Thread: Fuel rail pressure for 3.5

ign on but engine not running might result in lower voltage on battery hence lower performance of the fuel pump, hence incorrect pressure in the rail. i bet the best way to provide no vacuum condition is to remove the pipe from the manifold and plug it on a bolt - to prevent extra air to the manifold.

i would say, you need some higher pressure in the rail for your turbo setup (vs usual atmo intake). or, better, get another fuel map. do you use stock efi or some aftermarket model?

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I re tested yesterday as it was the gauge leaking fuel

Engine running it was About 40 psi then with no vacuum it was 30 psi

I will replace reg and set pressures at these levels initially and see how I go

The fuel pressure regulator has a vacuum input to ensure that the fuel pressure is constant compared to the air "pressure" in the manifold.

if you have a turbo blowing say 5PSI this has to be accounted for when setting a fuel pressure.
Most turbo engines run at higher fuel pressure than non turbo so that the pressure remains high enough for fuel atomisation during full throttle.

I would run a higher pressure than you propose eg you propose no vacuum eg atmospheric at 30 PSI. If you have 5PSI boost then it should be 5PSI Higher. You may end up rich at part throttle but factory turbo engines have unique maps to take account of this.
Regards Philip A

Thanks phil but the truck is supercharged not turbo - is that an issue in terms of your advice?

Thanks phil but the truck is supercharged not turbo - is that an issue in terms
of your advice?

No same same
You should really do it on a dyno to make sure you don't go lean with boost.
Regards Philip A

Ok thanks - given it runs ok now except it stalls at low revs when engine warm at worst moments (ie on brakes down hill) I think I will set it at same levels initially then dyno it later once on road

Then might increase say 5psi and see how runs

It depends whether it is a flapper 3.5 out of an old RRC or 14CUX 3.5 out of a early Disco 1.
The flapper injection had injectors with little pipes on top and these are really hard to find replacements for, although I read somewhere a while ago that Nissan 3.0 as per Commodore fitted.

If a 14CUX then the sky is the limit . The OEM injectors are Lucas and are black with a green band on them. Thye plug into sockets in the fuel rail with O rings.

They are old fashioned now and can be directly replaced by Bosch Gen11 Yellow with 4 laser cut holes as fitted to Mustang 4.6 and readily available on Ebay.
Regards Philip A

Thanks guys
- I replaced the reg and tested old before I did. Also noted amount of screw in on the adjuster.

Currently set at about 41/42 psi no vac and 34 psi with vac connected at idle

See how it run next outing. All o rings on connectors stuffed - one leaking.

Might not have been diaphragm in reg - not sure.

Found one fuel rail to injector hose the hose clamp not on hose - sitting on manifold - must have been missed when installed. Fuel leaking on manifold at that point. That won't be helping.

In process found thermostat housing leaking at bottom - lucky find - wonder why was slowly loosing water.

Needs a good run to check all this has fixed hot idle stalling! Fingers crossed.

Skiboy