Dual speed fuel pump L67

[VX L67 Getrag]

Has anyone ever noticed how much difference there is especially in idle area for using a single speed fuel pump instead of dual speed?

With this car in tuning I'm getting around 18% too much fuel around idle areas & then just have to blend it in & guess roughly where the hi speed would kick in & leave those areas alone as a base starting point!

[Jayme]

ideally it shouldnt make a difference.... all its doing is reducing the amount of fuel recirulating via the return line as the fuel demand isnt as high at idle. the pressure at the injector should remain constant.

that being said I have no experience playing with them.

[delcowizzid]

nothing should change the reg should still be holding the same constant pressure at all times just the pump slows down to stop getting to much heat in the fuel it doesnt lower pressure.

[DanWA]

I have noticed zero difference swapping from ecotec pump to a genuine NOS L67 pump

[VX L67 Getrag]

Yeah that all makes sense, there must be another reason I need to take 18% out then, just strange as it has a new reg, cleaned l67 injectors & new pump (just not running the dual speed controller).

[delcowizzid]

pump too big for the reg?? tested fuel pressure?

[Holden202T]

yeah that's what I'd be doing, see if the pressure increases at the same points its going too rich.....

I know my situation is a little different, but I have recently setup 2 x 044's and when I tested them both on at idle it did increase pressure a fair bit, I assume this is 2 pumps feeding a 1/2 fuel line into the motor and the return line only being 5/16 ....

I set it to run the second pump on boost only and I don't see any spikes in rail pressure now!

[kojab]

ideally it shouldnt make a difference.... all its doing is reducing the amount of fuel recirulating via the return line as the fuel demand isnt as high at idle. the pressure at the injector should remain constant.

that being said I have no experience playing with them.

nothing should change the reg should still be holding the same constant pressure at all times just the pump slows down to stop getting to much heat in the fuel it doesnt lower pressure.

"Ideally" would be nice, "nothing should change" is positive but the reality is the fuel pressure will change in the rail if the flow and pressure of the fuel is increased by the pump due to a higher voltage/current being applied. The fuel pressure regulator is not like an electronic regulator/circuit which is very capable of maintaining a constant voltage with different loads. The fact is that if you fit a stronger pump or change speeds of a pump the fuel pressure will regulate but at a different fuel pressure in the rail. If two fuel pumps are used with the same fuel reg the fuel pressure increase is more easily seen as 202 has noted.

Putting it simply the fuel reg still regulates but at a different pressure if the fuel pump output is changed. We all know it changes with different engine vacuum and this is why it is not easily noticed unless someone is looking for it.

[0081(2)]

I also found that after I installed a new high flow pump I needed to remove fuel at idle.

[slewinson]

That is because the fuel pumps can push more flow than the regulator can handle, causing fuel pressure to rise. Replace the regulator with one that can handle higher flow and the tune will not change with pump flow.

Simon