Above is a pressure and flow tester to on a Nissan Primera. The idle pressure was 270KPA and with the return line clamped was 480 KPA. With the vacuum tube removed from the pressure regulator the pressure was 320 KPA and with the engine off and let rest the pressure was 269 KPA. It was pumping 2.1 liters per minute.
Low fuel pressure can cause at first low power at top end and running lean, and if it gets worse it can make the engine stall or not start at all. This can be caused by a blocked fuel filter, line or pickup. or it could be a faulty fuel pump or pressure regulator.
high fuel pressure can cause the engine to run rough and cause excess black smoke from the fuel not burning efficiently.
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