BenzWorld Junior Member
Date registered: Jun 2011
Vehicle: 1993 W140 500SEL- 90K miles White/Palomino, 1985 W126 380SE- 170K miles Grey/Black
Location: Detroit, MI
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Suspect that check valve in the fuel pump or a worn out fuel pump (may have low volume/pressure output- Do a routine test on the pump/ refer to pump performance specifications s for datai) or leaking fuel injector(s) because you're loosing pressure at cold start ups.
The fuel pressure regulator should be checked as well with an accurate vacuum tester- any vacuum leak down means higher regulated fuel pressure though- *from my experience. The regulator restricts at high vacuum and allows more flow at lower vacuum. The vehicle creates higher vacuum at closed or partially open throttle and no engine load, thus lower fuel pressure due to regulator response.
Is this the original fuel pump or aftermarket? Check for original part no.s. Generally though, these pumps are bullet proof, but they can have failures....