To whom it may concern and perhaps will help someone trying to isolate if the fuel pump is indeed faulty or not. Further to my 1st post investigations regarding this thread, I recently carried out some tests on a new (pattern) and original fuel pumps, I also took readings at different positions on a 1.8T to clarify things in my mind. BTW, the engine on this 1.8T goes like a scalded cat and there is absolutely no hesitation with either pumps fitted.
Another thing that has always puzzled me was why does the 1.8T need a higher pressure system compared to the NASP. Well apparently its all to do with manifold pressure when on boost. If there was not enough pressure in the fuel rail there is potential for the injectors not to dump their atomised fuel into the manifold, hence the reason the higher pressure system is specified. I guess that a NASP fuel pump may work (perhaps changing the regulator on the filter housing to 1.8T 4.55bar rating) but at higher revs one may start to get fuel starvation issues.
Anyway. If one follows RAVE instructions to the letter the fuel test should be made with the engine running, 4.3bar should be seen, however given that there is a damper (regulator) at the end of the fuel rail which is rated at 3.5bar, I cannot understand how RAVE can obtain quote that value? This is where I believe RAVE is incorrect. Typically in a number of 1.8T models I have noted 2.8bar at idle, and with the vacuum hose removed from the damper (regulator) you get about 3.2bar with engine running. In my opinion testing with the damper (regulator) on the end of the fuel rail is flawed, and a fuel pump which has got marginal output of say 3bar would not be picked up in the pressure test from the shraeder valve on the fuel rail.
The correct way to establish if you fuel pump or indeed the filter housing is intact and not backed off is to disconnect the fuel line in the engine bay and run a pressure gauge directly bypassing the engine bay fuel rail damper (regulator).
Original pump reading engine at idle, vacuum fitted to regulator note 2.8bar reading, taken from the schraeder valve:
Original pump, reading 4.6bar taken as ignition is switched on before it cuts out, and directly from disconnected fuel hose. I don't know what the original MG Rover pump spec is when new, perhaps its higher? :
New pattern pump reading 5bar taken as ignition is switched on and before it cuts and directly from the disconnected fuel hose. (The fuel pump spec new is 6.55bar). Note the disconnected hose, the light blue plastic connector inserted straight into a made up pipe to the pressure gauge. I find it strange to obtain this higher reading of 5bar as there is a regulator fitted to the filter housing of 4.55bar, but perhaps the discrepancy is due to the high volume from the pump and the regulator not coping? I used an old fuel rail quick connect fitting to adapt to the pressure gauge:
Fuel rail damper (regulator) rated at 3.5bar:
System description
The filtered fuel passes though a 4.55bar regulator on the side of the filter housing on the near side of the vehicle it arrives at the fuel rail where the damper 3.5bar (regulator) irons out any spikes as each injector is opening to maintain a constant fuel pressure under all conditions at the injector, more so important for turbo models with high inlet manifold pressures.