Fuel pressure test
Fuel pressure test refers to checking fuel-system pressure on the Pontiac Fiero.
A fuel pressure test is useful when diagnosing no-start conditions, hesitation, poor acceleration, lean or rich running, stalling, hard starting, and fuel-related diagnostic trouble codes.
Overview
The Fiero fuel system must provide the correct pressure and volume for the engine to run properly.
Low fuel pressure can cause lean running, hesitation, stalling, poor acceleration, or a no-start condition.
Excessive fuel pressure can cause rich running, poor fuel economy, black exhaust smoke, fuel smell, or fouled spark plugs.
Fuel pressure testing is especially useful when diagnosing Code 44, Code 45, and no-start problems.
Location
Image wanted: Photo or diagram showing where to connect a fuel pressure gauge on the Fiero. Ideally include the 2.8L V6 fuel rail Schrader valve and relevant 2.5L four-cylinder test location or procedure notes.
Fuel pressure test access depends on engine and year.
On the 2.8L V6, fuel pressure can be checked at the Schrader valve on the fuel rail.
On the 2.5L four-cylinder, the test method and access may vary by year and throttle-body injection configuration.
Always use the correct procedure for the specific engine and fuel system.
Safety
Fuel pressure testing involves gasoline under pressure.
Safety precautions include:
- Work in a well-ventilated area.
- Keep sparks, flames, cigarettes, and hot work away from fuel.
- Wear eye protection.
- Use a fuel pressure gauge rated for gasoline fuel injection.
- Relieve pressure according to the correct procedure before disconnecting fittings.
- Catch spilled fuel safely.
- Wipe up fuel immediately.
- Check carefully for leaks before and after testing.
Why test fuel pressure
Fuel pressure affects engine operation directly.
A pressure problem can cause symptoms that look like sensor, ignition, ECM, or vacuum problems.
Testing pressure helps separate an actual fuel-delivery problem from other possible causes.
Related trouble codes
Fuel-pressure problems may contribute to:
Fuel pressure can also be relevant to:
Low fuel pressure
Low fuel pressure can cause the engine to receive too little fuel.
Possible causes include:
- Weak fuel pump
- Restricted fuel filter
- Faulty fuel pressure regulator
- Low voltage at the fuel pump
- Poor fuel pump ground
- Restricted fuel line
- Leaking fuel line
- Incorrect fuel pump
- Wiring or relay problem
Possible symptoms include:
- Hard starting
- Long crank time
- No-start condition
- Hesitation
- Poor acceleration
- Lean running
- Code 44
- Stalling
- Poor performance under load
High fuel pressure
High fuel pressure can cause the engine to receive too much fuel.
Possible causes include:
- Faulty fuel pressure regulator
- Restricted return line
- Incorrect fuel pump
- Fuel-system modification problem
- Vacuum problem at the regulator on systems that use vacuum reference
Possible symptoms include:
- Rich running
- Poor fuel economy
- Black exhaust smoke
- Fuel smell
- Fouled spark plugs
- Rough idle
- Code 45
Pressure leak-down
After the fuel pump stops, fuel pressure should not immediately disappear.
A rapid pressure drop may indicate:
- Leaking injector
- Faulty fuel pressure regulator
- Fuel pump check-valve problem
- External fuel leak
- Internal fuel-system leak
Leak-down testing can be useful when diagnosing hard starting after sitting, fuel smell, rich running, or loss of pressure.
Diagnosis
Basic diagnostic checks include:
- Check for stored diagnostic trouble codes.
- Confirm the symptom.
- Attach a suitable fuel pressure gauge using the correct procedure.
- Check key-on fuel pressure if applicable.
- Check running fuel pressure if the engine runs.
- Check pressure during throttle changes or load if appropriate.
- Check whether pressure holds after the pump stops.
- Inspect for external leaks.
- Check fuel filter condition.
- Check fuel pump relay, wiring, voltage, and ground if pressure is low.
- Check the fuel pressure regulator and return system if pressure is high.
Relationship to Code 44
Code 44 indicates a lean exhaust condition.
Low fuel pressure, restricted fuel delivery, or a weak pump can cause an actual lean condition.
However, Code 44 can also be caused by vacuum leaks, exhaust leaks, oxygen sensor problems, wiring faults, or other sensor issues.
Fuel pressure testing helps determine whether fuel delivery is part of the problem.
Relationship to Code 45
Code 45 indicates a rich exhaust condition.
Excessive fuel pressure, a leaking injector, or a faulty fuel pressure regulator can cause an actual rich condition.
However, Code 45 can also be caused by oxygen sensor problems, MAP sensor problems, coolant temperature sensor problems, wiring faults, or other issues.
Fuel pressure testing helps determine whether the engine is being over-fueled.
Fuel pump relationship
A weak fuel pump may still make noise and may still move fuel, but may not produce enough pressure or volume under load.
Related topics:
Fuel pressure regulator relationship
The fuel pressure regulator controls fuel pressure and returns excess fuel to the tank on systems that use a return line.
A regulator problem can cause pressure that is too high, too low, unstable, or unable to hold after shutdown.
Related topic:
Notes
Do not guess at fuel pressure based only on pump noise.
A fuel pump can run and still fail to produce correct pressure. Likewise, a rich or lean trouble code does not automatically prove a fuel pump or regulator problem.
Fuel pressure should be measured with the correct gauge and interpreted using the correct service information for the engine and year.