Fuel System Testing: Notes

The fuel system tests outlined in the fuel system diagnostic flow chart and detailed procedures (Tests 1-8) provide a systematic approach to determining whether the fuel system, from fuel pump to fuel injectors, is functioning as intended.

For the engine to operate as designed, the fuel supply system must deliver fuel at the proper pressure with adequate volume and maintain pressure after the engine (and fuel pump) are turned Off.

In addition, the fuel injectors must deliver the precise quantity of fuel at exactly the correct intervals with no leakage of fuel when the injector is turned off.

The battery of tests outlined in the FUEL SYSTEM DIAGNOSIS - FUEL SUPPLY CHART are designed to evaluate all the performance characteristics. Symptoms or complaints related to the fuel system include:

Hard starting.
No start (Hot and/or cold).
Extended cranking.
No/Low power.
Start/stall.
Rough idle.
Poor acceleration, stalling, stumbling.
Misfire/backfire.
Rough/erratic idle.
Surges/hesitates.

Diagnostic trouble codes associated with fuel supply problems include P0171 and P0172.

NOTE: The performance of the fuel pump (pressure and flow) is very dependent on supply voltage. The voltage must be above 12 volts when running any of the diagnostic tests. Published test specifications cover the range of system operation from 12.0 to 14.0 volts, but are biased towards the lower voltages (12.0-12.7 volts) since all tests are run with the engine Off. All accessory loads should be Off when running any tests (DRL's, interior lights, radio, etc.) to provide maximum available voltage for the tests. If voltage is below 12.0, battery must be charged before running tests.