Figure 1 – Detonation notice top of piston
Figure 2– Notice crack at the ring land
Figure 3 — Heat buildup on underside of piston due to detonation
Figure 4 — Oxygen sensor
Figure 5 – TPS and manifold
Figure 6 — Fuel pumpsBy Dave Worden
In the three previous articles in this series on electronic fuel-injection (EFI) and digital fuel-injection engines, we discussed theory, basic components, and some troubleshooting scenarios. I hope by now things appear easier to understand, and all of the mystery has been removed. The reason for that statement is that with the emissions standards and the fuel changes, EFI/DFI is the future of gasoline engines and not just large horsepower.
As previously stated, Kawasaki, Briggs & Stratton, and Kohler Engines appeared to be the players that were working on and using electronic fuel injection. Both Kawasaki and Briggs & Stratton used a series of Manifold Absolute Pressure (MAP) sensors (1). Kohler uses both MAP sensors but then adds a closed-loop system (2). This means that Kohler engines try and “learn” the environment they are running in and will try to reach the ideal mixture. By taking readings from the exhaust, it then sends the information back to the engine control unit (ECU), and then based on load, speed, altitude, etc., it will try to make corrections and the necessary adjustments to try and achieve the “ideal” burn and most efficient use of fuel. Another term for this is an adaptive memory. This does lead to a cleaner- burning engine and less oil dilution and less carbon fouled plugs and less potential downtime. All of this saves money and keeps the professional cutters more profitable and the homeowner with a more reliable piece of equipment.
With all of this being said, it does make a technician wonder what else we will see. Or, is this a flash in the pan? (Remember, CDI Ignition and non-adjustable carburetors?) With the CARB and EPA emissions standards as they currently stand, the evolution of EFI is here to stay and grow. Polaris uses an EFI system on its equipment; Exmark, Scag, Walker, MTD and others manufacturers offer a variation in EFI/DFI.
Another variation that Kohler will introduce soon is engines with newer sensors. The addition of a MAP sensor located near the #2 cylinder of the intake manifold will detect not only Manifold Absolute Pressure but also timing when the #2 intake valve opens. The ECU would then interpret the information along with the speed sensor to calculate both Top Dead Center (TDC) and the correct stroke! This allows the engine to operate sequential injection. You will see an air inlet temperature sensor, which when the engine is at low speeds, air in the manifold has time to heat up before entering the combustion chamber. The warmer air has a greater tendency to cause detonation (see Figures 1-3) than cooler air. The ECU will receive the information from this sensor and adjust the ignition timing accordingly. If all this is not enough, there is an upgraded four-wire lambda (O2) sensor with a dedicated ground wire and a separate heater ground. This will allow the sensor to operate within about 10 seconds of start-up, and this is something necessary to achieve closed-loop operation. There are other conditions that must be met for closed-loop operation; this will just be an upgrade over the earlier system. Now all we need is a place to keep our favorite beverage cold!
As you have read what the engine manufacturers have done to date and what is planned for the future, the better knowledge you have of an EFI/DFI system, the easier your job as a repair technician will be.
I would like to share some additional notes and/or comments regarding EFI/DFI engines:
DFI (Digital Fuel Injection)
Do not disconnect the battery leads or any other electrical connections when the key switch is on, or while the engine is running, to prevent damage to the ECU.
When working on the engine and the electrical system, disconnect both the positive and negative leads from the battery to prevent any peak voltage surge to potentially damage the ECU.
Do not run ignition wire too close to the DFI wires. There is a possibility to have external electrical noise interfere with the system.
Avoid pressure washing near the wires and harness connection.
Do not operate the fuel pump dry.
Always inspect for air leaks in the system!
When testing the injectors, make sure you use the proper tester or make sure there is a bulb in the system to act as a limiter; it will protect the solenoid in the injector!
Whenever you are working with a system you are unfamiliar with, make sure you use the service manuals or service bulletins that are available from the manufacturer. They list the proper tools and show additional options to test and troubleshoot their systems.
EFI (Electronic Fuel Injection)
Disconnecting the battery for a minute or more will clear any fault codes in the system and the engine will go back to its pre-programmed settings until it is started and begins to re-learn its environment.
Figure 7 — ECUsWhen performing voltage or continuity tests, avoid spreading the connections.
With the single-wire Oxygen (O2) sensor in or around 700 hours, if the unit has had some service to it, the sensor may become lazy and it would be a good idea to replace it (see Figure 4).
With the EFI system on Kohler, if the throttle position sensor (TPS) is removed or moved for service (3), it must be initialized in order to run properly. This procedure is listed in the service manual and is easy to follow (see Figures 5 & 7) (3).
Do not operate the fuel pump dry (see Figure 6).
Avoid pressure washing near the wires and harness connection.
Do not run ignition wire to close to the EFI wires. There is a possibility to have external electrical noise interfere with the system.
(1) MAPs: Predetermined values or settings programmed into the ECU. They tell the ECU what ignition and injector settings are required for a specific set of conditions.
(2) Requirements for closed-loop operation: The oil temperature is greater than 86 degrees F (30 degrees C). Oxygen sensor warmed to minimum of 709 degrees F (376 degrees C). Engine operation in steady state (not starting, warming up or accelerating).
(3) There are two methods used: Manual Initialization used on MA 1.7 (35-pin metal ECU) and MSE 1.0 (24-pin plastic ECU). Auto Learn Initialization used on MSE 1.1 (32-pin plastic ECU).
Dave Worden has 40 years of extensive experience in the outdoor power equipment industry at the dealer, distributor and manufacturer levels. After beginning his career as a service technician for a dealership, he made the jump to a Central Distributor. There, he continued to work in the service department before he was promoted to educational director, representing Briggs & Stratton, Kohler, MTD and Tecumseh. He then moved up to the manufacturer level, serving as a territory manager for McCulloch Corp., a training specialist for Kohler Co. Engine Division, and a general manager for a manufacturer-owned dealership. In addition to being a contributing writer for OPE, Worden is currently operating a dealer consulting company called DJW Consultants, as well as serving as vice president of the Equipment & Engine Training Council, a committee chair for National SkillsUSA and an at-large representative for SkillsUSA Massachusetts.