Fuel Pressure regulator Question..

Just trying to work out effect on Fuel pressure regulator (FPR) by not connecting the vacuum...

I have it set @ 40PSI with no vacuum....

...Thing is as I suck on vacuum pipe regulator drops pressure to about 30 PSI.

What I cannot get my head around is I though the 14CUX need approx 40PSI for it to run...

So whats the point of reducing pressure under vaccuum?

I figured it was meant to increase!

Just to add to that I have disconneced vaccuum completely and it is running at 40PSI all the time, is there any detrement to that?

The purpose of the regulator is to keep the relative pressure constant- if the manifold pressure is lower, then the fuel pressure will also need to lower to deliver the same amount of fuel.

Not sure if I get it - I figured that as revs rise you would need more pressure to put more fuel in to keep up with increased demand...?

If your regulator is adjustable you should set it to 36-38psi with the engine off. Set it jut by flicking on the key so the fuel pump primes.

Fuel pressure does drop relative the inlet pressure so if you have 10psi inlet pressure your fuel pressure will drop by 10psi

If the vacuum pipe is off your regulator it will got to the max you set it at as it is seeing no vacuum pressure

What he said^

The engine does need more fuel as the revs (or load) increase, but it is not done by increasing the fuel pressure but by holding the fuel injector open longer - this is done by the ECU.

Think of it in terms of filling a sink, to fill a sink to a set level you can either open the tap a long way so the water comes out quickly, or you can open it a little way but leave the tap open for longer. Both will fill the sink to the required level. (if the water pressure were to increase whilst the tap was open, the sink would overfill as you'd get more water than you expect. You will probably have experienced this if someone is running water in another part of the house at the same time as you and suddenly turns a tap off - the water coming out of your tap unexpectedly increases)

Now imagine you can't actually see the level in the sink. If you didn't know how fast the water was flowing (because you didn't know what pressure it was at) you wouldn't know how long to have the tap open for. This is what the fuel pressure regulator does, it keeps the flow at a set level so the ecu knows that for a given time, the fuel delievered will be a set amount, irrespective of variations in atmospheric pressure (or vacuum)

Gotcha! So over fueling would follow with PFR running at 40PSI all the time?

Reason I started - me engine is misfiring when pulling away between 1500 & 3000PM, but fine stabing throttle on driveway.

As you may of gathered, I have retro fitted EFI to a carb engine, (I know NOTHING about EFI - I am a mechanic's guy!!!) and it is turning out to....... Testing!

Thanks

M

Yes, it would.

SORTED!!!!


See Running mega rich thread....

Turns out you need breather from head cover attached to the plenum....