Is there any sign of leakage around the delivery valve seals on top of the injector pump?

What you are describing is almost always a fuel problem...a leak somewhere...can you look to see if there are any air bubbles in the lines while someone else revs it?

I'd replace that shutoff o-ring...even if it was done in 11/05 it could be leaking again. Mine did after less than 2 years, just after they started selling ULSD here.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz