Vacuum at Idle on 1.4 Micra

[Ihtisham Rauf]

Would anyone have any idea what sort of vacuum is drawn in at idle on a Micra?
I'm looking to get an electric brake vacuum pump installed, as the current setup of just drawing in vacuum from the cylinder 4 runner is not enough to fully power my brake servo.
Currently as a workaround, I have used the small vac ports on the individual throttle bodies from all 4 cylinders to provide the necessary vacuum to the brake servo, brakes are good now, but the car is rough on idle and low throttle, which makes sense as the car was mapped with the small vac ports on the throttle bodies capped off, yet I have now uncapped these, so essentially the car now has an air leak as its drawing in air below the the butterfly's.

So ideally, I need to cap the vac ports on the throttle bodies off again, so that the car is just as it was when I received from mappers. This would sort the 'rough idle and rough on low throttle' situation out but then brakes will be bad again.

So then I'd need to get an electric brake vacuum pump installed, this would be connected to a vacuum manifold, and from here, it would tee off to connect to the brake servo and the fuel pressure reg.

However, if the vacuum is vastly different from the natural vac of the engine, then surely this would alter the fuel pressure readings right? which would mess the map up on idle and low throttle?

So I'd ideally need to know the vac that the Micra engine provides on idle and low throttle?

Would anyone be able to provide this info please?

Thank you very much!

 

[frank]

about half a bar Ihtisham

 

[Ihtisham Rauf]

about half a bar Ihtisham

Thanks for the quick reply Frank,
But I've just realised that my method won't work, because to my understanding, if I connect the electric vacuum pump to the vacuum manifold, and from there, it splits off to the brake servo and fuel pressure regulator, then this would mean the fuel pressure regulator gets constant vacuum, rather than vacuum which varies with throttle.

Do you see any way that I could make the whole thing work?
Really appreciate any help, I'm a bit stumped on this as the FPR needs a vacuum that varies with throttle rather than the constant vacuum provided by the electric pump.

 

[frank]

yes the purpose of the vacuum reg is to balance out the vacuum pulling fuel out of the injectors at idle eh
how about some 1 way valves on your 4 barbs ?

 

[SuperUno]

Can you not use an electric servo, many diesels and turbo cars of the 90's had these as they produce little to no vacuum?

 

[Skinner_87]

you should have more than enough vacuum off one cylinder to power a servo. Are you using the factory manifold to servo pipe?

 

[Ihtisham Rauf]

you should have more than enough vacuum off one cylinder to power a servo. Are you using the factory manifold to servo pipe?

I’m not using the standard pipe. Tried earlier today and it’s actually nowhere near as bad as I thought.

 

[Skinner_87]

I’m not using the standard pipe. Tried earlier today and it’s actually nowhere near as bad as I thought.

I only mention that as i run a Skyline M/S on the standard micra break servo ran off cylinder 4 with the standard hose, never felt a lack of power.

Fuel reg is simply a vac feed T pieced from each runner then to the reg.

 

[SuperUno]

Piggy backing on your thread but.... is the Skyline M/S a direct fit ?

 

[Low Rider]

You're probably somewhere between 0.25 and 0.3 bar max vacuum at idle. It could be less but you haven't mentioned the cam profile you switched to from the 774 cams previously installed.

Having vacuum off one runner means you're lacking vacuum 'rate'. You'll still be able to pull the same total vacuum, (assuming you're ITBs are balanced properly), but you may suffer brake effort issues on multiple applications in traffic for example. It's better however to use all 4 from a balance perspective but it won't cause a leak. If you do have a leak, you should check all the vacuum pipes and fittings, seals etc carefully.

 

[Ihtisham Rauf]

Thanks to everyone for the advice, really helps