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,” he 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,” explains Macy. “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,” says Macy.
So, let’s review those components before addressing more specific tuning steps. And we’ll also take a look at the latest trend of self-tuning EFI systems.
Wideband Oxygen Sensor: Macy promises that without this sensor it will be very difficult to get a car tuned correctly. It is the single most important sensor for any tuner; however, it must be free of distractions. Exhaust leaks, single-slip collectors that suck air through connection, and positioning it too close to the end of a collector on an open header may send the O2 sensor false information, thus prompting the ECU to add fuel the cylinders do not need.
“Most drag cars that run open headers have an issue getting a good O2 reading until close to 5,000 rpm,” says Macy. “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,” adds Macy. “Listen to how the engine runs and get it to run smooth.”
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. It’s most often positioned just before the throttle body or in the intake manifold. This sensor can also provide information for the ECU to add more fuel under cold conditions and less fuel when the air is hotter, so the engine runs a consistent air-fuel ratio, no matter the air temperature.
“I often see a lot of drag racers who remove this sensor thinking it’s not needed,” says Macy. “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 a signal it can decode as RPM.
“This signal is the number one issue most people have when installing a system,” cautions Macy. “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 RPM is greater than it actually is. If the ECU sees a false RPM trigger it will look up what fuel it needs, at say at 10,000 rpm, and flood the engine.”
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, such as 1-bar for naturally aspirated engines with no power adder or nitrous. Also available are 2-bar sensors for up to 14.7 psig (pounds per square inch gauge, meaning above the ambient air pressure) of boost and 3-bar sensors for up to 29.4 psig of boost. There are also common MAP sensors available up to 7-bar, or 88.2 psig.
Coolant Temperature Sensor: The coolant temperature sensor feeds back 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,” suggests Macy. “Every combo likes a different amount of timing. Just because you have run a big-block Chevy before does not mean all big-block Chevys like 32 degrees of timing. The fuel type and specific gravity plays a huge role in how the fuel burns and what timing the engine wants.”
Things that didn’t matter with your old carb are more of a big deal with EFI. – Brian Macy
“This method is called MBT, or maximum brake torque,” explains Macy. “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. 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.
First topic is the difference between open-loop and closed-loop fuel strategies. Open loop is where the ECU monitors the actual air-fuel ratio and notes how far it is off target, but it doesn’t use that information to make any real-time adjustments. In other words, the fuel map is programmed, and that’s what the engine gets. There are some conditions in which the tuner wants a specified fuel delivery, so the O2 sensor is basically taken out of the loop. Nitrous engines often run open-loop programs if equipped with EFI.
With a closed-loop system, the ECU checks the air-fuel ratio against the target numbers, but now the computer uses that information to adjust the fuel delivery to meet the target air-fuel ratio. The tuner also has the option of adjusting the correction factor and also switching between open- or closed-loop.
A dyno isn’t a necessity when adjusting the air-fuel ratio; however, it will speed up the process by hours, if not days. What’s needed are a properly calibrated air-fuel meter and a sealed exhaust system 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,” says Macy. “It’s always easier to remove fuel to make an engine run well than add fuel to a lean engine.”
No Need To Add More Fuel
Just like finding the peak torque with timing, the tuner will find that when the engine is happy, adding more or less fuel after that point doesn’t make more power.
“Now you have to decide what type of racing you’re doing and what mixture is needed,” says Macy. “An endurance engine will require a richer mixture than a drag race application where you will be at WOT for a short time.”
Often overlooked is that the ECU will change the amount of fuel based on the target A/F table no matter if running in open or closed loop. That’s because most ECUs operate with speed density calculations, which is basically estimating the expected airflow into the engine based on temperature, engine speed, manifold pressure and other factors.
“So, let’s say I tuned this engine to a 12:1 air fuel ratio and I now changed my mind and I want to see if it likes a 13:1 air-fuel ratio,” says Macy. “I would simply change the target ratio number and the ECU would recalculate the required amount needed in pulse width to get there.”
Macy offers this guideline of A/F ratios that will help provide a baseline for specific applications:
- Idle 13-14.7
- Light throttle cruise 13-15
- WOT w/no boost 12-13.5
- Low boost (1-10 psi) 11.8-12.5
- Med boost (10-20 psi) 11.4-12.0
- Hi boost (20-30+ psi) 10.8-11.4
In recent years, the EFI industry has developed self-tuning systems. The vehicle owner inputs the engine and vehicle parameters, the ECU takes over and maps out a program for a safe start-up, then monitors the driving style to make necessary changes to improve performance. But performance in this market also includes fuel economy and drivability.
“Things that didn’t matter with your old carb are more of a big deal with EFI,” says Macy.
Understanding Self-Learning EFI
What is self-learning? Well, the ECU has a target air-fuel ratio that the owner sets in the program. With most self learning ECU’s you will only get three target air-fuel ratio boxes to fill in: one for idle, one for cruise and one for WOT. The ECU will then drive around in closed loop, making adjustments via the O2 sensor to meet those targets.
“It also looks at how much the O2 sensor is correcting to get to target,” says Macy. “If the corrections are high enough and for a long period of time, it will apply those corrections to the main fuel table.”
The ECU then compares the fuel table with the target air-fuel ratio and corrects again. Once the learning is complete, the closed loop corrections will be at a minimum.
“This is the same process that a tuner will do with your fuel table while tuning,” reminds Macy.
There are limitations to the self-learning systems, however.
“I have had several customers who tried to use a self-learning system only to find out that their dual-quad, big rowdy cam engine with short exhaust didn’t learn very well. Self-learning systems are really geared toward engines making 10 inches of vacuum or more,” says Macy. “If your combo does not make this much vacuum, then you should be looking at one of the laptop programmable ECUs that may also have self-learning capabilities built into them. I have also had some issues with engines that had a stock cam and really made too much vacuum.”
That could be a problem because the drive and deceleration portions of the map were the same squares. The ECU would take fuel away when the throttle was chopped back, but then the engine would be lean when the driver got back on the throttle.
“In this case, we used a laptop and stand-alone system and had the car fixed in hours, compared to weeks making the self-learning ECU work,” says Macy. “Not every combo will respond well with the self-learning’s one size fits all strategy. With the laptop programmable systems you can actually use the learning if you wish, but put some restraints into where it learns and how much. I’ve found that most competent tuners can tune the car much faster and do a better job than the self-learning can do.”
Finally, Macy offers some general advice for setting up any EFI system. First, keep the wiring clean and follow the instructions.
“Some of the questions I get are so basic that they’re covered on page one of the instructions,” sighs Macy. “When the instructions say go directly to the battery, this means wire directly to the battery, not the safety shut off switch or anywhere else. The ECU will still shut off when the ignition circuit is removed. So don’t worry, the tech guy can still kill the car with the kill switch.”
Lesson for the Day
- Use all the sensors
- Use an engine or chassis dyno to find MBT and set the ignition timing
- Different applications require different air-fuel ratios
- Self-learning EFI systems take a conservative approach to tuning
- Read the manufacturer’s instructions and make sure the system is wired properly
“Depending on the system, there may be more than one input for the RPM connection,” says Macy. “Again, read the directions and make sure that you connect this properly. Go by the EFI instructions and not the manufacturer of the distributor or crank trigger. Sometimes the polarity is switched for a reason.”
When going to EFI, lock out the distributor. Let the EFI system control timing. The car will idle better and allow more precise timing adjustments. Also, most systems have fuel pump and fan control by triggering the ground on their relay. It’s very easy to connect and will turn on the pump for prime and fan on/off at the correct temperature.
“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.”