04-02-2014, 12:42 PM
The HP pump in a CP1 system requires pressurised fuel supplied to it - it has essentially no suction on the pump - soon as it starts dropping the pressure on the inlet side to the HP pump, it'll struggle to make pressure. That's why the CP1s are SO sensitive to the LP pump failing/going round a corner hard.
The problem is also exacerbated by the fact that the CP1 pump will move it's full amount of fuel into the inlet side of the regulator at all times. This is a problem with the early CP1 design - it means that it heats the fuel a lot, it's pumping closer to all of it's fuel through the body of the pump to high pressure, but then mostly bled off by the regulator.
That ALSO means that it's moving close to it's full quantity all the time, so it gets through fuel at a rate of knots - combine that with the fact that the LP pump often can't suck fuel up when you NAIL it round a corner, it's moving a lot of fuel, so air gets picked up easily, soon as a bit of air gets picked up, it then drops the pressure in the fuel filter housing, therefore the pump starts to starve of fuel, instantly dropping the rail pressure.
This is why I reckon these should be accompanied with a swirl pot in the engine bay - you only remove one problem by putting in a bigger lift pump, that's the supply issue when you stamp on the throttle and the rail pressure goes up - nail it round a corner or continuously demand big injections, you're still likely to struggle for fuel after the filter housing.
IMHO you should have:
Very poor diagram I know... But hopefully that explains what I mean...
Lift pump from the tank, into the swirl pot, another lift pump feeding fuel straight into the inlet of the CR pump, regulator for the CR pump bleeds off through a fuel cooler back to the swirl pot (or back to the tank, whichever you prefer - tank may be better to prevent any restriction on the return side) injectors bleed back off into the swirl pot (or tank..) also. You can change that round if you find you're not getting enough cooling of the fuel as an average, you want it slightly warmed which mixing it into the swirl pot should do nicely, if you cooled it on the inlet the HP pump I think you'd end up overcooling it and creating more ignition delay.
For the record, this is what the CP3 pump changed, the CP3 pump has it's own 75psi regulated gear pump internally, so you pump fuel to the inlet to the gear pump, then the pump is pressurised by it's own "feeder" pump internally and regulated before the HP pump to prevent fuel overpumping/heating.
The problem is also exacerbated by the fact that the CP1 pump will move it's full amount of fuel into the inlet side of the regulator at all times. This is a problem with the early CP1 design - it means that it heats the fuel a lot, it's pumping closer to all of it's fuel through the body of the pump to high pressure, but then mostly bled off by the regulator.
That ALSO means that it's moving close to it's full quantity all the time, so it gets through fuel at a rate of knots - combine that with the fact that the LP pump often can't suck fuel up when you NAIL it round a corner, it's moving a lot of fuel, so air gets picked up easily, soon as a bit of air gets picked up, it then drops the pressure in the fuel filter housing, therefore the pump starts to starve of fuel, instantly dropping the rail pressure.
This is why I reckon these should be accompanied with a swirl pot in the engine bay - you only remove one problem by putting in a bigger lift pump, that's the supply issue when you stamp on the throttle and the rail pressure goes up - nail it round a corner or continuously demand big injections, you're still likely to struggle for fuel after the filter housing.
IMHO you should have:
Code:
--------------------------------------|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|
TANK>>>>>>lift pump>>>>>>>>>>>>> SWIRL POT >>>>>>>>>>>lift pump>>>>>>>>HP CR PUMP>REGULATOR>>>>RAIL>>>INJECTORS
|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|<<<<<<<<<<<<<<<<<<<<fuel cooler<<<<<<<<<<<<<<<<<|Very poor diagram I know... But hopefully that explains what I mean...
Lift pump from the tank, into the swirl pot, another lift pump feeding fuel straight into the inlet of the CR pump, regulator for the CR pump bleeds off through a fuel cooler back to the swirl pot (or back to the tank, whichever you prefer - tank may be better to prevent any restriction on the return side) injectors bleed back off into the swirl pot (or tank..) also. You can change that round if you find you're not getting enough cooling of the fuel as an average, you want it slightly warmed which mixing it into the swirl pot should do nicely, if you cooled it on the inlet the HP pump I think you'd end up overcooling it and creating more ignition delay.
For the record, this is what the CP3 pump changed, the CP3 pump has it's own 75psi regulated gear pump internally, so you pump fuel to the inlet to the gear pump, then the pump is pressurised by it's own "feeder" pump internally and regulated before the HP pump to prevent fuel overpumping/heating.
