Fuel Pump - Diagnosis

84chrysler6

Models


All Domestic Passenger Cars & Trucks


Subject


Fuel Pump Diagnosis


Index


FUEL

Date April, 1984


No..


14-30-84

P-1710-C
SYMPTOM/CONDITION

^ Long crank times or difficult to restart after a 20 to 30 minute hot soak.

^ Engine will exhibit a sag or stumble on hard acceleration (wide open throttle) when engine is at full operating temperature.

A faulty fuel pump will certainly have an adverse affect on vehicle driveability and performance, and may be the cause of the conditions described above. However, not all driveability problems are caused by faulty fuel pumps.

It should be determined that the fuel pump is defective before it is replaced.

If a faulty fuel pump is suspected, and there is no obvious problem such as an oil leak, fuel leak, or a noisy pump, then the diagnostic test outlined below should be performed.

Fuel Pump Diagnostic Test

1. Disconnect the inlet and outlet fuel line from fuel pump.

2. Connect a vacuum gauge (0-25" Hg. minimum range) to the fuel pump inlet fitting.

Using the starter motor, turn the engine over several times and observe the vacuum gauge. The pump should develop a minimum of 11" Hg. of vacuum, although readings as high as 22" Hg. may be seen. If the pump does not develop 11" Hg. of vacuum, it is defective and must be replaced.

3. Remove the vacuum gauge.

4. Connect a pressure gauge (0-15 PSI minimum range) to the fuel pump outlet fitting.

FIGURE 1:

Using the starter motor, turn the engine over several times while observing the pressure gauge. The pump should develop the pressure specified in Figure 1 for this application. If the pump does not develop sufficient pressure, it is defective and must be replaced.
5. Remove the pressure gauge and reconnect the inlet and outlet fuel lines to the pump.

6. Start the engine and check the pump and lines for leaks.

Other possible causes of fuel starvation are listed below:

^ Kinked or pinched fuel lines or hoses.

^ Plugged in-tank filter sock.

^ Plugged in-line fuel filter.

^ Water in fuel.

A faulty fuel pump could be only one of many causes of driveability complaints. Be certain the fuel pump is defective before it is replaced.


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