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Thread: IO360 A1A fuel servo

  1. #1

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    IO360 A1A fuel servo

    greetings all, I am flying a BCSC in Botswana with a IO360 A1A in it, been struggling with achieving full power and my AMO thinks the Fuel Servo needs a service/replacement.

    so I have a Bendix RSA-5AD1 - 2524213-10 ...... but google says this variant is for a IO540 260hp engine..... and that a IO360A1A should have a 2524054-11

    can anyone help me with what the differences would be? engine builder tells me that "fuel servo is the same" but I can't see how a 6 cyl 260hp engine can use the same fuel servo as a 4 cyl 200hp engine?

    I have tried googling what the differences are but no luck so far.

  2. #2

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    Here's the source of information for you. These guys know fuel injection.

    Airflow Performance INC.

    111 Air Flow Drive

    Spartanburg SC 29306

    864-576-4512

    864-576-0201(Fax)

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    N1PA
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    thanks Guys, chatted to Don at Airflow Performance, very helpful, apparently the different part numbers are only for the peripherals like the linkages and fittings, the body of the fuel servo is all the same base unit RSA-5AD1. so now the headache begins trying to get a little chunk of metal halfway across the world
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    What's yours doing that needs fixing and how did you recognize it?
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    I'm with Stewart on this before you ship it half way around the World. What is your full power fuel flow? This can be checked by disconnecting the fuel distribution lines, placing the ends in equal sized jars and running the fuel pump with the mixture and throttle wide open. Then do the same thing with the nozzles in the jars. Do they flow an equal amount for each nozzle? Perhaps you only need to clean the nozzles?
    N1PA
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  7. #7

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    we aren't 100% sure what exactly is wrong with the engine, we have several symptoms:
    1. CHT's and EGT's we have higher temps on #3 (which is often the case with these engines) but the real problem is that we set up the engine in cruise and not 10 minutes later one of the temps will change significantly (not talking the usual small changes because of lift/sink)
    2. Fuel flow irregular - at a specific power setting fuel flow will jump around, pressure is stable at around 24psi, when you put on the electric fuel pump fuel flow goes up briefly and then settles at a LOWER fuel flow than it was reading before
    3. irregular starting, I know the injected engines can be tricky but usually you can figure out a system that works, we keep having to figure out new tricks.
    4. irregular full power rpm at take off
    5. irregular Manifold pressure readings, and unusually low manifold pressure readings
    6. higher fuel flow readings than we should be getting for this engine - as mentioned above also irregular
    7. leaning is no an even process, you can screw out the mixture, temps slowly climb, then suddenly within a ⅛th of a turn the CHT starts climbing and won't settle till it is 40+F higher, I know there is always a "hump" after which it gets a lot more sensitive but this seems extreme to me.

    so now you will all be saying to yourselves "but many of those symptoms can be a myriad of other problems", and I agree.... but many of them point back to an irregular fuel delivery into the piston. which is why we have decided to get at least ONE element on the engine looked at and reset to where it should be and then start going through the checks again, otherwise we will just be chasing our tail forever.

    we have already done the following:
    - correct baffling, now we have relatively good control over our CHT's and can keep them under 400, which wasn't the case before
    - corrected lower cowl outlet - now developing enough differential pressure to cool
    - moved oil cooler to behind #3 on the baffle and turned oil cooler around (both pipes came out bottom of cooler) so it can self bleed any airlocks - oil cooling now much better (we know that this might be part of the reason why #3 cyl is 20F higher CHT than the others, but at least now we have stable CHT and OIL temps.

    we have subsequently found a company in South Africa (only 800 miles away) that has parts for our Bendix RSA5AD1 fuel servo and we have shipped our unit to them, then at least we will have one element that should be reliable. will update what the result is when we have it back in the plane.

    @Skywagon8a - our full power fuel flow indicates 58-62ltr/hr (15,5-16,5Gal) on our G3X and we have had our nozzles cleaned in a ultrasonic machine and tested them, their delivery is not exactly the same but we have our fuel divider sent in with the servo to be checked.

  8. #8
    skywagon8a's Avatar
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    Quote Originally Posted by bodumatau View Post
    5. irregular Manifold pressure readings, and unusually low manifold pressure readings
    This could be a result of an irregular fuel flow that will be corrected when your servo and divider are returned.
    Be sure to let us know of your results when you get it back together.
    N1PA
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    Quote Originally Posted by skywagon8a View Post
    This could be a result of an irregular fuel flow that will be corrected when your servo and divider are returned.
    Be sure to let us know of your results when you get it back together.
    - exactly my thinking, will give y'all an update when we get it back together.
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  10. #10

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    fuel servo and overhauled fuel divider are back and have been installed.
    - our shop down in South Africa that overhauled the fuel servo said to us that it seemed in very good condition just the settings were completely off -> this rang a little warning bell in my head.... because I KNOW that one of our problems is that we are getting very high fuel flows at full power (sometimes over 60ltr/16.5Gal)
    - so now we are seeing LOWER overall fuel flow at full rich but coupled with this our troublesome cyl#3 is now running slightly over 400 at cruise, which we dont want.

    since our cyl#3 is ALWAYS 25-35F higher than the next highest cylinder and the EGT is also ALWAYS higher than the next highest by about 40F I am now thinking it might be a manifold leak

    any other suggestions?.

    oil temps are stable around 180-190 with an OAT of 75-90F and go up to 185-200 with an OAT of 90-110

    our manifold pressure reading is 16" at 2300rpm at 3200ft ASML and 75F, is this not too low?
    although we are seeing 23" at full throttle at take off
    at idle we see very low values, 2" for 800-900, 4-5" for 1000-1100
    MAP sensor is on cyl#3

  11. #11
    skywagon8a's Avatar
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    Quote Originally Posted by bodumatau View Post
    fuel servo and overhauled fuel divider are back and have been installed.
    - our shop down in South Africa that overhauled the fuel servo said to us that it seemed in very good condition just the settings were completely off -> this rang a little warning bell in my head.... because I KNOW that one of our problems is that we are getting very high fuel flows at full power (sometimes over 60ltr/16.5Gal)
    Without knowing the exact numbers for this model engine. those fuel flow numbers sound about right.

    Quote Originally Posted by bodumatau View Post
    - so now we are seeing LOWER overall fuel flow at full rich but coupled with this our troublesome cyl#3 is now running slightly over 400 at cruise, which we dont want.
    At what OAT? Other than a high OAT you may have leaned the mixture too much or the baffles need some attention. Can you get a 100 degrees EGT rise when you lean the mixture? That is considered to be a minimum. Has your engine been fully broken in?

    Quote Originally Posted by bodumatau View Post
    ..since our cyl#3 is ALWAYS 25-35F higher than the next highest cylinder and the EGT is also ALWAYS higher than the next highest by about 40F I am now thinking it might be a manifold leak
    This would be possible if you had a carburetor, but you don't. Your injected fuel is mixed with the intake air downstream of a possible air leak location.

    Quote Originally Posted by bodumatau View Post
    oil temps are stable around 180-190 with an OAT of 75-90F and go up to 185-200 with an OAT of 90-110
    This is good.

    Quote Originally Posted by bodumatau View Post
    ..our manifold pressure reading is 16" at 2300rpm at 3200ft ASML and 75F, is this not too low?
    although we are seeing 23" at full throttle at take off
    at idle we see very low values, 2" for 800-900, 4-5" for 1000-1100
    MAP sensor is on cyl#3
    This indicates that you have a low pitched prop. Which in turn raises more questions about your over 400 CHT since you are not using maximum available power with that engine. Look at your baffle design. Are there ramps behind the nose bowl openings up towards the center of the cylinders? Have you restricted open space behind the starter ring gear where the air can bypass directly underneath? Is the baffle up tight against the back of #3 or is there some space so that the cool air can get down lower on the cylinder head prior to flowing between the cooling fins?
    N1PA
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  12. #12

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    Quote Originally Posted by skywagon8a View Post
    At what OAT? Other than a high OAT you may have leaned the mixture too much or the baffles need some attention. Can you get a 100 degrees EGT rise when you lean the mixture? That is considered to be a minimum. Has your engine been fully broken in?
    our OAT's are generally between 70F and 100F (airborne OAT's, on the ground we see up to 115F, we have spent a LOT of time on our baffles, got the whole front area behind the prop very well sealed up, front end of #1 cylinder and back end of #3 cylinder have nice gaps to let the air through to the lower quadrant. Before we sent our Fuel servo for service we could, at cruise we would see about 1040 full rich and could lean out to over 1400 if we wanted to, but that would push CHT's up so we never leaned more than about 1170 depending on load and OAT. Engine now has 149 hours on it so I think it is broken in.


    Quote Originally Posted by skywagon8a View Post
    This would be possible if you had a carburetor, but you don't. Your injected fuel is mixed with the intake air downstream of a possible air leak location.
    I disagree, if the fuel servo feeds a certain amount of fuel to the divider because of the air pressures it is seeing in the throttle body and then the induction tube of cyl#3 leaks air INTO the system then that cylinder will have too much air and run too lean. it will also mean that not all the air is being drawn through the fuel servo so it isn't feeding enough fuel into the system exacerbating the problem even more.

  13. #13
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    Quote Originally Posted by bodumatau View Post
    I disagree, if the fuel servo feeds a certain amount of fuel to the divider because of the air pressures it is seeing in the throttle body and then the induction tube of cyl#3 leaks air INTO the system then that cylinder will have too much air and run too lean. it will also mean that not all the air is being drawn through the fuel servo so it isn't feeding enough fuel into the system exacerbating the problem even more.
    Not so. You are mixing carburetor and fuel injection trouble shooting issues. The fuel is evenly distributed from the flow divider depending on the orifice size of the discharge nozzles which are in the intake port of the cylinders. Unless your injector nozzles have been changed from the originals, they all have the same sized orifice. Thus the mixture entering each cylinder is identical regardless of any induction tube leakage. Have you cleaned your nozzles? Sometimes just a tiny microscopic piece of dust can distort the smooth even flow. Sometimes you can look into the nozzle with the light and magnification just right and see a little hair across the flow path. That's enough to make a difference.

    This company sells tuned injectors. https://gami.com/gamijectors/gamijectors.php You can run tests to determine which nozzles need to be changed. Perhaps your #3 nozzle needs a larger orifice?
    N1PA
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  14. #14

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    Gami...was going to suggest it... sounds like youve checked all the trouble shooting boxes... if you dont have any other modifications to the baffles or modifications to increase the differential pressure, and no changes to the exhaust system.... then go the Gami route. I dont know if Gami adjusts the flow rates on anything other than their injectors? If they do youll only need to send in your injectors once for calibration along with the data from your engine monitor. If not...buy a set of Gami injectors...fly the airplane...then send the injectors back to Gami for calibration. Odds are number three needs a bit more fuel to cool that cylinder...


    Sent from my iPad using Tapatalk Pro
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  15. #15
    skywagon8a's Avatar
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    Alternatively to the GAMI route, you can go to https://airflowperformance.com/. This is what I did. They modified my nozzles with removable orifices so that they can be fine tuned for much less expense than GAMI. Contact airflow and they will give you the procedure for determining the size.
    N1PA
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  16. #16

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    Airflow performance can provide nozzle restrictors and has instructions for how to begin the balancing process on their website, but that’s generally for fine tuning to run lean of peak. You could explore increasing fuel to #3 but in warm ambient temps 400* doesn’t sound too alarming and 25-30* variance in EGT is no cause for concern. Diverting some of the airflow from 1 and 2 to improve cooling at 3 and 4 sounds like the place to start. https://airflowperformance.com/wp-co...structions.pdf

    PS- ensure that you have stand-off space to allow airflow down behind #3. Your issue may not be fuel related.
    Last edited by stewartb; 11-29-2019 at 05:47 PM.
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  17. #17
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    Quote Originally Posted by bodumatau View Post
    ...any other suggestions?.
    This is a good article on checking your fuel nozzles and how to determine if they have different flow between them. The author is retired from Lycoming.
    https://generalaviationnews.com/2019...=TPOA-20191202
    N1PA
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  18. #18

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    Quote Originally Posted by stewartb View Post
    PS- ensure that you have stand-off space to allow airflow down behind #3. Your issue may not be fuel related.
    yes we definitely have the standoff behind #3, this was our very first try to bring #3 in line, we have now also made a flow director (see thread "lower cowl scoop shape")

    Quote Originally Posted by skywagon8a View Post
    This is a good article on checking your fuel nozzles and how to determine if they have different flow between them.
    we have done this and have very close fuel flows across all 4 cylinders, did the test twice

    since we have had our fuel servo serviced our fuel flow is much lower. - before we were seeing around 1030EGT's cruising at 2300rpm full rich, now we dont see below 1250EGT at the same settings.
    our next step is a slightly larger fuel nozzle in #3, we hope to test this today, having some heavy rainstorms in Maun at the moment so might not be able to test today.
    Last edited by bodumatau; 12-10-2019 at 03:47 AM.

  19. #19

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    With a baffle standoff and how low you mounted a 13 row cooler on the aft baffle I'm surprised #3 stays within 25*. Throwing more fuel to it addresses a symptom, not the problem. My opinion anyway. Good luck.

  20. #20
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    Quote Originally Posted by bodumatau View Post
    ...since we have had our fuel servo serviced our fuel flow is much lower. - before we were seeing around 1030EGT's cruising at 2300rpm full rich, now we dont see below 1250EGT at the same settings.
    our next step is a slightly larger fuel nozzle in #3, we hope to test this today, having some heavy rainstorms in Maun at the moment so might not be able to test today.
    It is clear that something has changed. You are aware that the actual EGT number is meaningless? The only published EGT limits are TIT (turbine inlet temperatures). You don't have one of these.
    The following was sent to me from Airflow performance as a procedure for determining the proper sized fuel nozzles.

    Nozzle Tuning Data

    The basis of nozzle tuning is to get each of the cylinder EGTs to peak at the same fuel flow. Your aircraft must be equipped with EGT information on each cylinder and fuel flow information. A digital flow meter is preferred. Adjusting nozzle size to get all the EGTs to read the same number is not correct and can in fact damage the engine.


    To gather correct data for nozzle tuning, set a cruise power setting. Typically 24 MAP and 2400 RPM. Set the mixture to be 0.5 GPH richer than peak on any cylinder. At this setting record all the EGTs for each cylinder. Lean the mixture 0.2 GPH and record all the EGTs again. Lean the mixture an additional 0.2 GPH; record all the EGTs again. Continue leaning the mixture 0.2 GPH and record the EGTs until all the cylinders have peaked.


    An alternative method although not as accurate is to lean each cylinder to peak and record the fuel flow at that point. You will get the same data, but since the EGT reacts slower than the leaning process you may go past the peak and not know it. This is especially true if an engine monitoring lean find function is used. We get more accurate data taking the EGT data manually. If you use an automatic data acquisition function, allow 30 seconds or so at each fuel flow setting so the EGT value can stable out.


    After the data is taken, we determine which nozzles to change to get all the cylinders to peak at the same time. You will notice that the EGT number at peak may not be the same for each cylinder, THIS IS NOT IMPORTANT. The cylinders that peak first (higher fuel flow) are the lean ones; the cylinders that peak last (lower fuel flow) are the rich ones.


    Getting all cylinders to peak within 0.2 GPH is ideal.
    N1PA

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