Fiesta ST - Fuel System Weakpoints
- on April 03, 2020
- Categories: Tech Articles
Now that we have a better understanding of the Fiesta ST fuel system, we can dig a little deeper into it's common weak areas. The OEM fuel system can reliably fuel the 1.6L Ecoboost engine to ~300whp, depending on modifications and altitude. Beyond that, the OEM hardware becomes a limitation and parts must be added or upgraded to help provide the added fuel needed for higher power levels.
There are (3) known weak areas of the OEM fuel system, and we will discuss each particular area (in order of occurrence), and what you can do to correct the issue. We will also discuss how you can spot possible fueling issues or wearing components, before they get worse and possible engine damage occurs.
Problem #1 - Fuel Injectors (roughly 260whp)
The first component to show a lack of flow is the fuel injectors. Once boost is raised above ~23 psi (at 6,000 RPM and up), proper AFR can no longer be maintained. You will actually see AFR start trending leaner and leaner as RPM's increase. Lowering boost in the upper RPM can help counteract this, but in turn reduces power, going against the reason you replaced the turbo to begin with! Take a look at the graph below, and you can see the AFR trending lean from 6,000 RPM on.
After the addition of an Auxiliary Fuel Kit, proper AFR can be achieved. Both Single Port or 4 Port Aux Fuel Kits will accomplish this, but the 4 Port Kit is recommended for power levels higher than 375whp. Another solution to this issue would be aftermarket Bosch injectors rated for 30% more flow. I will be testing these injectors over the next few weeks and release more information when it is available.
Problem #2 - HPFP (roughly 300 ft/lbs)
The next component to show signs of weakness is the HPFP. This pressure can be monitored on the AccessPort as "FRP Actual". Typically, you should always see pressures over 2,000 psi at WOT. As boost is increased, torque also increases respectively (to a point). You can monitor a torque reference from the AccessPort as "Load Actual". It has been discovered that at roughly 2.5 Load Actual, fuel pressure begins to dip. It then usually regains proper pressure as torque/load is reduced after spool up. Take a look at the graph below and you can see HPFP pressure dipping at peak torque/load.
With the same Aux Fuel Kit used to address our fuel injector issue, our HPFP issue can also be addressed. Fuel can be added in this region of the RPM band, and proper pressure is regained. Both Single Port or 4 Port Aux Fuel Kits will accomplish this, but the 4 Port Kit is recommended for power levels higher than 375whp.
Problem #3 (roughly 360whp)
The last component to cause issues is the in-tank fuel pump. The pressure from the tank can be monitored as "Lowside FP", and should always be near 90-100 psi on a Dizzy Tuning (larger turbo) custom tune. As you see in the graph below, fuel pressure begins to drop as the RPM's increase toward redline. It simply just cannot provide the amount of fuel needed at this power level. This appears to most commonly happen around 360whp and/or 30+ lb/min of airflow.
A solution to this would be an aftermarket in-tank fuel pump assembly, similar to the Bravo Alpha. This is another item I plan to add to the Dizzy Tuning Fiesta ST for further testing. So keep a eye out for data on that, as well as the aftermarket injectors!