INLET
STRAINER
FUEL
RESERVOIR
FUEL
LEVEL
SENSOR
FLOAT
Fig. 3-10.
In-tank electric fuel pump and fuel level sender assembly.
Chapter
C
: Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair
59
Low residual pressure can be caused by leaking fuel
lines, injectors, or cold start valve, a faulty fuel pump
check valve, or a defective pressure regulator.
Fuel Injection Volume Test
When a pump volume measure is specified, the sample
is taken at the fuel return line rather than at the delivery
pipe. Attach a length of hose to the return pipe and route
the open end into a graduated container. Operate the
fuel pump the recommended period of time and com-
pare the quantity of fuel delivered to specifications.
Most systems deliver a quart, or liter, of fuel in less than
30 seconds.
Fuel Pump Replacement
A mechanical fuel pump cannot be repaired and must
be replaced if defective. Some electric pumps can be
repaired, but most are replaced. Use the following pro-
cedures as general guidelines to replace a fuel pump.
Mechanical Fuel Pump
Prepare for pump removal by disconnecting the battery
ground cable to prevent accidental arcing, and by loos-
ening the fuel filler cap to relieve any pressure. Also re-
move or reposition any parts that prevent access to the
pump. To replace the pump:
1. Disconnect and plug or cap all fuel and vapor lines
from the pump.
2. Loosen the pump mounting bolts.
3. Rotate the engine by hand until the pump pushrod
or rocker arm is resting on the low point of the
camshaft eccentric.
4. Remove the mounting bolts and lift the pump from
the engine.
5. If the pump is driven by a pushrod, remove and in-
spect it for wear. Use a straightedge to check
straightness; replace as needed.
6. Clean all old gasket material from the engine.
7. Install the new pump on the engine and tighten the
mounting bolts to the specified torque value.
8. Attach the fuel and vapor lines, reinstall parts re-
moved to gain access, and connect the battery
ground cable.
9. Install the filler cap. Start the engine and check the
system for leaks.
Electric Fuel Pump
Electric fuel pumps are usually located either under the
vehicle or inside the fuel tank. Some systems use two
pumps, one of each type. The in-tank pump provides a
constant stream of fuel to supply the main external
pump. The main pump delivers a high-pressure fuel
charge to the injectors. For all systems, be sure to re-
lieve fuel injection system pressure and disconnect the
negative battery cable before opening fuel lines. The fol-
lowing procedures are provided as general guidelines
only. Refer to the Service Manual for specific instruc-
tions.
In-Tank Electric Pump
Most late-model vehicles have an in-tank electric fuel
pump, figure 3-10. To access an in-tank fuel pump, the
fuel tank may need to be removed from the vehicle. Typ-
ically, the fuel pump is incorporated with the gauge
sending unit and is replaced by removing the sending
unit retaining cam ring. Loosen the cam ring with a
spanner wrench and lift out the assembly. Some pumps
are a separate unit, but it will also be installed with a re-
taining cam ring.
Before removing the retaining cam ring, clean the area
around it to remove any dirt that might fall into the tank.
Remove the pump and level sender assembly from the
fuel tank. In most cases, the entire pump, filter, and
gauge sending unit is replaced with a new assembly. If
the pump is a separate unit, be sure the hoses con-
necting the pump to mounting flange fittings are in good
condition. Some manufacturers recommend that the
rubber hoses and clamps be replaced whenever the
pump unit is removed from the tank, and that the pick-
up strainer be replaced as well. Always install new gas-
kets, seals, or O-rings when replacing an in-tank pump.
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