LS3 Misfire

Discussion in 'Chevy' started by TXFlyGuy, May 26, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. May 26, 2019 #1

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    No...not my plane.

    But another T-51 owner has the newly installed LS3 engine. With a Link G4+ Xtreme ECU. The engine runs perfect, for about 15 minutes of flight. Then after getting warmed up, it misfires. No one seems to have a clue why.

    My money is on:

    1. Coil pack that fails when hot, so plug doesn't fire
    2. HT lead that has a break and resistance increases when hot, so plug doesn't fire
    3. Faulty injector

    Anyone here care to take a stab at a diagnosis?

    IMG_0533.JPG
     
  2. May 26, 2019 #2

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,639
    Likes Received:
    3,269
    Location:
    Memphis, TN
    Do these ECUs have diagnostics? Codes? You could ohm each coil pack in hope you could see one off from the rest. If not you would either have to buy 8 coil setups and 8 plugs and change all at once or make 8 flights moving one new coil pack to each position. I would change all plugs. Plugs are cheap. Same process if you do injectors.
     
  3. May 26, 2019 #3

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,382
    Likes Received:
    2,306
    Location:
    Rocky Mountains
    Not me. Done too much of trying to diagnose intermittent problems.
    You have 2 options that work. One is to just start replacing parts that have a high probability of being the cause until the problem goes away, as TFF mentioned. This works but can get expensive and time consuming .... or you can get lucky and hit it the first try with your SWAG.

    The second method, and the one I prefer, is to gather data. Hook up a lap top and digital oscilloscope. Go fly and record the data real time. Note the time the event starts and then look at the data leading up to that point. You may still not be able to pinpoint the cause if it is something like a bad plug that can't be directly monitored. But you can eliminate a LOT of variables.

    The second presumes that you have done the standard ground tests of the individual components, like ohms/volts/frequency, while shaking the wiring bundles and looking for intermittent signals. One can also bake things like coil packs and injectors in an oven to simulate operating temperatures.
     
  4. May 26, 2019 #4

    delta

    delta

    delta

    Well-Known Member

    Joined:
    May 27, 2011
    Messages:
    1,923
    Likes Received:
    191
    Location:
    Brookside Utah
    Plug color may indicate offending cylinder.
     
  5. May 26, 2019 #5

    rv6ejguy

    rv6ejguy

    rv6ejguy

    Well-Known Member

    Joined:
    Jun 26, 2012
    Messages:
    3,749
    Likes Received:
    2,788
    Location:
    Calgary, Alberta, Canada
    Just about any modern aftermarket ECU should have data logging capability which should quickly show you what's causing the issue. Almost certainly not an injector as they never have heat related issues fitting these symptoms.
     
    TXFlyGuy likes this.
  6. May 26, 2019 #6

    narfi

    narfi

    narfi

    Well-Known Member

    Joined:
    Feb 23, 2016
    Messages:
    751
    Likes Received:
    376
    Location:
    Alaska
    I've never worked on auto conversions, but on traditional engines assuming you dont have individual cylinder monitoring,

    Emmediatly after shutdown from running hot and rough, hit each exhaust flange at each cylinder with a laser temperature sensor to find the one not firing.
    Alternatively run the back of a bic pen across the exhaust as close to each cylinder as possible. The good cylinder exhausts will be hot enough to melt the plastic and lubricate the pens path so it slides easily against the metal, a cold cylinders exhaust will not and the pen will scrape against it instead of sliding.
     
    spaschke and Vigilant1 like this.
  7. May 26, 2019 #7

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    Thanks. Yes, the ECU has many channels of data available, and should make a diagnosis fairly easy.
    When we get ready to fly (paint shop this week), hopefully we will not have any of these issues.
     
  8. May 26, 2019 #8

    Toobuilder

    Toobuilder

    Toobuilder

    Well-Known Member

    Joined:
    Jan 20, 2010
    Messages:
    4,447
    Likes Received:
    3,246
    Location:
    Mojave, Ca
    So are we discussing your buddies airplane in this thread, or yours? I can't keep track of the problems you are trying to solve. And I'm with Ross... This problem should be a 5 minute job to solve with the data logging your buddy (or you) have. If this was an OX5 in a Jenny, that would be different.
     
  9. May 26, 2019 #9

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    Long story. Not my plane, but an LS3 engine. I am just trying to help Jim out, and get the plane flying soon.

    Thanks to all of you for your input!
     
  10. May 26, 2019 #10

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,858
    Likes Received:
    1,844
    Location:
    North Carolina
    It could be a zillion things. Without looking at it, hard to tell. Somebody who knows engines needs to troubleshoot it. Or throw parts at it. If you can reproduce the problem on the ground, it will be easier.
     
    TXFlyGuy likes this.
  11. May 26, 2019 #11

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    Now I am really scratching my head...the folks at Titan claim the data log is absolutely no help in diagnosing the problem.

    Does this make any sense to you? Seems odd to me.
     
  12. May 26, 2019 #12

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,639
    Likes Received:
    3,269
    Location:
    Memphis, TN
    My truck will tell me which cylinder. My wife’s car too. She had one recently on the way to her moms. She had it checked at an autozone and I told her to buy the part and I will come down and change it
     
  13. May 26, 2019 #13

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,639
    Likes Received:
    3,269
    Location:
    Memphis, TN
    It went intermittent and was ok the rest of the trip, but when she got back I changed it. The information should at least tell the bank.
     
  14. May 26, 2019 #14

    Kyle Boatright

    Kyle Boatright

    Kyle Boatright

    Well-Known Member

    Joined:
    Nov 12, 2012
    Messages:
    792
    Likes Received:
    430
    Location:
    Marietta, GA
    What's Titan's relationship to the engine?
     
  15. May 26, 2019 #15

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    It is the FWF LS3 package, sold and installed by Titan Aircraft.
     
  16. May 27, 2019 #16

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,382
    Likes Received:
    2,306
    Location:
    Rocky Mountains
    Yes, it can be the case that the data log provides no clues. It depends on the detail and accuracy of the data log. A modern EFI using dual wide band O2 can almost give you a cylinder by cylinder real time data stream. I'm guessing that this aviation EFI doesn't even use O2 sensors? If so then the rest of the system is likely to be just as simple and the data stream may not capture the error.

    in this case you are back to the old school (pre OBD II) days of using a digital multi-meter and a breakout wire harness.

    If it's a Titan installed engine package - it's kind of their problem? Without detailed knowledge of the system architecture all we can do is guess.
     
  17. May 27, 2019 #17

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    Correct, O2 sensors not used, because the fuel is 100LL. Initial flight tests were done with the O2 sensors (on the test engine), then the fuel ladder was programmed.

    On the surface it would seem that it is Titan's problem. But there is more to the story, and it is a long story. Not going into details here.
     
  18. May 27, 2019 #18

    rv6ejguy

    rv6ejguy

    rv6ejguy

    Well-Known Member

    Joined:
    Jun 26, 2012
    Messages:
    3,749
    Likes Received:
    2,788
    Location:
    Calgary, Alberta, Canada
    Link is a high end automotive ECU and it has data logging capability.
     
  19. May 27, 2019 #19

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,382
    Likes Received:
    2,306
    Location:
    Rocky Mountains
    Understood. Been there done that.

    Get as much documentation as you can dig up on the FI system. Wiring diagrams and sensor specific specifications will help you reverse engineer the system. Unless you go down the parts swapping path you have to know the system details if you are to have any hope of doing proper diagnostics. You may even find it helpful to add some temporary stand alone sensors, like a wide band O2 sensor on each bank, just for the diagnostic value.

    Edit: Just saw rv6ejguy's post. If it is indeed a well known system with data logging ability then the above probably is not relevant.
     
  20. May 27, 2019 #20

    TXFlyGuy

    TXFlyGuy

    TXFlyGuy

    Well-Known Member

    Joined:
    Apr 26, 2012
    Messages:
    1,493
    Likes Received:
    436
    Location:
    Republic of Texas
    Without O2 sensors, will the data generated be adequate to diagnose and remedy issues like this?

    I am considering running with O2 sensors if this is a big help.

    The Link G4+ offers advanced closed loop system lambda strategy operation, and dual bank lambda control.

    30 general purposes tables.

    We hope to get efficient fuel flow, avoiding the use of O2 sensors if possible. This would dictate open loop operation.
     
    Last edited: May 27, 2019

Share This Page

arrow_white