Dyno shop in okc area

[Rawze]

(02-10-2023 )Rockinbexpress Wrote:  Rawze what sticks out to me the most is that the fuel pump actuator is always drawing more current then commanded. Curious what everyone thinks

Every bit of those fuel pump numbers and ranges are within spec and look pretty normal to me. It is not the pump as far as I can tell... and NO, as far as the fuel pressures, etc. go .. .. it is not surging.. it is working exactly as intended.

The fuel pump is not regulated like a typical low pressure hydraulic system would be. The fuel pressure will never be a steady set value, it is not designed this way because it cannot be designed this way. This would mean it would have to have a ball-spring regulator type of system .. however at 40,000 psi this is not going to happen without destroying the fuel itself.

It cannot be regulated via a ball-spring (steady pressure) regulator type system where the pressures are held steady. The fuel system on a common rail engine does not operate that way at all because a ball-spring (or similar, steady pressure) type regulator would heat the fuel to several hundreds of degrees as it bled thru the valve half way open with tons of resistance behind it and this would cause the fuel to overheat and break down at those exceeding high pressures. . It cannot operate in this manner at close to 40,000 psi.

The fuel system is designed around what is know in the hydraulic world as a "Bypass Charging System" instead so that the fuel does not overheat by having to pass thru partially open regulating valves at those extreme pressures. This type of system is of text-book hydraulics 101 design and nothing unique or special at all, and is the de-facto standard for high pressure systems.

Bypass-charging systems are the norm at those higher pressures. They operate so that the pump provides 100% full pressure to the storage device (the fuel rail in this case)... until the pressure reaches a desired setting. The pump is then completely shut off .. all load removed.. "bypassed", i.e.> 100% switched off (by a bypass valve that makes closes off the rail and sends the pump into neutral with no more load on it at all.. until the fuel rail looses a set amount of pressure. Once the pressure drops below a threshold.. then the pump kicks back in only enough to top it off.. and then goes back quiet... and the cycle repeats as necessary depending on how much fuel the engine is consuming.

It kicks on and has a high load placed on it.. then kicks out again until the pressure in the rail falls off below a certain point.. then repeats. -= That is how it is supposed to function and that is how it is designed. When it kicks out.. it will usually be slightly above the desired pressure,.. and it will not kick back on again until the pressure has dropped a bit below the desired pressure, so that it does not cycle on/off too often and wear itself out. This means that there will be a whole varying range of pressure readings both a bit above and below the desired pressure when it is operating normally... cycling up and down a bit as fuel is supplied, and then consumed by the injectors or system.

Your numbers that you posted up there reflect this and they look fine... and look like they are all in spec as far as the fuel pressures go any ways. The allowance I think is about 350bar in total.. and you are under that at only 250bar (looks about right by the way) by quite a bit it looks like.

so if you think that the normal operating cycle of the fuel pump and how it operates is your issue,... then you are mistaken.

If the engine is surging erratically, then it is not likely the fuel pumps itself's fault... especially if it has been taken apart, inspected, and the plungers, etc tested + checks out properly.

How many mg/stroke does the engine consume at idle?. cold?... and warmed up all the way ???? - This would be far more telling of if there is too much load on the engine or not.