g p motor sport

hi there I have 2 questions about fuel pressure on my classic
fuel system is Rcm pump feeding Swirl pot then Bosch pumps 044 type feeding fuel rail, an6 teflon hose through car to pressure regulator 660 injectors fitted . pressure gauge at rear also Question number one the pressure is 4 bar ,is this too high. When the engine is switched off the fuel pressure drops to Zero . Question number two is this normal for subarus . I was thinking that there should be residual fuel pressure for at least some time
any help would be helpful
thanks geo

arthur.d

where exactly on the fuel system are you measuring pressure?
is it the very last point before an aftermarket fpr..
pressure on a 1-1 ratio fpr will rise as much as your boost via the hose attached-ie another 2 bar if you run 2 bar of boost to 6 bar total as i understand it-which your pumps must be capable of or the system will not provide efficient fuel pressure to the injectors
the system will hold some residual pressure in the line from the pump to rail[one way valving on pump/s but the 4 bar is the running pressure provided by the pumps pumping the fuel through the tiny gap created by the fpr....

trevsjwood

iTrader: (2)

I have an identical system but on a newage. I run an aftermarket FPR which has the pressure gauge attached, also run an electronic gauge inside car, again plumbed into the FPR. I find pressure drops quickly when car is turned off. Regarding boost pressure, my car runs at 3.7 bar fuel pressure at tickover, this as mapped, and then + whatever boost the turbo is making, so full chat +1.6bar = 5.3bar fuel pressure.
When I installed my Bosch external/swirlpot, fuel pressure increased to nearly 4bar, I just tweaked it back to 3.7. I would have thought 4bar was ok providing that's in the map and not as a result of changes made unseen by your mapper.
hope this helps
Trev

arthur.d

another thing to remember is that there is vac at idle[half a bar maybe] negative pressure,so although we all set it pipe off/plugged at say 3.5 bar for a high performance engine -that changes a little as we raise the idle to have zero vac/boost
some folk recommend setting the fuel pressure with pump on,engine off for a more representative reading of actual fuel pressure