easier if I did it again, as I know a few things about the process. All the parts cost $223 and change from Fastlane, arrived in one day (Atlanta to Northern Illinois) and after 6 months of struggle finally solved my starting problem.

A few tips that made the process easier:

1. Leave the clips that hold the injectors down, in place until your remove the fuel lines. I found it easier to get to the allen head bolts that holds some of the injectors in place by taking the fuel lines loose at both ends. In one case that required removing the EHA valve to allow me to turn the wrench.

2. I was able to slip a 17mm open end over the clip where the hex on the injector is to provide back pressure to loosen the fuel lines.

3. I had to use an allen wrench with a ball end to remove and replace the bolt on injector number 4, and it was tough getting the bolt to line up straight when I put it back in. The rest were pretty easy.

4. I used brake cleaner and an acid brush to clean around where the holders go into engine so that no dirt would drop in when I removed them. I'm glad I did, as though the engine is clean, it wasn't clean enough.

5. After it was all back together, and warmed up I had to reset the duty cycle, the reading had changed from 50% to about 75% and the idle was "hunting" up and down. Setting it back to 50% smoothed it out perfect.

When this happens on my "next" Benz, I'll start with the injectors and work the other way. Some of the old ones fit nice and tight, others slipped out easily. I'm sure there must have been vacuum leaks around the the really loose ones.

Hopefully this will help others struggling with the same behavior.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire