Stand-Alone ECU for Fuel Efficiency
If you do an internet search for Stand-Alone ECUs, you will find products that support nitrous, boost, water injection, individual ignition coils, sequential fuel injection, electric fan, air conditioning, cruise control, automatic transmission control, variable valve timing, and other features. If you are considering a Stand-Alone ECU to improve fuel efficiency, your goals are probably quite a bit different than what is being promoted by the Stand-Alone ECU companies!
The manufacturers of Stand-Alone ECUs by the nature of EPA (and perhaps CARB) mandated laws focus on off-road racing performance. In the USA, you probably cannot simply replace your factory ECU with a Stand-Alone and still pass annual emission inspections. I have yet to read about a Stand-Alone ECU that provides OBD-II Data Stream and DTC (and other) information that satisfies state emissions inspection criteria.
Therefore your typical Stand-Alone ECU manufacturer will be targeting either an older (read this as emissions exempt antique) vehicle EFI retrofit, or later model race-only application. If you want to boost the efficiency of your daily driver, and it falls within the typical range of 5 to 25 years old (as of this writing, would be vehicles from 1998 to 2018), and are considering a Stand-Alone ECU, you will probably get into conflict with your state emission regulatory agencies come registration time. Diablo or HP Tuner (and others) may be a better compromise for you, as they are legal.
For most US states, the line drawn in the sand as far as emissions regulations is 1996. This is the model year where OBD-II was implemented. 1995 and older vehicles are typically only subjected to a visual inspection to ensure the catalytic converter, EVAP, EGR, and other emissions equipment are still in place. In most cases they don’t even verify the equipment is operational; only present. They may also test your fuel filler cap to ensure that it still seals properly.
OBD-I Stand-Alone ECU Considerations
If you are working with a 1995 model year or older vehicle, chances are you may legally install a Stand-Alone ECU for the street and reap the benefits of improved fuel efficiency. Perhaps the first question to ask yourself is, “Why would I need to replace my factory ECU with an aftermarket Stand-Alone?”
The first 2 answers would be better control of ignition timing when flame propagation rate has changed, and better AFR control using an after-market Wide-Band oxygen sensor (WBO2). If you talk to any seasoned dyno operator, he/she will tell you there is way more power (and efficiency) to be made with ignition timing control than precise fuel delivery control.
If you add an HHO system, you will need to retard ignition timing from factory settings. If you add an EGR or water injection system, you will need to advance it. If you add a complex network of HHO (on-board hydrogen generator), EGR/H2O, PDI (Plasma Discharge Ignition), and other enhancers, you really need to drive the vehicle, data log what’s going on, and tune accordingly. The more complex your hardware, the more valuable the data logging features of an after-market ECU become to you.
When implementing HHO, PDI, fuel heaters, and other enhancers, you can seriously boost fuel efficiency by targeting an AFR leaner than stoic (typically 14.7:1 for gasoline). Modern Direct Injection (GDI) engines may run as lean as 40:1 under certain operating conditions! The fact that the engine still runs — and still produces expected power — proves that leaner-than-stoic (>14.7:1) AFRs are not only possible, but practical; under the right conditions.
When you peruse the vast array of after-market ECU offerings, you will see the companies boast the number of auxiliary inputs and outputs (I/O’s), analog and digital, as well as Pulse-Width Modulated (PWM) outputs. These I/O’s can be used to control your HHO system, add-on EGR valve, or water injection system. The analog input can be tied to a turbo MAP sensor that reads vapor pressure in a fuel vaporizer. A digital output (perhaps PWM driven) can control a heating element for that vaporizer. In the old days, Super Carbs typically started on the stock carburetor and switched over when the vaporizer was operational. This usually meant the driver watched a gauge (like temperature) and manually switched a valve when the auxiliary system came online. This can now be performed with software automation.
Let’s look at aftermarket ECU features that can be purposed for efficiency gains:
Digital Inputs
Standard digital inputs typically include Key-On, Crank Position Sensor (CPS), Camshaft Position Sensor (CMS), brake pedal switch, cruise control buttons (1/0, Set, Resume), clutch pedal switch, AC high pressure switch (and other HVAC inputs); anything sensed that delivers a digital input signal to the central controller (1 or 0, ON or OFF, Yes or No).
You can mount a toggle switch under the dash that connects to one of the digital inputs on an aftermarket ECU. When “ON”, it can enable a function when conditions are right, such as HHO, water injection, ozone, EGR, or… If you have a fancy fuel vaporizer, you could mount a pressure switch that sends a high signal to a digital input when pressure exceeds your predetermined threshold. The nice thing about generic digital inputs is you can assign them to do whatever you want.
Digital Outputs
Digital outputs are often tied to ignition coils (ignition timing control), fuel injectors (Injector Pulse Width — IPW), coolant fan ON/OFF, Check Engine Light (CEL), transmission solenoids, Nitrous solenoids, or other racing features. Think about what you might control with an ON/OFF output. You could activate PDI, HHO (provided you have a system with it’s own controller), EGR, a light on the dash that tells you something is right or wrong, a simple fan control (ON or OFF), or many other possibilities. Some outputs are rated for low current (1 amp or so), while some may power upwards of 10 amps.
Analog Inputs
Analog inputs in a typical aftermarket ECU application would include Engine Coolant Temperature (ECT), Intake Air Temperature (IAT), oxygen sensor, Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP), Mass Air-Flow sensor (MAF), and so forth. Analog inputs are usually 0 to 5 volts, but may include 0 to 15+ volts (such as battery voltage input).
You could mount a potentiometer in the driving area to adjust EGR, HHO, or temperature threshold (for coolant fan, vaporizer, or HVAC) for testing, then (referencing data logs) eliminate the pot and just program in your set points. Analog inputs could be temperature — including thermocouple for exhaust temps, position sensors, pressure sensors, or even accelerometer sensors (MEMS). This can give you “eyes and ears” on your custom devices.
Older vehicles were mostly equipped with Narrow Band oxygen sensors (NB O2s) With a Stand-Alone ECU you can upgrade to a Wide Band sensor (WB O2) for lean-burn cruise. GM used this strategy right from the factory on vehicles destined for Australia and some other parts of the world, and typically achieved at least 20% better fuel economy over the North American versions of the same vehicle.
Analog Outputs
This is a tricky one, as analog outputs would be from a Digital-to-Analog Converter (DAC), which is mostly a reference voltage, unable to do much work. The Pulse-Width Modulation function can create the appearance of an analog output. (See below.)
Pulse-Width Modulation (PWM)
PWM offers analog type control with digital hardware. The digital output will turn ON and OFF several times per second. How long it is ON versus how long it’s OFF is called the Duty Cycle (DC%). The switching frequency is high enough that the net result is almost like varying the output voltage in an analog fashion. If you power an LED with PWM, varying the DC% from 0% to 100%, the LED would start OFF, then gradually get brighter until fully on; the same net effect as if you simply fed the LED through an analog potentiometer.
PWM strategies allow varying fan speeds, adjustable EGR, theater lighting (the LED example), adjustable HHO control, and many other uses. You could read an analog input (like TPS) and tie the result directly to a PWM output (like an HHO cell). You could also set a trip point for an analog input (temperature on the CTS) and activate a 50% DC (for a cooling fan), then at a higher trip point 75%, etc.
Tables
With a modern ECU, “Tuning” is accomplished by changing values in X-Y Tables. Fuel and ignition timing tables will usually be 2-dimensional, with RPM on the X-axis and Load on the Y-axis. A common Table size is 16 X 16 cells; or 256 total cells. Often you can change that to something smaller like 12 X 12. You would loose resolution, but you may find tuning easier with fewer cells. You can also set the range between cells. If you never rev above 4500 RPM, having a Table capable of 8000 RPM leaves half of the Table useless to you.
In addition to the main fuel and spark timing tables, there will be numerous Compensation Tables (Comps). Sometimes they are 2-dimensional with an X and Y axis, but often they are simply a single dimension array. Dwell compensation for battery voltage would look at battery voltage on the X-axis, and the cells would be additional ignition coil dwell to compensate for lower voltage. Comps would also include additional fuel% for cold-start (the “choke” function), additional ignition timing for EGR%, ignition timing versus barometric pressure, Idle Air Control (IAC) compensation for AC, power steering pressure, or alternator load.
Data Logging
Data Logging is the process of taking several snap shots of various inputs and/or outputs per second while driving. You can then review the data from the safety of the side of the road (or kitchen table). That slight stumble you cannot seem to isolate can be easily spotted when reviewing the Logs. Lean spots, ignition timing induced detonation spikes, and other conditions can be discovered in the data.
You can specify which inputs and outputs you want to record for your session. This does 2 things; first, you aren’t loading up your available memory with useless information, allowing for longer sessions. Secondly, you can focus on the data that’s important to you without swimming through a sea of distractions. You can also choose the resolution; how many snap shots you need per second. If you need to see high resolution of an event that happens quickly, or if you simply want to see trends over a longer period of time, it is under your control.
The data will be displayed on a time line. You can play back the data in real time, at a slow rate, zero in on a specific frame, and increment in either direction one frame at a time. An anomaly that took 1 millisecond to happen can be scrutinized at your leisure, with modern microcontroller accuracy. Each frame will identify what cell of your chosen Table is active, so you know which one to change. Data can be viewed digitally (just a number), as a gauge (usually a design of your choosing), or graph format. You can set the scale — what are the highest and lowest values — so the data falls within a suitable resolution.
Data Logging takes the process of Tuning into the 21st Century. In the old days, Tuning meant driving, changing something, then driving again to see if it got better or worse. A competent Tuner was someone with a finely calibrated “Butt Dyno” (could detect subtle changes by the seat of the pants). Most newer ECUs feature an Auto Tune algorithm. You fill in your Target AFR Table, and drive it. The Auto Tune software will fill in your Fuel X-Y Table for you.
Other Considerations
Most folks reading this won’t (and probably should not) opt for a Stand-Alone ECU. It represents a steep learning curve on several fronts. Wiring it in will be a serious undertaking, requiring many hours. Improper wiring ranks in the top 2 causes of issues. Something as simple as routing a sensitive CPS wire too close to an ignition coil can cause a no-start condition (or it almost wants to start, but doesn’t). It may require custom brackets for a crank trigger, where precision spacing becomes critical. You may need to replace your factory sensors with ones compatible with the ECU, or add sensors not originally equipped.
A non-factory engine controller may cause you grief come inspection time. Different states have different rules. While installing your new ECU, the vehicle will be out of commission. Can you afford to do without it for a month or maybe more? Even after you get the engine started, there will still be a lot of time spent tuning the tables. Until you get things close, plan on taking the laptop everywhere you go to collect data logs. Plan on spending evenings reviewing logs and making changes to tables. Expect to make changes to primary tables that should have been made in a comp table, then having to go back and fix it.
Most of the online tutorials and videos are geared towards racing interests. The customer support staff for the ECU company will be well versed in racing solutions. Good luck finding help with your custom HHO controls. I had attempted to install a MOTEC very high-end ECU in a 2008 Hyundai Sonata for the X-Prize Fuel Economy Race (June of 2010, Michigan Raceway). The Camshaft Position Sensor (CMS) was mounted to the Variable Cam Timing camshaft that changed position in relation to the Crank Position Sensor (CPS). The MOTEC software needed a fixed relationship. I found the cause myself after abandoning the MOTEC. I was on the phone with their East Coast AND West Coast support staff. I sent pictures of wiring, data logs — nobody caught the real problem. MOTEC is probably one of the best ECU companies on the planet. They bent over backwards to try and help. You may find a similar lack of answers for your custom project.
If the lucrative rewards of drastically improved fuel economy outweigh the potential challenges, and you want to delve deeper, a great place to start is the online training offered by DIY AutoTune:
https://www.diyautotune.com/support/efi-tuners-guide/
They are probably the #1 sellers of the MegaSquirt line of Stand-Alone ECUs. MegaSquirt is a flexible platform with inexpensive offerings with low-level control for simple projects (MS1 v2.2 kit, $197), upwards of extremely capable ECUs with generous I/Os, canned set-ups for popular applications, and Auto Tune (MS3Pro, $1749). Technology is delivering better quality, more features, and at lower prices as time goes on. The $1749 MS3Pro is a much better product than the $7000 MOTEC I worked with in 2009. Of course, MOTEC has much better offerings today than they did in 2009 as well; just saying.
In addition to their MegaSquirt line-up, DIY AutoTune is one of the premier sellers of the Innovate Motorsports Wide Band oxygen sensor products. Innovate features their own LogWorks data logging software — for free! — so long as you use at least one of their products. This offers simple WBO2 solutions without the complexity of a custom controller (WBO2s are quite sophisticated).
DIY also offers stand-alone digital dashes. Not only can you configure the display with information meaningful to you, but can select from different designs, layouts, colors, and more. Their IQ3s series also offer data logging, CAN network interface, and additional I/Os to expand the ECU’s capabilities.
Finally, DIY can equip you with ignition coils, sensors, injectors, and other components needed to make your ECU conversion complete. If you do choose to go down the Stand-Alone path, get to know the folks at DIY AutoTune.