Have you ever seen engines with custom-colored AN fittings at the ends of braided lines and wondered how they came to be? This isn't a critical tech element, but it's interesting nonetheless. Dunking fittings in a plastic container of household oven cleaner will strip away the anodize finish and leave them ready for new, custom color-anodizing.
Fuel Pumps And Regulators
Fuel pumps send low- or high-pressure (EFI) gasoline feeds from the tank through lines and up to the engine. They maintain enough pressure to keep the fuel from boiling.
The fuel-injected engines in stock and street/strip 'Stangs are usually fed by in-tank electric pumps. 'Stangs with considerable amounts of power and torque use high-pressure electric fuel pumps such as Aeromotive's A1000 or Eliminator to get an engine's fire fueled. Big pumps such as these are efficient and capable of continuous-duty operation on the street.
An interesting note on fuel pressure that may come as a surprise to many of you; fuel pressure is actually at its highest when the engine is at idle and lowest when an engine is running at top speed. It's also worth noting that higher pressure results in reduced flow, so the more base pressure you run, the harder your pump has to work. Flow rate is critical for high-rpm and boosted applications, as high rpm reduces time to get fuel into the cylinders and high boost pressure actually pushes back against the fuel.
In order to maintain fuel-pressure consistency, a bypass regulator must be used to control the amount of fuel pressure in the lines. In boosted applications, regulators draw a vacuum signal from the intake manifold to increase fuel pressure as vacuum decreases and rpm increases during acceleration.
As you would expect, performance can be enhanced or hindered by fuel-pressure changes that are made through what seem to be simple turns on a regulator. We found this interesting and informative rundown of do's and don'ts for tuning EFI engines with fuel pressure on Aeromotive's Web site. We recommend you use them when dialing in the new fuel system in your 'Stang.
1) Install a fuel pressure gauge before removing the stock fuel pressure regu-lator. Leave it installed until the final adjustments are made to the new one.
2) Don't use liquid-filled fuel pressure gauges on any automotive tuning application. By design, they can't provide consistent readings as the gauge temperature changes.
3) Begin by setting your adjustable regulator to the same fuel pressure as the stock one. Remember: Always remove the vacuum/boost line when checking or adjusting the base fuel pressure. Don't forget to reconnect it before driving.
4) Initial changes in fuel pressure for performance tuning should always begin with adjustments toward a higher pressure than stock. This helps find where the engine wants to be regarding fuel while avoiding an engine-damaging lean condition in the beginning stages of tuning.
5) Make small, incremental changes and measure the results after each change. Tuning on a chassis dyno or at the track makes any affect on performance easy and safe to observe and evaluate.
6) Stop adjusting the pressure once noticeable improvements stop, especially if you're gaining horsepower by going to lower pressure (leaner) settings. For engine durability, it's recommended that the final fuel pressure setting be 1-2 psi above the pressure that produced the best lean power.
7) The objective of changing fuel pressure is to optimize the engine's air/fuel ratio for best wide-open-throttle (WOT) power. Tuning with the aid of a wide-band air/fuel meter is strongly advised.
8) Adjusting the base fuel pressure of most modern EFI engines will initially affect the WOT and idle/cruise air/fuel. The permanent effects are mainly to full-throttle air/fuel only. Make fuel-pressure changes based on the ratio at WOT, and ignore driveability/cruise air/fuel until WOT is correct and safe.
9) During low-load cruising, most PCMs run in closed loop, using the O2 sensors' feedback to constantly trim injector-pulse width toward the optimum, lean air/fuel ratio of 14.7:1. This 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's necessary to maintain stoich and stores this information until the learned memory is cleared by disconnecting the computer from the battery for at least five minutes.
10) Air/fuel numbers can be confusing. The ratio is represented as the number of parts air per one part gasoline. The bigger the first number, the more air is in the engine per part of fuel (lean). The smaller the first number, the less air per part of fuel (rich).
11) The best WOT air/fuel ratios vary with the engine combination. Naturally aspirated engines make their best power between 12.0:1 (richest) and 13.2:1 (leanest). Forced-induction combinations like to be richer than their naturally aspirated counterparts. They still should never be as lean as 12.5:1, but they can be as rich as 11.0:1 for high-boost efforts on pump gas. On the dyno, always begin with a rich air/fuel mixture and gradually go leaner while closely monitoring for detonation.
12) Changing fuel pressure with a stock computer to solve driveability problems may yield only temporary results. Adjust fuel pressure to achieve a desirable WOT air/fuel, then leave it alone.
13) Once fuel pressure is set to produce an optimum air/fuel ratio, unplug the PCM or disconnect the battery so it will clear its memory. Reconnect power after five minutes and drive the car for several days, allowing the computer enough time to learn a new strategy for best driveability and performance in closed loop. If driveability problems exist after several days, consider a custom chip or reprogramming of the stock processor to regain good closed-loop performance. If the best fuel pressure for driveability is different than optimum pressure for full-throttle performance, establish WOT fuel pressure, but note the best pressure for driveability. The information can be programmed into a custom chip or tune.
14) Remember, as fuel pressure is increased, the amount of fuel flow available from the pump decreases. This applies 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 ensure enough flow when the pressure is at its peak.