My 300d will not start if it sits for 48 hours. My indy says that there is a check valve in the IP that prevents fuel leaking back that may not be working and thus permits a drain to the tank,and/or I have a small air leak in the fuel return line that permits air to displace fuel in the pump.

The car runs well as long as I use it every day, or at least start it and let it run for a few minutes....but let it sit two days, forget it. I have to try to start it about 10x then: it starts, runs at idle for 6-7 seconds, stops. An hour later, it starts, runs 10 seconds. I go through this routine which is a PITA as you can figure...

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71 220D 169K wrecked
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79 300SD (partswagen)
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70 220d (partswagen)
68 280s GASSER!!! under construction now
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69 250S newest project 54K