SDS Installation and Tuning Supplement for Aircraft Applications

This supplement details differences in the installation, operation, programming and tuning of SDS units being used on aircraft as opposed to automotive applications. This is intended as a supplement to the main manuals, not a replacement. The information presented here is based on our experience with aircraft EFI systems over the last 10+ years however, people use this information at their own risk. By installing SDS products on their aircraft, users understand and accept this risk as we cannot control the installation or programming of our products.

Basic Electrical System Layout

Because the ECU, injectors and ignition systems depend on electrical power to function, we highly recommend a backup battery of at least 18 amp hour capacity be installed in case of a charging system failure. We recommend that this battery be wired independently of the main master contactor to the main buss via a switch or relay. This will allow continued flight after the main battery is depleted or in case of failure of the master contactor. Any electric fuel pumps should be wired to function in the backup mode as well. Due to the deterioration of battery current capacity over time, we recommend replacing batteries every 2-3 years.

ECU Installation and Wiring

The ECU must be mounted on the passenger side of the firewall. There is no need for cooling airflow or to rubber isolate this. The ECU must be mounted in a location where it cannot get wet. We recommend mounting the ECU with the connectors facing down. By having the wiring harnesses looping down and then up, any water running down the harnesses must drip off the low point and cannot run directly into the ECU. Do not mount the ECU less than 12 inches away from any high current/ high voltage devices like DC motors, solenoids etc. Also of concern would be close proximity to certain avionics or circuits which have pulsing current present. These precautions will help minimize possible interference.

We highly recommend running all ECU wiring away from any other wiring, preferably through a separate grommet in the firewall. Never run ECU wiring parallel or in close proximity to any other wires carrying high current or voltage or pulsing currents. If you must cross other wires, try to cross them at 90 degrees and install a short piece of rubber tubing to distance these wires slightly from each other. Tie wrapping ECU wiring to other high current/ voltage wires can cause interference in the ECU cables by inductive or capacitance coupling and must be avoided.

Wiring connections may be of the crimp or solder type. Crimp connections must be done PROPERLY with the correct tool. It is a good idea to pull test every crimp connection to check integrity. Heat shrink tubing with internal sealant or adhesive for additional strain relief and oxidation protection is highly recommended. Solder joints must be made with proper electrical solder and using proper fluxes which will not corrode joints over time. Strain relief is imperative on solder type joints to avoid vibration fractures over time. This can happen when the solder wicks up the wire and makes it rigid instead of flexible. Heat shrink tubing with internal sealant or adhesive for additional strain relief and oxidation protection should be used. The end of the tubing should progress about 1 inch past the connector end. Support wires by tie wrapping to prevent movement which could flex connections.

Poor wiring practices and workmanship are the leading cause of system failures. Be careful!

Ground and Power Connections

The ECU ground coming from the 25 pin connector should go to a chassis ground which is totally clean of any non-conducting material and SEPARATE from all other ground wires. This is a very critical connection so it should be made as reliable as possible. The Injector ground wire(s) coming from the white Molex connector are equally critical. These should go to a different chassis ground point at least 2 inches from the ECU ground point and be separate from all other ground wires.

We recommend using a separate, high quality switch to switch power to the red ECU power wire coming from the DB25 connector. Power should come from a separate breaker or fuse (2 amps) , tied to the main buss. Run this wire as directly as possible. Power for the injector harness (14 gauge red wire) should go to a separate switch, 10 amp (3-4 cylinder) or 15 amp (6-8 cylinder) fuse or breaker and then to the main buss. 16 gauge wire is recommended. Power for the F coil pack should go to a separate switch , 10 amp fuse or breaker, then to the main buss. 16 gauge wire is recommended.

System Current Draw

MAP Sensor Mounting

The MAP sensor should be mounted on the passenger side of the firewall with the nipple facing downwards. Use the two mounting holes to secure it to the structure. Do not run the MAP sensor cables close to any other wires. Connect a length a tight fitting vacuum hose the intake manifold plenum. A manifold pressure gauge may be teed into this hose.

Programmer and Mixture Knob Mounting

Panel mounting the programmer is optional but recommended as it allows monitoring of ECU sensors and parameters. The 6-32 screws in the back of the programmer may be removed along with the backplate. A stepped bracket to space the programmer face back from the panel can be attached using the threaded holes in the case. Be sure to leave space for the connection cable. The optional backlit programmer is recommended for those who night fly.

The Mixture knob should be panel or console mounted in a position where it can be easily reached for adjustment but not where it is likely to be inadvertently bumped. If a mixture knob wire breaks or the knob is disconnected, the ECU returns the default knob position to zero for safety.

Tach Signal Source

For systems using the SDS supplied coil pack or blue anodized coil driver base, the short, green wire outputs a 180V tach signal or by changing jumpers internally, a 12V signal. For systems not using the blue base such as Subaru units driving late model coil packs directly from the ECU and units with the red anodized coil driver, a 5V tach signal is available from the green wire on the main wiring harness. UMA can supply a tachometer configured for this signal. The frequency is 2 pulses per crank revolution for 4 cylinders, 3 pulses per crank rev for 6 cylinders and 3 pulses per CAM revolution for 3 cylinders.

Hall Sensor/ Magnet Mounting

The Hall effect crank sensor is the most critical sensor in the system. It must be bolted to a bracket which is very strong and stiff to avoid any movement due to vibration or mechanical forces. Our rule of thumb for the bracket strength and stiffness is that it should be strong enough to lift the engine by without distortion. Wimpy brackets can lead to running problems, coil pack resets and engine stoppage.

The Hall sensor may be mounted to either end of the engine. Magnets can be mounted in either the flywheel or accessory drive pulley. Mounting magnets into the flywheel is preferable if possible as rubber damped pulleys have been known to have the outer ring slip on occasion which will alter ignition timing, possibly to the point of engine stoppage. Magnets mounting into ferrous materials such as iron or steel must project at least 1/16 inch past the surface of the flywheel or pulley. Magnets mounted in non-ferrous materials such as aluminum may be mounted flush or projecting slightly. Magnets must be mounted with at least 60% of their length in the pulley or flywheel. Use normal, low viscosity 5 minute or 2 hour type epoxy to cement these in place. Do not use high viscosity substitutes such as JB weld for this job. These materials have been shown to fail in this application or make installation difficult. We recommend removing all oil and grease from the mounting surface before drilling. Drill dry. Clean the immediate hole surrounding surface and magnet with acetone or lacquer thinner to remove all oils. Put epoxy into the hole as well as on the base of the magnet, push down completely. Trapped air may make the magnet try to pop out of the hole. Make sure that the magnet is down all the way and that a slight miniscus of epoxy surrounds the magnet.

Improperly mounted magnets can lead to running problems , coil pack resets and engine stoppage.

Coil Pack Mounting/ Ignition Wires

The coil pack should be mounted to the firewall or engine mount with the wiring grommets facing down. NEVER mount the coil pack to the engine directly. In the case of engines with dual ignition, one magneto may be retained or both eliminated and twin coil packs used.

Suppression type spark plug wires must be used. Most carbon string and spiral wound types are acceptable. NEVER use solid core spark plug wires. Unacceptable brands are Nology and Taylor. Plug wires coming disconnected in flight will cause a serious loss in power, high vibration levels and possible high interference with the ECU causing even rougher running or engine shutdown. The plug wires should be installed with the highest possible retention methods and care. Plug wire sets which use a sealed surface to the valve cover area should have a small vent hole to relieve pressure buildup in the cavity as the air is heated and expands. This will help to prevent the plug boot from being popped off from this cause.

Fuel System

This is a very important aspect of the installation and careful consideration should be given to each part. Most EFI fuel systems operate at pressures between 34-50 psi.

With a high winged aircraft having fuel tanks in the wings, it is possible to gravity feed from the selected tank to a lower mounted header tank. From here, the high pressure EFI fuel pump(s) may be mounted below this tank to gravity feed from it. Fuel will then flow to the fuel rails, injectors and any excess fuel not burned will pass through the fuel pressure regulator to the header tank, fuel selector and selected main tank. A duplex fuel selector such as the Andair models shown below with both feed and return ports are recommended. For single high mounted tanks, returned fuel can simply be routed back directly to the top of the main tank rather than through a selector. It should be noted that all main tanks must be vented to atmosphere. It may also be possible with high mounted tanks to feed the high pressure pumps directly without a header tank but uncovering of the fuel feed lines in steep, uncoordinated banked turns should be considered if planning this approach.

Header Tanks

These serve an important function for for entrained air to exit the system from the low pressure and return system and to provide a gravity fed fuel supply to the EFI pumps. The header tank should be mounted as high as possible on the firewall with the EFI pumps mounted directly below it.

Header tanks are easily constructed from 3 or 4 inch steel or aluminum tubing. Caps are welded on each end with provisions for threaded fittings top and bottom. 4 fittings on the top of the tank and 3 on the bottom work well. A tall design is best as this allows the best chance for air bubbles to float to the top, away from the EFI pump inlets on the bottom. This design also allows good gravity feed to the EFI pumps even at extreme bank and pitch angles. The tank may be mounted in the cockpit area or firewall forward. We prefer in the cockpit as there are less possible ignition and heat sources. A forward mounted tank should be protected from heat for vapor lock and fuel boiling concerns and should be made from a fire resistant material. A drain fitting should be placed at the bottom of the header tank to check for water and for maintenance concerns. This may satisfy the requirement for a gascolator which has no real purpose for EFI installations. Check with your inspector for requirements. Tank volumes of 1 to 2 liters/quarts are more than adequate. To calculate tank volume for cylindrical tanks: tube diameter divided by 2. Square this dimension and multiply by 3.14. Multiply this figure by the length of the tube. 1 US quart equals about 58 cubic inches. The schematic and photos below shows a typical design:

For low winged aircraft with wing tanks, we recommend using either mechanical, engine driven pumps or Facet electric pumps to positively pull fuel from the main tanks, through the selector and deliver it to a high mounted header tank. From here, fuel will gravity feed from to lower mounted EFI, high pressure pumps. It will follow the same path as above. We recommend using the same Andair Duplex selector valves as above. Returned fuel must always be returned to the selected tank.

While submerged EFI pumps in the tanks have been used in some aircraft, these present a couple of possible problems:

1. A switch may have to be tied into the fuel selector to turn the correct pump on.
2. In uncoordinated banked turns and high pitch attitudes, the fuel pump inlet may become uncovered due to slosh, especially with low fuel levels. This will cause the engine to stop immediately.

For these reasons, we prefer the proven header tank layout. Fuel lines should be a minimum of 3/8 to reduce the possibility of partial blockages and ensure adequate fuel flows.

Filters

We recommend using stainless steel screen type fuel filters on the inlets of both high and low pressure pumps. Earls PN230206 are lightweight and can be easily serviced.

Pumps

For low pressure electric pumps, we recommend the Facet 40106 ones shown below. These should be shock mounted as they are quite noisy. They should also be mounted with the discharge port facing up at 45 degrees to permit vapor bubbles to rise naturally through them. The inlet ports should be below the bottom of the fuel selector valve.

For high pressure pumps, we recommend the Walbro types shown below. These are an impeller type and can be run dry for several minutes without damage unlike roller vane types such as the Bosch pumps. They are also less likely to suffer damage from debris passing though than the Bosch pumps. We have used the Bosch pumps for many years where they have proven totally reliable if fed clean fuel and never run dry.

Pumps brands we don't recommend are Delco and Carter.

If you wish redundant pumps, two of each can be mounted and wired in with separate switches. Note that one low pressure and one high pressure pump must be on at all times the engine is running.

Fuel Pressure Regulators

We highly recommend the OE regulator. If this cannot be fitted, we suggest late 1985 and up Toyota, Subaru or Honda OE assemblies. These are lightweight and extremely reliable. The vacuum/ boost reference hose should be connected to the intake manifold plenum. Most OE type regulators use a barb style fuel connection for the return port. As there is little or no fuel pressure present at this point and this connection has been well proven in trillions of hours of automotive use, we feel that this should be left as is. Connect with high quality flexible line to a bulkhead fitting and cover with firesleeve.

We do not recommend Mallory aftermarket regulators.

Fuel Plumbing

Fuel from the high pressure pump should go to one end of the fuel rail and pass out the other end through the regulator to ensure the quickest purge of hot fuel. Fuel which dead heads into injectors can cause serious hot start and running problems. On opposed and Vee type engines with twin rails, fuel should again follow a loop from the end of one rail, across the line to the other rail, then out the other end through the regulator. Steel rails are preferable to aluminum ones as they gather less radiant and conducted heat. Lines, firewall forward should be steel or stainless braided types where possible. Aluminum lines should always be covered with firesleeve.

Injectors

We prefer OE type injectors rather than some aftermarket brands. Preferred brands are Bosch and Denso. On engines originally fitted with EFI, most of the fuel system hardware on the engine, including injectors, can be retained as is. On engines not originally fitted with EFI, injectors may be mounted into the intake runners using machined, weld-in mounting bosses like those offered by Racetech. Injectors should be mounted as far away from radiant heat sources such as exhaust pipes. If this cannot be avoided, proper heat shielding should be fitted to lines and injectors to avoid any possibility of fuel boiling. If fuel boils, the engine will run poorly or stop completely.

Injectors fitted to traditional air cooled aircraft engines have to be larger than what would be fitted to an automotive conversion of similar hp. This is due to the fact that the cylinders are so large on aircraft engines and that a small injector may have insufficient flow for proper cold starting. We recommend the following flow rates:

Single cylinder displacement cubic inches

50 Use 42+ lb./ hr. injectors
75-80 Use 55-65lb./ hr. injectors
90-100 Use 72-83lb./hr. injectors

Pre-Start Checks

Always check that you have fuel pressure and no leaks before attempting to start the engine. It is also worth checking that the injectors and coil packs both have proper voltage present. Spark plug wire connections and firing order must be verified. On E and F systems, check that the magnets are SEEN for 3-4 degrees of crankshaft rotation and that air gap between the sensor and magnets is 1.5-2.5mm.

System Programming

We generally enter a starting map based on injector flow rate and cylinder size. We recommend that once ignition timing values have been properly set as per the manual and the engine has been warmed up, the first adjustments should be made to the rpm fuel value at the idle range to obtain the smoothest running. Once this value is established, we recommend making all rpm fuel values the same from idle to maximum rpm. Be sure that brakes are functioning well and the aircraft is tied down and chocked securely before running the engine.

Further tuning can be accomplished with the aid of a narrow or wide band a mixture meter to target best power air/ fuel ratios (AFR) at each rpm range or by advancing the throttle to each rpm range and turning the mixture knob. If you can turn the knob an equal amount rich and lean before roughness occurs, the mixture is probably set quite well. When using a wideband meter, we try to target the AFR around 13- 13.5 for best power. When using an SDS narrow band meter, running in the first green LED to the left is recommended. Note that the lead in 100LL avgas may foul the O2 sensors used with these meters in only a few hours. Adding Decalin lead scavenger has been shown to extend sensor life considerably.

If the engine is lean at a certain rpm range, increase the rpm fuel value in that range to correct and vice versa.

The START values control fuel enrichment during engine cranking and the first few seconds after the engine starts. A larger value at a particular temperature slot, richens the mixture.

The ENGINE TEMP values control enrichment after the START values have timed out. These values get smaller as engine temperature increases. Above about 50C/ 120F, zeros are generally entered as no additional fuel is required here to make the engine run normally.

Normally, all system programming should be accomplished with the mixture knob set straight up at the zero correction point.

MAP Sensor Calibration Differences

Only 2 possible MAP sensors are used in aircraft applications. The 1 Bar sensor is used for naturally aspirated engines, the 2 Bar for supercharged and turbocharged applications. Both are calibrated in inches of mercury absolute like a standard aircraft manifold pressure gauge rather than inches gauge as in automotive applications. As such, there are no negative values assigned. Idle MAP is around 10 inches for most engines. WOT MAP for a naturally aspirated engine at sea level will be around 30 inches. Manifold pressures of up to 60 inches may be used with the 2 Bar sensor.

Ignition Programming

Gains in fuel efficiency and power may be realized by different ignition timing settings. Ignition timing may be changed in real time with the engine at a constant power setting. With fixed pitch propellers, a change in timing which results in increased rpm, indicates a gain in power. In this way, optimal timing may be realized at various rpms and manifold pressures. This can be done on the ground or in flight. Timing may be changed with rpm and with manifold pressure. Generally we set timing at 500 rpm to around 5 degrees BTDC. 750-1250 rpm can be set at around 10-15 degrees. For aircraft engines, we recommend using the standard magneto timing values above 1250 rpm as a starting point. As manifold pressures are reduced, timing may be advanced if indicated to increase power and reduce fuel flows. For automotive conversions, above 1250 rpm, we usually increase timing by about 3 degrees per step to have total rpm timing all in by about 3000-3250 rpm. Most engines will require between 28 and 35 degrees of total timing for best power. Timing may also be retarded at high manifold pressures if desired to run lower octane fuels or on turbocharged engines. Care must be taken to avoid over advanced timing which could result in detonation and engine damage.

Safety Defaults

On aircraft applications, we program in certain default values to reduce the effect of some types of sensor failures. For air temperature correction, we program in a default value of 70 at the lower and upper extremes. This will tell the ECU to correct for 20C if the sensor fails in either an open or shorted mode. Air temperature correction charts are not generally user accessible. For engine temperature correction, zero values are entered at both cold and hot extremes to ensure no change in fuel delivery in the event of an open or shorted sensor. For manifold pressure, we program in a value of 100 at the lowest and highest ranges available. This is the approximate value used at WOT on a naturally aspirated engine. If the MAP sensor fails in the high or low range, manipulation of the throttle and mixture knob should allow continued flight. Failure of the TPS to supply information to the ECU has no effect other than to engine response during very rapid throttle openings.

Automatic System Resets

The ECU will do an automatic reboot or reset if power or ground is interrupted for any reason or if the software is not executed properly. This takes less than a ½ second. High noise spikes on the power or ground lines may also trigger a reset. When an ECU reset occurs, the programmer screen will revert to the initial power up mode screen if in another screen when it occurs.

On the 4F and 6F systems, coil protection is initiated whenever an expected trigger magnet passage does not occur within a certain time window. The coil pack microprocessor will command power off to the affected ignition channel for 5 seconds before restoring power to that coil. This will cause a serious engine miss and loss of power as 2 cylinders will not receive spark.

Emergency Operation

In the event of a charging system failure, the ECU will increase both coil charge times and injector pulse width automatically to compensate for the lower voltage present. This will keep air/fuel ratios fairly constant and help maintain coil discharge voltage. Operation at low to medium power settings should be possible down to around 8-9 volts. As battery load capacity fails off very rapidly below about 10-10.5 volts, you may only have a few minutes before the engine will start to miss and die completely.

We recommend shedding all non-essential electrical loads immediately upon detection of a charging system failure, then switching to the backup battery. The nearest airport or suitable landing spot should be steered for as soon as possible. When backup battery voltage drops below about 9.5 volts, switch back to the primary and effect a landing within a few minutes. Try to maintain your altitude until you are over your chosen landing field before starting your descent. This strategy leaves you with more options than an early descent might. Be aware that any high current devices used in the descent and landing phases may deplete your battery power below levels required to continue to supply the EMS.

The mixture knob enables you to richen or lean the air/fuel ratio +/- 50% from the programmed values. This may be useful in countering certain sensor or system failures such low fuel pressure. By adjusting the throttle and mixture knob, you may be able to restore the proper mixture to keep the engine running under certain emergency conditions.

Fault Detection

If the programmer is connected, fault codes will be displayed with the failure of certain sensors. An open or shorted air or engine temperature sensor will display ERR codes in gauge 1 mode in place of the temperatures. If the ECU detects a missed magnet on the crank sensor, ERR will replace the rpm reading in Gauge 1 mode. ERR codes may be cleared by pressing the +10 button. If they reappear, they should be investigated and fixed before flying. The MAP sensor reading should be around 30 inches with the ECU turned on and the engine not running at sea level. This reading will be somewhat lower at higher elevations.

Normal Operation

When proper programming is completed, best power operation will be automatic, with the knob in the zero or straight up position. It should be part of the checklist to ensure that this is so. We generally recommend that takeoff, circuits and initial climb is performed with the knob at 0%. Extended climbs may be leaned via the knob to your target EGT. Upon leveling and setting cruise power and rpm, the mixture can be leaned to your target EGT. Before descending, mixture should be set richer again. It should be noted that the ECU will automatically adjust the mixture as manifold pressure changes due to varying altitude and varying manifold pressure based on mapped values. The knob however has overriding control so its position is important to proper engine operation.

We recommend that you never run a fuel tank dry with EFI. This is very hard on the fuel pumps and the design of the fuel system may make re-priming of the system difficult and time consuming under certain conditions. If you have a feed problem on the tank you have just switched to, the other empty tank leaves no options. We recommend switching over to the other tank when the currently selected one is down to ¼. This leaves the option to continue flight for some time on the original tank if there is a problem with the new tank.

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