The Bentley book says to test fuel pressure to hook pressure gauge to fuel rail, reinstall intercooler and start engine. The spec should be 50.8 + or – 3PSI. When I first turn ignition on the pump primes and comes right up to 51 PSI, after starting the engine it drops down to 42 PSI. I have changed the fuel filter and pump but still getting random misfire starting at about 2000 rpm. I have changed plugs and plug wires just in case but the fuel pressure drop still has me puzzled.Does anybody know if this is normal?

Thanks in advance for any help that can be offered

Oh ya it is a 2003 S no mods and about 92,000 fun filled miles

 

Have you checked spark at all cylinders to rule out the coil?

 

That is healthy fuel pressure gauge behavior. If it did not drop when starting, then suspect the fuel rail pulse regulator.

 

My rail pressure is the same, and I have misfires only in 4, 5, and 6 trying to full throttle accelerate from low speeds, in the range of 2000 - 3000 RPM. No codes.

 

Thanks for your suggestions. I picked up the coil pack from AutoZone but had to modify the mounting bolts (remove the metal sleeves). It ran worse than it did before; good news is that it produced a new fault code, P2304. One of the possibility causes is a short in power wire to the coil pack. Better news is that sure enough the insulation was rubbed off all three wires at the point where the wire tie holds the harness in place about a foot away from the coil plug. Fixed the wires and it runs great. Had I not replaced the coil it could have been forever finding the true cause. The education was not a free one but I have new parts that were close to their life expectancy anyway. Hopefully this will help someone else down the happy road.