Fueling The Beast

Today we are going to talk about a few things today concerning fueling. I’ll be highlighting fuel pumps, fuel injectors and when and why they should be replaced or upgraded.

Fuel Pumps

First and foremost fuel pumps. I have been seeing this issue more often as the earlier turbo Subaru cars are getting older and also when upgraded fuel pump are pushed to their limits. Most of the time the fuel pump just completely fails and leaves the user stranded wherever they are. Other times the pump starts to loose pressure and it may not even seem apparent while idling or cruising but will be seen when then engine load increases. As the stock O2 is an narrowband you will never know if you are going lean. A Wideband will help in this situation to alert user of lean condition. It is always reccomended that a stock fuel pump be changed when the car has significant mileage or going to be pushing much more power than stock.. Below are a few examples of cars that came in with failing fuel pumps.

 This is a Stage 2 2006 STI with stock fuel pump and you can see the AFRs go lean as the rpms rise. No amount of tuning could get the AFRs to come down. Cause is a failing pump.

This is a Stage 2 2006 STI with stock fuel pump and you can see the AFRs go lean as the rpms rise. No amount of tuning could get the AFRs to come down. Cause is a failing pump.

 This is the same 2006 STI as above. You can see the IDCs go well above 100%.... 

This is the same 2006 STI as above. You can see the IDCs go well above 100%.... 

 This is highly modified 2012 STI with forged motor, rotated turbo and plethora of supporting mods. As the tuning session proceeded the AFRs kept on going lean even though we were adding more fuel every run. On inspection of installed fuel pressure gauge it was confirmed that the fuel pressure was indeed dropping off... Cause = failing pump..

This is highly modified 2012 STI with forged motor, rotated turbo and plethora of supporting mods. As the tuning session proceeded the AFRs kept on going lean even though we were adding more fuel every run. On inspection of installed fuel pressure gauge it was confirmed that the fuel pressure was indeed dropping off... Cause = failing pump..

So before you come in for a Protune or replacing stock pump it is highly reccomended that the fuel pump be changed out to an aftermarket unit if it has more than 100,000 Kms or going to be going beyond stage 2. If you are to do more upgrades in the future it is easier to purchase and install fuel pump ahead of time. Its fairly inexpensive and easy to install. You can run an aftermarket fuel pump without any other modifications. Installing a fuel pump DOES NOT REQUIRE A TUNE.. Installing a fuel pump does not gives you more fuel as in make you run rich. It only allows additional fuel to be supplied if you were to run more boost or to run a bigger turbo and require more fuel. The stock Raising Rate Fuel Pressure Regulator maintains the fuel pressure at 43.5 psi (+ manifold pressure) no matter how much fuel may be available from the fuel pump. As for options for fuel pumps, Walbro, DeatschWerks and AEM have been proven pumps.

Fuel Injectors

The next thing we going to look at are fuel injectors. Usually stock fuel injectors are sufficient enough for Stage 2 levels. But even at stage 2 levels the injectors are pushed to their maximum limit. Injector Duty Cycle (IDC) is the time that an injector is open and spraying fuel. The rule of thumb is you want to keep IDCs within 80-90%, that way there is some headroom. Below is a section of 2 logs, one from WRX and one from an STI both showing Injector Duty cycles in the 95%+ range at stage 2 power levels.

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Therefore when selecting injectors you want to make sure your IDCs of said injectors fall within the range of 80-90%. For Stage 2 needs the stock injectors can be made to work well. When getting a Protune the fueling can be adjusted a bit to were they don’t go beyond 90-95% while still getting good power/torque gains.

The technology in new injectors has jumped leaps and bounds in the last few years. Before the options were either decapped or modified stock injectors. Now there are many affordable aftermarket injectors available that are manufactured specifically for performance tuned vehicles. Before getting a 1000cc injector to idle like a stock injector was unheard of. And now injectors as big as 2200cc can easily be tuned to idle and run like stock injectors. Recently I have been loving to use the new ID1050x Injectors. They can be used on a basic stage 2 car all the way up to full blown rotated setups. They drive and run just like stock. The newer DeatschWerks Injectors are good units as well. Injectors are another thing that can be upgraded before getting on to the path of major mods/turbo upgrade. Only thing is that Injectors DO REQUIRE A TUNE.. Cobb has recently released Off The Shelf (OTS) maps for its 1000cc (ID1050x) injectors. So as of now you can run bigger injectors with an OTS map :)  Please check Cobbs website and make sure the map is available for your car. For Opensource users we still have the option to Protune your car with bigger injectors.

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Other things in the fueling department like Fuel rails and Fuel Pressure Regulators will be discussed at a later time. We also will be touching on the subject of the infamous GR Stumble issue.

 

Thanks for reading…   

Amritpaul Bhullar