Words: Mike Magda, Story courtesy of Dragzine

The wide flexibility of adjustments that electronic fuel injection offers may overwhelm a novice engine tuner, so sometimes it’s a good idea to refocus on a few basic tasks that may help solve more pressing issues with the engine.

Brian Macy teaches tuning classes through EFI University and also runs Horsepower Connection, a fuel-injection specialty shop that works with a wide variety of engine projects and can also supply EFI systems through its online shop, the EFI Store.

“EFI isn’t as easy as your old carburetor counterpart,” Macy warns.

With that understanding out of the way, Macy says EFI is much more precise because the tuner is telling the injector when and how long to open, which in turn allows fuel under high pressure to spray into the intake manifold in precise amounts at the right time.

“This is called the pulse width,” Macy explains. “A carburetor, on the other hand, pulls fuel through the booster. As the engine sucks more air, in return more fuel gets pulled out of the booster into the engine.”

In addition to monitoring fuel delivery, modern EFI systems can also control the ignition timing through the electronic control unit (ECU), thereby giving the tuner complete authority over the engine’s critical functions to produce optimum horsepower. It’s a lot of power in the tuner’s hands, and the two biggest questions still facing tuners are how much fuel and when to fire the spark plugs. Again, it’s returning to basics.

“To fuel and tune the engine, we need six basic sensors,” Macy says.

Wideband Oxygen (O2) Sensor: This is the single most important sensor for any tuner. However, it must be free of distractions such as exhaust leaks, single-slip collectors that suck air through the connection. Also, positioning the sensor too close to the end of a collector on an open header may send the O2 sensor false information.

“Most drag cars that run open headers have an issue getting a good O2 reading until close to 5,000 rpm,” Macy says. “Everything before that will just be a guess at that point.”

Also, big cams with extreme overlap can confuse the O2 sensor. This sensor must be utilized with a strong dose of common sense. If the sensor shows lean but the plugs are black, then something isn’t quite right.

“Give the engine what it wants and not an air fuel ratio you think it needs,” Macy adds. “Listen to how the engine runs and get it to run smooth.”

Intake Air Temperature Sensor: This sensor is part of the base fuel calculation for most ECU’s and is responsible for reading the temperature of the incoming air into the intake.

“I often see a lot of drag racers who remove this sensor thinking it’s not needed,” Macy says. “If removed, the ECU will default to a low-temp value and add extra fuel.”

Throttle Position Sensor: This sensor is responsible for acceleration enrichment and informs the ECU when the engine is at idle or moving down the road or track.

Distributor or Crank Trigger: This sensor provides the ECU an rpm signal.
“This signal is the number one issue most people have when installing a system,” Macy cautions. “Care should be taken to make sure this wiring does not come near components like coils, spark plug wires, wires to the coil, alternator wiring, and the distributor cap. Any source of electrical interference may trick the ECU into thinking the engine is at a different rpm.”

MAP Sensor: Short for manifold absolute pressure, the MAP sensor in most systems will tell the ECU the load on the engine during light throttle, wide-open throttle (WOT), or boost. Once the ECU digests this manifold vacuum/pressure information, it can look up how much fuel, timing, and target air-fuel ratio is needed to run the engine. MAP sensors come in common sizes for normally aspirated engines as well as those running boost or nitrous.

Coolant Temperature Sensor: The coolant temperature sensor relays info to the ECU to determine how much fuel is needed during warm up and/or enrichment during acceleration.

Now that the hardware is in place, setting the ignition timing is perhaps the most challenging tuning operation for most people, even for carbureted vehicles.

“How do you find the correct timing? The only real 100-percent way to find the correct timing is to use a chassis or engine dyno,” Macy suggests. “A dyno allows the tuner to hold the engine at a steady load and change the timing to achieve peak torque. This method is called MBT, or maximum brake torque. “If we start at, say 3,000 rpm, and hold the engine there, we can start with a value of 10 degrees and slowly advance the timing until the torque no longer moves,” Macy continues. “This is the point of MBT. You will find that after moving the timing past MBT, the torque will plateau and no longer change. Since horsepower is a mathematical formula derived from torque, you will find that if you tune each point to the best torque you will also find the best horsepower. After tuning for MBT, you can go to the track and play around with some small timing changes to see if the engine will accelerate quicker.”

Getting The Fuel Right

Finding the optimum air-fuel ratio is a little less complicated thanks to the ingenuity of the wideband O2 sensor. A quality wideband O2 sensor will read air-fuel ratios from 9:1 up 22:1, giving the tuner much more information and flexibility than a narrow-band sensor that generally comes from the factory and reads only in the 13.5:1 to 15:1 range effectively.

A dyno isn’t a necessity when adjusting the air-fuel ratio, however, it will speed up the process by hours, if not days. A properly calibrated air-fuel meter and a sealed exhaust system are needed to ensure a quality sample of fumes will be analyzed.

“As I tune an engine for a racer or even a street car, we always start out on the rich end of the scale then get the mixture to come around where the engine is happy,” Macy says. “It’s always easier to remove fuel to make an engine run well than add fuel to a lean engine.”

“The coolest part of having an EFI street car, race car, or offshore boat is the data the system will provide you through the logging,” sums up Macy. “You will learn stuff you didn’t know about your combo and will be able to fine tune it to run at peak efficiency and horsepower.”

Sources

The EFI Store
theefistore.com

Dragzine
dragzine.com