Advanced Tips for Changing Fuel Pressure on EFI Systems - Engine Builder Magazine

Advanced Tips for Changing Fuel Pressure on EFI Systems

Changing the fuel pressure on an EFI System is an effective method of affecting engine performance and making more power. However, there are many do’s and don’ts, and rules of thumb that can be frustrating to learn the hard way.

sidebarFAST air fuel meter
A wide-band sensor based digital air/fuel meter seen here is a very ­affordable tool that every engine tuner should have in their tool box.

Below are many small, but key points, tips and insights all engine tuners should to know and understand before cranking on that adjustable regulator.

1.) Install a fuel pressure gauge before removing the stock fuel pressure regulator and leave it installed until final adjustments are made to the new one.

2.) Do NOT use liquid-filled fuel pressure gauges on any automotive tuning application. By design, they cannot provide consistent readings as the gauge temperature changes.

3.) Begin by setting your adjustable regulator to the same fuel pressure as the stock regulator. Remember, always remove the vacuum/boost line from any regulator when checking or adjusting “base” fuel pressure, then, remember to reconnect it before driving!

4.) Initial changes in fuel pressure for performance tuning should always begin with adjustments towards a higher pressure than stock. This helps to find where the engine wants to be for fuel, while avoiding an engine damaging lean condition in the beginning stages of tuning.
EFI, performance, fuel, racing, fuel pressure
5.) Make small, incremental changes and measure the results after each change. Tuning on the wheel dyno or at the track makes any affect on performance easy and safe to observe and evaluate.

6.) Once noticeable improvements in performance STOP occurring, STOP ADJUSTING PRESSURE, especially if you’re gaining HP by going to lower pressure (leaner) settings. For engine durability, it is strongly recommended that the final fuel pressure setting be 1-2 psi above the pressure that produced lean best power.

7.) The objective of changing fuel pressure is to optimize air/fuel ratio (AFR) for best wide-open-throttle (WOT) power. Tuning with the aid of a wide-band O-2 A/F meter is strongly advised.

8.) Adjusting the base fuel pressure of most modern, EFI engines will initially affect both the WOT and idle/cruise AFR. However, the permanent affects are mainly to WOT AFR only. Make fuel pressure changes based on WOT AFR and ignore drivability/ cruise AFR until WOT is correct and safe!

9.) During low load cruise, most engine management computers run in “closed loop”, using the stock O2 feedback to constantly trim injector pulse width (fuel delivery) towards the lean best AFR of 14.7:1. This target A/F is commonly referred to as “stoich” or “stoichiometric” and is the chemically correct balance of air and fuel for a complete burn.
The computer “learns” what is necessary to maintain “stoich” and stores this information until the learned memory is cleared by disconnecting the computer from the battery for 5 minutes or more.

10.) AFR numbers can be confusing. The ratio is represented to be the number of parts air per one part gasoline. Thus the bigger the first number, the more air is in the engine per part of fuel (lean). The smaller the first number then, the less air per part of fuel (rich).

11.) With gasoline; A 10:1 AFR is VERY RICH. A 20:1 AFR is VERY LEAN. Best WOT AFR varies with the engine combination and the fuel used. Natural aspirated (NAS) engines burning gasoline will make best power between

12.0:1 richest and 13.2:1 leanest. Forced induction combinations like to be richer than a similar NAS engine. They should never be leaner than 12.5:1 and may go as rich as 11.0:1 for high-boost on pump gas. Always start with the richer AFR,then, gradually work leaner while closely monitoring power and looking carefully for signs of detonation.

12.) Changing fuel pressure to solve drivability problems, with a stock computer, may yield only temporary results. Adjust fuel pressure to achieve a desirable WOT A/F, then, leave it alone.

13.) For best drivability with a stock computer, once fuel pressure is set to produce the correct WOT A/F, unplug it to clear all learned memory, then plug it back in after 5 minutes and drive the car for several days, allowing the computer enough time to learn a new strategy for best drivability and performance in closed loop. If drivability problems still exist after several days, consider a custom chip or “flash” to the stock ECU to help regain good “closed loop” performance.

14.) If the best fuel pressure for drivability is different than for WOT performance, set the pressure for best WOT performance and note the best pressure for drivability so you can give this information to a chip burner or programmer. IF THE BEST PRESSURE FOR DRIVABILITY IS LOWER THAN THAT FOR WOT, DO NOT RUN WOT WHEN THE REGULATOR IS ADJUSTED FOR THE LOWER PRESSURE OR MAJOR DETONATION AND ENGINE DAMAGE CAN OCCUR!

15.) Remember, as fuel pressure is raised higher and higher, the flow available from the fuel pump gets smaller and smaller. This is particularly applicable to forced induction combinations with an FMU. If fuel pressure must be raised excessively, be certain you have more fuel system than you think you need in order to assure there is enough flow when the pressure is at it’s peak.

Source: Aeromotive

You May Also Like

Shop Solutions September 2023

Engine shop tips and tricks.

Engine Builder and Engine Pro present Shop Solutions in each issue of Engine Builder Magazine and at enginebuildermag.com to provide machine shop owners and engine technicians the opportunity to share their knowledge to benefit the entire industry and their own shops. Those who submit Shop Solutions that are published are awarded a prepaid $100 Visa gift card. Submit your Shop Solution at [email protected]. You must include your name, shop name, shop address and shop telephone number. Submitted Shop Solutions not published will be kept on file and reevaluated for each month’s new entries.

How to Properly Crate a Performance Engine for Shipping

PPLUS Global Logistics, a freight management provider, recently released a guide outlining the proper steps for crating a performance engine for shipping. Obviously, given the expense and potential for damage to these high-value engines, shipping them requires careful attention to detail to ensure their safe transportation. Related Articles – Shop Solutions August 2023 – The

Shop Solutions August 2023

Engine shop tips and tricks.

The Best of Both Worlds: Twin-Charged Engines

Not to be confused with twin-turbocharging, twin-charging is the innovative combination of a supercharger and a turbocharger. It’s nothing new – Lancia, Nissan and Volkswagen were among the first to use the combination back in the ‘80s, but it’s hardly common today.

Crank Balancing Update

If there’s anything all of us in this industry have come to understand, it’s that you can never be certain someone else did the job correctly – and when it comes to crankshafts and crank kits that you or a customer might purchase, it’s imperative to ensure a proper balance job was performed and not just trust that it was because it says so.

Other Posts

731 cid Outlaw 4.840 Bore Space Nitrous Engine

When it comes to building a 4.840″ bore space engine for drag racing, the class is limited on deck height and limited on bore space, but anything else pretty much goes. Pat Musi of Pat Musi Racing Engines recently finished development on his state-of-the-art 4.840 engine platform, and this 731 cid nitrous combo is freaking awesome!

Stanadyne Partners with Wesley Motorsports to Provide High-Performance GDI Fuel Pumps

Stanadyne is partnering with Wesley Motorsports to provide the American racing company with its high-performance gasoline direct injection (GDI) fuel pump technology. Wesley Motorsports will use Stanadyne’s 350-bar, high-flow GDI pumps on its custom-built T6 Hurricane HO engine being featured in its 2021 Dodge Challenger Mopar Drag Pak specialty vehicle.  Related Articles – ATI’s New OEM Style

Aviaid Series 2 Pump Line

With four available scavenge section widths, plus 4, 5 and 6-stage designs, Aviaid can tailor scavenging vacuum to an engine builder’s needs.

SRX Announces 2024 Racing Calendar

Officials with the Camping World Superstar Racing Experience (SRX) have announced the 2024 racing calendar, which will once again be highlighted on ESPN’s “Thursday Night Thunder.” Related Articles – PERA and Mahle Host Webinar on Low-Speed Pre-Ignition – Lucas Oil Products Teams Up With NXG Youth Motorsports – Spec MX-5 to Become SCCA Runoffs Class