Pontiac Fiero 1988 Service Manual page 599

6 E 3 - A - 1 6 DRIVABILITY AND EMISSIONS - F U E L INJECTION (PORT)
RETURN OWE
START VALVE
5-18-87
8-8-84
5S1288-6E
CHART A-7
(Page 1 of 4)
FUEL SYSTEM DIAGNOSIS
2.8L "P" SERIES (PORT)
Circuit Description:
When the ignition switch is turned "ON", the electronic control module (ECM) will turn "ON" the in-tank
fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving reference
pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after ignition
"ON" or engine stops.
The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system
pressure is controlled to about 234 to 325 kPa (34 to 47 psi). Excess fuel is then returned to the fuel tank.
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. Wrap a shop towel around the fuel pressure
connector to absorb any small amount of fuel
leakage that may occur when installing the gage.
Ignition "ON" pump pressure should be
280-325
kPa
(40.5-47
psi). This pressure is controlled by
spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure
is low (high vacuum) and is applied to the fuel
regulator diaphragm. This will offset the spring
and result in a lower fuel pressure.This idle
pressure will vary somewhat depending on
barometric pressure, however, the pressure idling
should be less indicating pressure regulator
control.
3. Pressure that continues to fall is caused by one of
the following:
• In-tank fuel pump check valve not holding
• Pump coupling hose or pulsator leaking
• Fuel pressure regulator valve leaking
• Injector(s) sticking open
An injector sticking open can best be determined
by checking for a fouled or saturated spark plug(s).
If a leaking injector can not be determined by a
fouled or saturated spark plug the following
procedure should be used.
• Remove plenum, and remove fuel rail bolts.
Follow the procedures in the fuel control
section of this manual, but leave fuel lines
connected.
<$ Lift fuel rail out just enough to leave injector
nozzles in the ports.
C A U T I O N :
Be sure injector(s) are not allowed
to s p r a y on e n g i n e a n d t h a t
injector retaining clips are intact.
This should be carefully followed
to prevent fuel spray on engine
which would cause a fire hazard.
Pressurize the fuel system and observe injector
nozzles.