OVERVIEW: The fuel supply volume and pressure to the fuel injectors are one of the most critical components supporting the engines’ ability to make peak power and sustain it, when requested by the driver. A compromised fuel system not only endangers the longevity of the engine but also dramatically increases diagnostic times as it is often overlooked.
Often components such as fuel pumps (high pressure and low pressure) can wear over time and use. This may lead to diminished fuel volume / pressure flow but may not hit the lower tolerances to cause fault codes, limp mode events or noticeable performance drops. When adding an engine power enhancement, the demand and expectation on the fuel system to perform to specification is greater at the higher power level. During the process of installing and testing a power enhancement, fuel system faults may come to the surface and need addressing. Depending upon the engine traits/history, fuel components may need to be replaced.
On conventional injection (port) which runs are 3-5 bar, there is often a single, in-tank fuel pump and over time and aggressive use, the fuel pump can lose its responsiveness to spool and achieve target rpm resulting in reduced output rates. This may not be something the driver will detect based upon the vehicle’s performance abut may be detected by data logging the output pressure and duty cycle (request and target values). In sufficient fuel delivery from the fuel pump with result in poor combustion fuel mixture, ratios, and higher temperatures.
Monitoring the fuel pumps performance is a good place to begin when trouble shooting and potentially replacing. We do not recommend using a different pump as that may change its flow rate.
Fuel pump control module
Modern vehicles manage their pump with control module. Often as a pump may wear and go undetected, the control module will be trying to compensate. A compensating control module will experience higher load and heat up and can, itself begin to drop in performance. As such we recommend replacing both the pump and control module at the same time, subject to their age/condition.
The fuel pump control module is software based and may be an outdated version. This could become incompatible if the ECU software has been updated exclusively. Hardware / software version history may also require verification, and the control module replaced with the newest version/updated at the OEM dealer.
Symptoms: Misfires at idle and/or full throttle. Erratic idle and fuel trims. Drop in power at full throttle. Insufficient fuel pressure faults. High exhaust gas temperatures.
Potential causes: Partially obstructed or dripping fuel injectors. Both port and direct injection fuel injectors have been found to experience blockage. Age and mileage has not been found to be major influence as we have tested 5.2L V10s as low as 2 years old with just 5K miles. Independent tests have shown us injectors suffer from obstruction causing dripping at idle to 60-70% compromised flow rates.
Consequences: Dripping injectors/obstructed injectors will cause poor combustion patterns/quality due to improper fuel atomization. Misfires are common but not a key consequence.
Obstructed/clogged fuel injectors inhibit the flow of fuel which poses a major engine safety issue as it could cause lean combustion resulting in increased combustion temperatures and damage the spark plugs, valves, and pistons over time/ under spirited driving / high speed runs.
Injectors with compromised flow will lead to the ECU trying to compensate by increasing fuel pressure and this may result in placing more demand on the fuel pump than it can supply. This can lead to erratic fault codes and limp mode events.
Action: Some manufacturers recommend the use of injector cleaning additives in the fuel system at major service intervals, but this will not solve the potential issue while adding an engine power enhancement.
Fuel pressure sensors: The fuel pressure sensor on FSI engines provides a critical input value to the ECU for performing numerous calculations. It is not uncommon for it to output intermittent or implausible values. This could be a result of contamination, or consequence of work performed on other parts of the fuel system. It may cause a DTC and should be replaced immediately.
Fuel Filter: Fuel filtration is an important factor for the fuel system and often goes overlooked. Some modern cars have filters inside the fuel tank itself and may not be replaceable. The filter will usually have a date stamp and should be replaced at major service intervals.
The in-tank fuel pump will have a mesh filter sock fitted to its inlet and this can become contaminated with debris in the fuel. The sock can be cleaned out with parts cleaner or replaced.