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Oil barrier and lubrication in fuel injection pump is subject to 200psi(13 bar) at injector open and the low pressure fuel gallery is tested at 3 bar when the pump is assembled. There are no seals that could be old or brittle either. I just had my injection pump apart after running two years with 38psi(2.5bar) and there was zero sign of wear. It went back together with the same elements. From a vapor lock (fuel boil) standpoint this system was always a dog. Bosch put Band Aids (Plasters) on it from day one. The fuel enrichment solenoid, the start assist kit, the outlet fitting change and at the end of production the ball check valves. This system was bad when gasoline was predominantly gasoline but with the mix of things added to fuel these days it is even worse. You don't need to run 38psi (2.5 bar) as I did but 20 psi would be plenty of pressure provided you could find a regulator / accumulator that would work at 20 psi(1.5 bar). That would give you a better fuel shot when cold and would be high enough to keep the fuel in the lines from boiling out.I just did the reasearch.This pump:Pierburg 7.21287.53.0This regulator:Bosch 0 280 160 001Mount both on a bracket in the original pump location so the pump cover covers it then route the return line into the fuel pump cover to the side port on the regulator. The bottom port with the threads is the outlet back to the tank. If you mount the regulator on it's side with the inlet facing down it will act as a small accumulator to allow some leakage from the check valve or injectors. connect a gauge where the cold start line connects to the fuel hose assy and set the regulator to 1.5 bar. Problem solved. If not I would creep up to 2 bar.Pierburg make a good pump. I just replaced the original one in my 2002 BMW with 150,000 miles on it. It was still running.
...It seems like a different material than the original...