How to Get the Most out of Any Self-Tuning EFI

Words And Photos: Jeff Smith

Dale Carnegie in his best-selling book How to Win Friends & Influence People gives tips for getting past your fear of new people, as well as for how to make others feel comfortable interacting with you. Fuel system manufacturers seem to have put those tips to work, as the new crop of self-learning EFI systems are far from intimidating. The sales pitch is always the same: “Bolt it on and go! Your engine will be happily tuned without your help, and your life will be serene for the remainder of your days.” Well, all that is attainable – but you will have to put a little more effort into it than just bolting on the parts and calling it a day.

We’re going to use FAST’s EZ-EFI 2.0 system for this discussion, but most of these ideas will work for any of the available throttle-body, self-learning EFI systems, such as the MSD Atomic, Edelbrock’s E-Street, FiTECH, Holley’s Terminator, Quick Fuel’s QFI, and others. All of these systems are based on a 4150 Holley carb flange throttle body, equipped with injectors, that bolts in place of a carburetor and uses adaptive learning to quickly tune around your engine’s requirements.

In most cases, you can bolt on the throttle body, hook up the sensors, plumb the fuel system, carefully follow the manufacturer’s installation procedure, and the engine will start and run. We’re not going to replicate that here because it’s been done already in multiple magazine stories. What those other stories don’t tell you is how to get the most out of your system after it’s installed. That’s what we will be about. We don’t promise to solve all the issues, but we will cover several of the most common situations, both from past experience and from a recent FAST EZ-EFI class lead by FAST’s David Page, that can lead to poor drivability. A few simple changes can make a huge difference in the way your engine runs.

Let’s start from the place where you’ve installed the system and the engine’s running. One of the most important tuning steps you can take is to ensure the signals the ECU receives are accurate and not confused by outside interference. All EFI systems operate by gathering information from sensors that the ECU uses to make fuel and spark decisions. These signals operate mainly on a 0- to 5-volt scale. These very low voltage readings can be easily disrupted by electronic noise from the ignition system – mainly the coil, the high-tension coil wire, and the two-wire leads used to trigger a CD system.

So, the first thing to do even if your system seems to be running fine is to put space between any EFI sensor leads and the wires to the ignition coil. That especially includes the orange and black wires leading from a typical MSD CD box to the coil. Unlike a points system where the positive wire to the coil may carry 6 to 12 volts, a CD pumps roughly 500 volts through the orange and black wires. With higher voltages comes more potential RF interference from these wires. This should make it obvious why it’s crucial you pay attention to routing these wires away from the EFI system sensors and ECU.

Of course, this includes ensuring that the main power lead and ground wires for the system are routed directly to the battery. The battery at this point becomes a large filter or capacitor that can accommodate electrical noise without affecting the ECU. Additional ground straps between the body, the engine, and the frame are also excellent ways to ensure the system operates at peak efficiency.

Let’s move on to an area where you can improve performance. Cold start issues are often an area of concern. The EZ-EFI 2.0 offers ways to adjust the amount of fuel delivered when the engine is cold. You can find this adjustment in the Advanced menu under Enrichment Fuel, then find the Cold Start heading. If you think the air-fuel ratio is too rich with a cold engine, moving the adjustment with the minus button will remove some fuel. Be aware that the entire range is -8 to +8. Obviously, you can only test this when the engine is cold, so several sessions may be required to dial it in. This is important because excessive fuel on startup can wash oil from the cylinder walls, causing excessive cylinder bore and ring wear.

Cranking fuel is another area where tuning makes the whole starting process better. This is the amount of fuel delivered while the engine is cranking. If the engine has difficulty starting, before making adjustments take a moment to test the cranking voltage at the pink “switched 12v” wire in the harness. If cranking voltage is lower than 10 volts, the system may not trigger ignition. Lower signal voltage could also affect how well the engine starts.

Poor battery cables with high resistance are a common cause of starting issues. If there is more than a one-volt drop during cranking in either cable, they should be replaced with high quality, multi-strand 1/0 welding cables. Tuning to make starting crisper is a great way to improve the whole EFI experience. This can often be done just by increasing or decreasing the amount of fuel delivered. With the engine at normal operating temperature, the correct tune is the minimum amount of fuel required to start the engine. Also consider the ignition timing as part of this tuning process.

While enthusiasts place a majority of their attention at WOT power, a street engine spends 95 percent of its time at idle or part throttle. This puts a bounty on attaining the most efficient idle quality possible. Most installers drop the throttle body in place and assume the idle is set properly. But in some cases, including large displacement engines or those with lower idle vacuum, you may discover the engine sometimes stalls when the throttle is closed quickly on deceleration. The Idle Air Control (IAC) is a stepper motor that controls the amount of air by-passed around the throttle blades to maintain the commanded idle speed.

For the EZ-EFI 2.0, there is an IAC Calibration screen that displays a target box for the IAC position. If the engine stumbles or dies on rapid decel, you may have to manually open the throttle blades slightly. This will push the position of the IAC toward the left side of the target box. This gives the IAC more range of motion to overcome that stumble. If this is necessary, you will need to return to the initial setup to reconfigure the TPS so that fully closed is indicated by zero (0) on the TPS percentage scale.

Perhaps one of the most common issues that can occur with a self-learning EFI system is when after a period of operation of perhaps a dozen cycles of start-ups and shut downs, the engine begins to run rough, and it’s obvious the air-fuel ratio is very rich. This is often accompanied by the observed air-fuel ratio reported as consistently lean. The usual suspect in this situation is an exhaust leak. All adaptive learning EFI systems use the oxygen sensor as the main feedback loop. These sensors are aptly named because while their feedback is displayed in air-fuel ratio, this calculation is based on the amount of free oxygen in the exhaust system.

Essentially, the oxygen sensor uses the level of free oxygen in the exhaust as the indicator for air-fuel ratio. So if the engine is suffering from an exhaust leak somewhere (not limited to upstream of the oxygen sensor), the sensor reads that free oxygen as an indication the engine is running lean compared to the target air-fuel ratio. The ECU will always add fuel based on this feedback. Then, when the engine is shut down, the ECU adds more fuel based on the amount of correction required while the engine was running. Unfortunately, upon startup, the exhaust is still leaking, the oxygen sensor again senses excess air as the engine running too lean, and the ECU commands yet more fuel. The cycle repeats itself until the operator notices the engine is running obscenely rich.

Reconfiguring the ECU will reduce the amount of fuel, but unless the exhaust leak is repaired, the problem will quickly reoccur. The most common leak areas are the header gasket at the exhaust ports and the three-bolt collector flange gasket. If you find black, sooty marks outside the gasket’s sealing surface, that’s a likely leak path. Sometimes you may have to inject smoke into the exhaust system to find the leak. In obscure cases, the leak will only occur once the exhaust has achieved full temperature.

At this point, we’ve also exhausted our allotted space for this tuning story, and we have lots more information to share on how to take full advantage of the self-learning EFI timing controls. We’ll start on that story real soon, so check in with us to see what other little tricks you can apply to help your self-learning system become a bit more throttle friendly.

Parts List

Sources

Edelbrock
edelbrock.com

FiTech Fuel Injection
fitechefi.com

Fuel Air Spark Technology (FAST)
fuelairspark.com

Holley Performance Products
holley.com

MSD
msdignition.com