Fuel pressure
checks
NOTE: These are my notes from a generic
fuel injection book. Readings are approximate. I have not done these
procedures, but they sound reasonable to me. Corrections and updates would
be appreciated.
You will be working
with gasoline, the most dangerous common substance on the planet.
Vapors can ignite from a spark or ember several feet away from the source of
gasoline and it doesn't just burn, it bursts into flame explosively. Don't
screw around. Be safe. THINK. It's best to have an extra set
of hands and an extra brain around - preferably an aware one. A fire
extinguisher is an excellent idea, too. Vaguely
related side trip.
- Obtain the following:
- 5/16" barbed brass joiner fitting
- 5/16" barbed brass tee
- three 5/8" hose clamps
- 0 - 100 psi gauge
- high-pressure hose sufficient to connect
gauge to tee
- Relieve the fuel pressure
- loosen the gas cap
- remove the fuel pump fuse
- crank engine until no firing
- re-install the fuel pump fuse
- Install the tee and gauge
- Cut the inlet line
- it runs the width of the fuel rail
and connects to the top right side of the rail as viewed from the
front of the car
- Install the tee in the line
- Install the gauge to the tee
- Disconnect the vacuum line from the fuel
pressure regulator (top left of fuel rail, as viewed from the front) and
plug the line
- Start the engine and read the pressure at
idle
- fuel pressure should read approximately
35 psi
- Reconnect the vacuum line to the pressure
regulator
- pressure should drop to approximately 30
psi
- if no difference, the pressure
regulator is bad
- if significantly less than stated pressures -
- SLOWLY pinch the fuel return line (left
side of rail as viewed from front, exiting from the bottom of he rail)
and see if the pressure rises to at least 35 psi (do not
exceed 80 psi)
- if so, the pressure regulator is bad
- if not, the pump is probably bad
fuel delivery
- If significantly greater than stated
pressures -
- cut the engine off, bleed fuel pressure
off as before, remove the return
line from the bottom of the fuel rail and connect a length of line
from the rail outlet to an external container (1 gallon minimum, to
collect the gasoline)
- Restart the engine and check the pressure
(stop engine quickly to avoid pumping more as than the container can
hold)
- pressure correct?
- fuel return line is blocked
- pressure still high?
- pressure regulator is bad
When finished, disconnect the tee & gauge
assembly and reconnect the fuel supply line using the barbed connector and two
clamps. Make sure the fuel return line is securely installed.
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