Eagle EMS Technical FAQ

Eagle EMS Technical / Installation FAQ

Click on any of the links below to go directly to a specific question or topic. Or click on this link to go to the first item and then scroll through the list.

1) What is the "mixture control potentionmeter?"

2) Do you send the potentiometer with the wiring, or do I provide it later?

3) What are the four pipe thread taps on the throttle body used for?

4) What sort of lines do I use for the MAP runs to the ECU?

5) I have already mounted my ECU on the cabin side of the firewall. How do you recommend routing the MAP lines through the firewall?

6) How do I measure four CHTs in a four-cylinder engine when the Eagle system uses two CHT sensors? Also, which cylinders should the Precision Eagle probes go into?

7) For MAP display, do I randomly select one cylinder pipe fitting hole, or do I tee off one of the MAP inputs to the ECU?

8) For a key switch, do I use a single contact, or do I need some sort of Left/Right switch?

9) In the installation manual, is there any schematic to show how things are supposed to be connected?

10) On which side of the firewall do you suggest I install the ECU?

11) The Eagle Q&A mentions that a fuel flow may be available from the injector pulse width and fuel pressure. Is this something I can display, or do you have in mind some other display for it? If so, will there also be a fuel totalizer and when do you plan to have it ready?

12) Should the electric boost pump be operated continuously, just for takeoffs, or what? Is the idea behind using it to better avoid vapor lock?

13) I was told I needed an alternate air supply and a regular carb heat system for the alternate air. When would this be used?

14) Instead of two 5-amp circuit breakers, can I use two 5-amp ATA style fuses in a fuse block? Is there some reason to have these accessible?

15) Is there any value to installing a wide-band O2 sensor in one of the exhaust pipes, and which pipe should I install it in?

16) Notes on the Eagle EMS Battery

17) Notes on the ECU

Q: You mention a "mixture control potentiometer" in the installation manual. What is it, what does it do, and how is it used?

A: This potentiometer is a leaning function. It will lean the mixture from the point where the calibrated fuel flow in the Eagle is set. This setting is a percent change and this change will be maintained regardless of throttle position or altitude. The exceptions are if the engine is too cold, the engine is too hot, or the BAP minus MAP is less than 0.5".

Q: Do you send the potentiometer with the wiring, or do I provide it later?

A: We provide it to you when we ship the harness to you. The potentiometer has its own short harness with connectors. These connect to the ECU sensor harness that Precision Airmotive supplies. The customer provides the distance from the ECU to the potentiometer when ordering the custom harness.

Q: There are four pipe thread taps on the throttle body. I know two are for manifold pressure, but which two and what are the other two taps for?

A: The two manifold pressure (MAP) taps are located on the flange of the throttle body. The two tapped ports midway up the throttle body are the air inlet temperature (IAT) ports. The air temperature sensors are shipped with the harness.

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Q: What sort of lines do I use for the MAP runs to the ECU? It needs to be flexible to accommodate engine vibration, so hard aluminum line is not recommended. However, the fittings are flares, as used on hard aluminum lines.

A: You may use a standard, non-collapsible, #4 low-pressure hose. Hose & fittings example: Aeroquip Hose, P/N 306-4; and two end fittings, P/N MS27404-4D.

Q: I have already mounted my ECU on the cabin side of the firewall. How do you recommend routing the MAP lines through the firewall?

A: In most instances, the ECU will be mounted on the engine side of the firewall. However, in either application, we recommend running flexible lines to the ECU. One option is non-collapsible hose (Aeroquip P/N 306-4) from the throttle body to a bulkhead fitting, through the firewall, and then a non-collapsible #4 flexible hose to the ECU. The main thing is to end up with a tight seal.

Q: The Eagle system uses two CHT sensors in a four-cylinder engine. I want to measure four CHTs using a GRT EIS 4000. How do I accomplish this? Also, which cylinders should the Precision Eagle probes go into?

A: The Precision Eagle requires two of the cylinder CHT probe holes. The owner may use four annular CHT probes (the type that are installed under the spark plugs), or two annular and two probe holes for the engine monitor.

We recommend that the Eagle's left-side CHT sensor go into the hottest cylinder and the right-side sensor into the second-hottest cylinder.

Q: For instrumentation in the cockpit for MAP display, do I randomly select one cylinder pipe fitting hole (where Lycoming says you may put a primer), or do I tee off one of the MAP inputs to the ECU?

A: We recommend using a cylinder priming hole.

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Q: For a key switch, do I use a single contact, or is there some sort of Left/Right switch required to test the ignition on both sides independently during run-up?

A: We recommend a standard aircraft ignition switch. Since the Eagle is a dual ignition/fuel system, you may use any type of switch you prefer. However, you must be able to switch to the left ECU, the right ECU, or both.

Q: In the installation manual, is there any schematic to show how things are supposed to be connected? To the Eagle battery, annunciator, ignition switch, etc.?

A: The schematic will be included in the installation manual in the upcoming revision. UPDATE (3/11/08): The installation manual, which includes the schematic, is now available for download from our website.

Q: You say that the ECU can be installed on either side of the firewall. Which side do you suggest, considering all the wiring? It looks like there would be a lot less wiring going through the firewall if the ECU was installed on the engine side of the firewall.

A: Taking into consideration all the wiring, and that the ECU was designed for heat within the engine compartment, the ECU should be mounted on the engine side of the firewall in a place where the temperature will not exceed 175°F. The ECU should be mounted flat up against the firewall because the firewall functions as a heat sink.

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Q: You mention in the Q&A section that a fuel flow may be available from the injector pulse width and fuel pressure. Is this something I can display on my GRT EIS 4000, or do you have in mind some other display for it? If so, will you also have a fuel totalizer? When do you plan to have it ready?

A: Part of the harness supplied by Precision has the necessary wires for RPM and fuel flow in the cockpit. With these extra outputs, we will supply the wires and create the correct signal that will adapt to your panel display. Contact us for specific information on the use of the wires.

Q: You mention that a 20-35 psi electric boost pump should be used to feed the Lycoming engine-driven pump. Is the boost pump to be operated continuously, just for takeoffs, or what? Is the idea of using a high-pressure boost pump to better avoid vapor lock?

A: We recommend using the boost pump for startup, takeoffs and landings. The rest of the time, it is there in case the engine-driven pump fails. The minimum required fuel pressure is defined in the installation manual and is dependent upon the required fuel flow. For recommendations regarding fuel flow and fuel pressure, contact the engine shop installing your Eagle.

Q: I was told that I needed an alternate air supply, and to install a regular carb heat system for the alternate air. When would this be used?

A: An alternate air system should be installed similar to a fuel-injected aircraft. A carburetor heat system is not recommended. The alternate air is needed if your filter becomes blocked or plugged. Typically, alternate air draws air from inside the lower cowling.

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Q: Instead of two 5-amp circuit breakers, would two 5-amp ATA style fuses in a fuse block be OK? Is there some reason to have these accessible, maybe to turn one of them off at a time to check that both sides of the ECU are working?

A: Since most aircraft have resettable circuit breakers, we designed the system around these breakers. We do NOT recommend using fuses instead of breakers. If a problem occurs and you have to troubleshoot while in flight, resetting a breaker is much more practical than changing a fuse.

Q: I plan to install a wide-band O2 sensor in one of the two exhaust pipes. Is there any value to this? Which pipe should I install it in?

There is value because the O2 sensor tells you more information about what the engine is doing. The O2 sensor can be used to help calibrate and monitor the system.

Notes on O2 sensors:

Leaning using RPM, MAP, EGTs, and engine smoothness/roughness still apply. See the engine manufacturer's manual.

The ultimate system would have one O2 sensor in each pipe. However, in general practice, a single sensor is placed at a point in the exhaust system where it can assess as many pipes as possible. Follow the sensor manufacturer's instructions regarding the placement of the sensor inside the pipe.

Only use a wide-band sensor for proper airflow resolution. Whenever the engine is running, the sensor must be powered or it will become fouled.

Notes on the Eagle battery

The Eagle draws approximately 1.6 amps. The battery you get will be determined by the power draw and how long you would need to continue flying in the event of main electrical system failure.

The Eagle is always powered by the Eagle battery. It is charged from the main bus. The bus and the Eagle battery are in parallel. Under certain circumstances, the PMU will automatically disconnect from the main bus when voltage drops below the voltage of the Eagle battery.

It is important to have a fully charged battery in good condition.

Notes on the ECU

There is a small hole on the ECU box that looks like a phone jack. This is the port for a cable that goes to the output of an O2 meter. If you purchase an FTO or Innovate brand O2 meter, this cable is usually included. The idea is to record O2 data along with all the other parameters at the same time so you see everything.

If you do purchase an FTO or Innovate, you need to let the engine shop know so the ECU will be configured correctly.

If you want to plug the port, you may use a 1/8" rubber plug. You might put a dab of RTV on the outside of it to hold it in.

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14800 40th Ave NE Marysville, WA 98271 (360) 651-8282