LS3 Misfire

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

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  1. May 27, 2019 #21

    rv6ejguy

    rv6ejguy

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    Another issue with the T51 installations is that you can't easily fit wideband sensors due to the short, stack exhausts. This has been a big problem since the Suzuki and Honda V6 eras with regard to tuning EFI systems on them.
     
  2. May 27, 2019 #22

    TXFlyGuy

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    It seems that Titan has been able to work around this, operating in open loop mode. Apparently we are restricted to this on the LS3.

    Are there any good options in dealing with the short exhaust stack, and O2 sensors, or the complete absence there of?
     
    Last edited: May 27, 2019
  3. May 27, 2019 #23

    Hot Wings

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    I keep forgetting you have stubby exhaust to deal with. Unfortunately I don't know of any practical way to use an O2 sensor with these. Back flow makes measuring O2 accurately very hard. Even an upstream leak in the exhaust flange gasket can cause problems.

    You might have to make friends with the local "fast and furious" type street racers. Some of them are actually pretty good with FI.

    Of course, this problem could still be only indirectly related or unrelated to the FI.
     
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  4. May 27, 2019 #24

    Winginitt

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    My suggestion is, if you are gooood friends, let him borrow the complete coil packs off your engine and do a complete swap...brackets and all. That will tell him if he has a coil problem, and verify that you probably won't. Its a simple unbolt unplug swap that should take little time and save him some money. I also agree with the suggestion that he look at the spark plugs for any sign of what may be happening. Don't just change them. Mark them for each cylinder and then compare them for any difference in color, shape of electrode, etc. Do one thing at a time. Also, describe the miss he is getting. Any backfire, intermittent(random) miss or steady miss, or recurring but steady miss.
    By that I mean, does the miss seem completely random with no discernable rhythm. Is it steady in that once it starts it is continuous and doesn't stop, or does it miss for a while...then normal for a while....then miss for a while? Also, what AOA ?

    Before changing anything, I would see if the miss can be replicated on the ground. Tie the plane to something and try to replicate the rpm and time before the miss starts. You can film the exhausts to look for any noticible change in whats coming out, and as someone suggested, use a lazer temp sensor to check exhaust temp while running.If you don't get any good results on the ground, put a camera(s) on the plane
    to monitor the exhaust stream and engine monitoring guages. That can be reviewed later on the ground.

    Remember that even though its controlled by a modern ECU, old fashioned mechanical problems can be at fault too. He also might want to contact the manufacturer of the ecu and ask for suggestions. They may not be able to tell him what is wrong ...but they may be able to tell him why their system is not telling him anything useful...ergo what to look for that isn't monitored by their system. It can be something as simple as a loose ground wire or poorly made connection . Those coils are usually pretty reliable as are the crate engines.The biggest unknowns are the ECU,the wiring and the connectors and the fuel system.
     
  5. May 27, 2019 #25

    TXFlyGuy

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    The most suspect place might be the wiring. But if that were the issue, why would it run just fine for the first 15 minutes?
     
  6. May 27, 2019 #26

    Voidhawk9

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    Things warm up, gaps expand, contact is lost... had this happen to me in cars in different ways over the years. Once car would not start at all during the day but was fine at night. Dry joints in the main relay closed up in the cold of night! Similarly, had a misfire due to cracked HT lead once. Was fine when cold or low power, but warm it up and use high power, misfire.
     
  7. May 27, 2019 #27

    tailwind

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    How much time on the engine? My v8 likes to build deposits on the exhaust stems that make for miss fires. Marvel Mystery oil keeps it away.
     
    Last edited: May 28, 2019
  8. May 27, 2019 #28

    TXFlyGuy

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    Brand new engine.
    They just discovered a cam sensor lead was loose. Titan will ground test it tomorrow. Hope this is the problem!
     
  9. May 27, 2019 #29

    Hot Wings

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    Doesn't quite add up. This should have shown up as an error code, or have been noticed on the data log at the very least.
     
  10. May 28, 2019 #30

    TXFlyGuy

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    Should know more tomorrow.
     
  11. May 28, 2019 #31

    bmcj

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    Actually, assuming it is only one coil pack failing, you would only need 4 new packs and three flights to isolate. Change 4 to decide which 4 had the problem, then change 2 of the 4 out on the bank with the problem to narrow it down to 2, then change 1 of the 2 out to isolate which one has failed.
     
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  12. May 29, 2019 #32

    TFF

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    My car will tell you the cylinder as does my wife’s as it just had this problem. My wife’s old Maxima, two cars ago, would only tell the bank. After I changed the bank, it threw a different code. Ohm miss match. I had to change the other because they all want to be the same. My luck it would always be the last flight combo. I don’t mind points, and I should have stocked up on a hundred of them for my older cars. Now they are like vacuum tubes. Expensive.
     
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  13. Nov 4, 2019 #33

    TXFlyGuy

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    Ok...they did a complete engine swap, brand new LS3 installed. All problems fixed. The engine and plane are now flying, and will be ferried to Los Angeles in a few days.
     
  14. Nov 4, 2019 #34

    Winginitt

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    They were unable to identify the problem ?
     
  15. Nov 5, 2019 #35

    Dan Thomas

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    The ultimate most-expensive parts-throwing repair. Replace an entire engine and its systems to see if the problem goes away.:)
     
  16. Nov 11, 2019 at 2:54 PM #36

    TXFlyGuy

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    They tried everything and finally did the engine change. Problem fixed.
     
  17. Nov 11, 2019 at 4:56 PM #37

    akwrencher

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    Sometimes, you have to know when to fold ''em..........
     

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