HDi mod. Plausible or a bit of bully?

drpau · Post by **drpau** » 02 Dec 2005, 22:36

I stumbled across a 'modification' while I was browsing another forum and it said that on the HDi engine, the fuel injection pump has 2 pistons that work at low revs and a third which comes in to play as rev's rise, apparently if you unplug an orange connector from the top of the fuel injection pump then this 3rd piston is enabled at low revs and therfore the car feels more responsive at low revs. Anyone heard of this, Im a bit sceptical myself..an old wives tale? Surely disconnecting a connector is not a good thing?

CHeers

Paul

Post by **DHallworth** » 02 Dec 2005, 22:51

i've heard of this toooo, i actually know somebody who did it on another forum, and he said he noticed no difference, i aint got round to unplugging mine yet.

David.

fastandfurryous · Post by **fastandfurryous** » 02 Dec 2005, 23:30

I think you'll find that revs have nothing to do with the actuation of the third pump piston. In normal operation all three pistons are used, but if the system goes over-pressure., the third piston is de-activated to reduce the amount of fuel returned from the fuel rail, and reduce the load on the pump and belts.

making the third piston operate all the time will simply increase the amount of fuel returned from the injection rail, and incease the pumping losses on the engine. Kinda pointless....

wheeler · Post by **wheeler** » 03 Dec 2005, 13:47

it is actually directly proportional to engine speed.when idling the pump operates on 3 pistons.from 2/3 of full load up to full load the pump operates on 3 pistons.when not idling & below 2/3 of full load.the pump operates on 2 pistons.it also automatically onto 2 pistons if the fuel temp goes above 106 degrees C.
if you disconected it then it is likely that the engine managemet light would come on also.

fastandfurryous · Post by **fastandfurryous** » 03 Dec 2005, 17:57

surely you've just described it being related to engine load rather than speed?

Which would indeed make sense, as I'm sure that it matters not what the engine speed is, more the amount of fuel required.

bencowell · Post by **bencowell** » 03 Dec 2005, 21:03

I unplugged mine several thousand miles ago. Very little change really, but I have a powerbox.

Might put it back and see if I notice anything.

wheeler · Post by **wheeler** » 05 Dec 2005, 00:00

fastandfurryous wrote:surely you've just described it being related to engine load rather than speed?

which i would say is directly proportional to the engine speed.

fastandfurryous · Post by **fastandfurryous** » 05 Dec 2005, 02:15

How can engine speed and engine load be proportional? The two are independent variables.

it's entirely possible to have almost any load at any engine speed.

drpau · Post by **drpau** » 05 Dec 2005, 13:21

So to sum it then, its not going to make any difference unplugging it?

pugxpert · Post by **pugxpert** » 05 Dec 2005, 21:28

i would say you are definetly making it worse at low engine rpm as by disconnecting it the 2 pistons in hp pump will will be working overtime,plug it back in asap