Okay, folks, some new information on this.

I was able to successfully reproduce the problem with the vacuum supply to the shutoff mechanism COMPLETELY disconnected. Was making a trip home this weekend; 2 straight hours on the interstate at ~75 mph. Took the off ramp and threw it into Neutral while doing about 60. Watched it drop like a rock straight to zero. Cycled the ignition (still rolling), hit the starter, it cranked within 1 second and ran normally the rest of the day. For this experiment, the vacuum line that normally supplies the pump shutoff was instead supplying the MityVac gauge - which didn't budge.

So... whatever's causing this isn't related to the vacuum shutoff.

Next experiment I need to try? Could a dying ELR produce such symptoms? I've never looked at the OVP, is there any chance it's related?

I'm desperately fishing for theories here before this thing decides to do that to me in traffic one day and gets me stuck under a changing light cranking on the thing...

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL