I'll greep out on to, for me, a shakey limb... No experience with the
European offerings and I work in PSI rather than bar....
IIRC, 1 bar = 1 atmosphere (or 14~15 psi). Now.... *most* of Fords port fed
fuel injectors work in the 40 psi range - a pound here or a pound there
isn't the end of the world. All of these have some sort of interactive fuel
pressure regulator. Here's why....
A fuel injector nozzle is designed to deliver it's best pattern at a
specific pressure drop across the nozzle. This is why fuel pressure at idle
(high vacuum) is lower than fuel pressure in high throttle angle/low vacuum
situations.... it's all about maintaining that "constant pressure drop".
For a fuel pressure test to have any real meaning, we need to conduct the
test when the concern is evident. Many faulty pumps can deliver the required
pressure at idle, yet fall flat on their faces during a high fuel
requirement condition (higher gear, higher rpm, high throttle angle).
Roughly, the same thing applies to CFI type units... those where there is a
single injector.throttle body assembly situated where a carburettor (isn't
it nice that I know how to spell it correctly?) would have been. The fuel
pressure regulator on these units react to atmospheric pressure rather than
manifold vacuum. Again, the idea is to maintain a constant pressure drop
across the injector and, once again, the fuel pressure needs to be read when
the concern is happening.
FWIW.... I have yet to see any fuel pumps that can be called robust.... they
don't like running out of fuel and they don't like pumping against
restricted filters for any length of time... I don't know how many times
I've seen fuel pumps fail within just a few miles of filter replacement
where the old filter was plugged near solid...
Words of caution... when checking fuel pressure while driving... do NOT
bring the guage into the cabin.... the last thing anyone needs is for a high
pressure fuel leak to develop in an enclosed space. When using a mechanical
guage, bring the guage out to the windscreen and use duct tape (also known
as gaffers tape) to affix the guage to the glass.
thanks very much for such a long reply!
40 PSI = 2.75 BAR.
mine is currently at 43.5 PSI (3 BAR)
The car runs good, little stuttering (will try ultrasonic injector
cleaning), but mpg might suffer due to fuel pressure being a bit high (if it
you gave me some new thoughts to consider about the fuel pump...
I gave thought to route mechanical fuel pressure gauge to cabin... good
thing I gave it up, because while I was drive-testing the pressure, one
clamp disengaged spraying something like half a galon all over the engine
... if it was in cabin the car would be a smelly mess for a long time...
I was lucky the spark plug cables weren't faulty or the spilled fuel would
I doubt whether a bit of excessive pressure will affect gas mileage, or
anything else for that matter. Your car has an oxygen sensor, and the PCM
will 'learn' the correct fuel trim for the pressure, as long as it is within
the adjustment range. Injector pulse durations will simply be a bit shorter
than nominal, and that's it.
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