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Tuning of fuel injection systems

219PB

Well Known Member
I would like to start a thread on tuning of electronic fuel injection systems such as EFII or SDS. I have an EFII system and I am assuming that my questions below would be applicable to SDS as well.

Let me start by saying that I DO NOT WANT THIS TO BE A THREAD THAT BASHES ANY ONE OF THE SYSTEMS! There are several us out there that want to have a communal discussion on the various strategies around tuning the systems without all of the drama that has derailed other threads in the past.

I have an O2 sensor installed and I initially optimized the fuel flow at each RPM setting based on the air/fuel ratio readings.

With that all done, here are my questions to the group to see how you might have addressed it.

1. When I take off at 2600 rpm, my engine is developing good power but after about 30 seconds my CHT climb to 425 very quickly and keep climbing if I do not richen the mixture significantly. After I richen it, the aircraft still climbs well so I leave it there. Do others just program the ECU to richen the fuel mixture every time the engine is operating at 2600?

2. I cruise at 2300 rpm at 25 Hg and lean the engine aggressively. I am seeing 170 mph at 7.5 gph with CHT's at 380 or below. My typical practice is once I am configured for cruise, is to manually lean the mixture with the electronic knob. Then I have to return it to "normal" for the decent. Should I tune the engine to run this lean automatically at 2300?

3. When I am in the pattern and cross the number on the downwind leg, I will pull the power to idle and get some popping in the exhaust. If I richen the mixture, the popping with stop. I have been adjusting the MAP curve to richen the mixture as the MAP goes down but my plane in getting painted right now and I have not finished working it out yet. How has that worked out for others?

These are the issues that are affecting me directly at the moment. I am looking for how others have addressed these issues and would like to discuss issues that others are having. Might be something that I have not thought of yet.
 
Paul, do you have gold ECUs? If so, what version of software do you have? Can read that in the bootup screen.
 
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Paul,
Most of what you describe sounds like an engine running too lean and possibly with too much advance.

When I was setting up my EI/EFI system I fixed the ignition timing to the Lycoming dataplate until I had the fuel flows established. That way any high CHT should be a result of poor baffles or inadequate fuel flow. Later, I slowly advanced the ignition to get my desired profile. I would look at advance and fuel separately.

My AFRs are set at 12 to 12.5 at RPMs from 500 to 1500. Above 1500RPM my AFRs are set to 11.5 to 12.0 (these are recommended by my system's manufacturer).

Below is a link to a past post by Dan Horton. The part in the middle about checking your full throttle takeoff power with the mixture knob zeroed is very important.

http://www.vansairforce.com/community/showpost.php?p=1192591&postcount=10
 
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For the take off event, what is your typical AFR and ignition timing?

Sorry, forgot to finish the reply. I did not change the factory timing settings. Did not even get to that screen. I really would like to spend some time, even pay someone experienced with he tuning of these units, to provide some insight.

Was instructed to start by modifying the fuel map to get the recommended AFR.
 
Paul, do you have gold ECUs? If so, what version of software do you have? Can read that in the bootup screen.

I do have the gold units. I do not have access to the plane right now as it is getting painted. I did do an update around August with the latest firmware supplied. Will update this thread when I get the plane back.
 
14:1 is pretty lean for takeoff power so that's a contributor. Let us know what the timing is doing - that's another big one. Assuming you are a standard compression PV engine, you should be under 25 degrees total advance. What's your typical DA at your home airport?
 
14:1 is pretty lean for takeoff power so that's a contributor. Let us know what the timing is doing - that's another big one. Assuming you are a standard compression PV engine, you should be under 25 degrees total advance. What's your typical DA at your home airport?

My DA is usually 2-3K. My engine is a 360 with 8.5:1 compression. I need to get into the system to see how the timing is managed. Will do when I get the plane back.
 
I have an O2 sensor installed and I initially optimized the fuel flow at each RPM setting based on the air/fuel ratio readings.

Learn to use EGT indications also. They will remain accurate long term.

1. When I take off at 2600 rpm, my engine is developing good power but after about 30 seconds my CHT climb to 425 very quickly and keep climbing if I do not richen the mixture significantly.

What Mike and Marvin said.

2. I cruise at 2300 rpm at 25 Hg and lean the engine aggressively. I am seeing 170 mph at 7.5 gph with CHT's at 380 or below. My typical practice is once I am configured for cruise, is to manually lean the mixture with the electronic knob. Then I have to return it to "normal" for the decent. Should I tune the engine to run this lean automatically at 2300?

Tune to produce rated power for all RPM/MP combinations, with LOP set manually. LOP is reduced power "dial-a-speed" or "dial for dollars", depending on your view. The system you have will allow a rather wide choice of how far LOP you want to be. For example, I might use one lean setting for high, fast cruise, and a much leaner setting for loafing around the local area down low on a nice Sunday evening.

That said, the real issue with setting your zero knob position for LOP cruise at 2300 is how to make the transition from best power to LOP. If I understand correctly, programming a best power mixture at WOT/2600 and a LOP mixture for 25/2300 will have the system "smoothing" or extrapolating everything in between. No serious study here, but I suspect you would be undesirably lean in the 75-85% power area.

Ross, you've thought about this point more than I have. Got a scheme?

3. When I am in the pattern and cross the number on the downwind leg, I will pull the power to idle and get some popping in the exhaust.

Set whatever makes you happy. The popping won't hurt anything. Richer will make it go away, as you note. Or you could try going even leaner. Many automotive EFI's deliver zero fuel on the overrun. Might make airplane passengers nervous, but it will work ;)
 
We suggest tuning the values to obtain best power with the mixture knob at the 12 O'clock position. Lean or richen with the knob as needed from there.

I can't be sure what the OP has for ECUs since they were re-branded ones. Some have a barometric sensor, some don't.
Also, the re-branded units never offered individual cylinder trim.

14 to 1 is too lean for takeoff and climb, want to be 11 to 12 AFR.

Ignition timing has a huge effect on CHTs at high power. We've found the Magnet Position values on some re-branded ECUs are not accurate and true timing may be advanced up to 5 degrees more than indicated. Check timing with a gun to verify. Running 30 degrees is a sure way to have CHTs over 400F before you've reached pattern altitude on a warm day.

Popping with low MAP has been a common complaint on re-branded systems and one some of the directly supplied SDS units as well. The OP has this figured out- add some fuel in the MAP slots below about 10 inches. The popping is caused by an overly lean condition where the fuel doesn't ignite in the cylinder but eventually builds up enough in the exhaust to fire off with a pop.

You could also use the MAP fuel cut window to shut off fuel completely below a certain MAP. This will also get rid of the popping since there is no fuel to light off.
 
So it looks like your tasks so far are as follows:

1. Verify magnet position with a timing light
2. Adjust timing map to give you 25 degrees or less at anything more than 26 inches MP and 2750 RPM. (My 8.5 CR PV engine is set to 23 degrees at 27/27)
3. Fatten the mixture as Ross suggests.

If you are still hot after doing the above then you have a baffle problem.
 
When we were using the SDS at Reno around 2009, the pilot complained about the sensitivity of the manual mixture trim. I believe it could go +- 50% trim. I put in two dropping resistors that reduced it to about +-15%. At full power we were running over 70 GPH equivalent fuel (gas + ADI), and the knob was too touchy.

Once we had the curves were right, the knob was only used flying back and forth to Reno. We has to change the curve when the ADI mixture kept getting to almost pure alky and then only above 40? boost where ADI initiated. Up to 75? boost the rule was 1 GPH fuel equivalent per inch of boost.

The new SDS system must be a dream for the Reno pilots. Individual cylinder trim, mode switching, etc.. It requires a good pilot when testing at high power, but in a race set and forget the single power knob. Ours worked perfectly from first start.
 
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