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Thread: Engine troubles for beginner FS team

  1. #1

    Engine troubles for beginner FS team

    Good day, everyone. I am Aditya Trivedi, part of the powertrain department of Camber Racing, an FS team based at SRM University, India. We are using a KTM engine for this year's car, the one used for Duke 390 here (it's a single). The engine has been giving us trouble we can't quite figure out. Here is how it goes:
    The intake system for the car is previous year's design, and features two throttle bodies, one just after the air filter for throttle actuation, and another just above the engine head to put the fuel injector in (we didn't have time to measure the fuel injector angle so this was a quick fix). As per the rules, only the outer throttle body is controlled. We are facing difficulty in getting the engine to rev; the engine doesn't rev beyond 7500RPM. Until then it seems to be running fine, but after reaching this engine speed it starts pulsing very slowly (somewhat as if it's hitting the rev limiter, but a lot slower). It goes as low as 4000RPM during these pulses, recovering to 7500RPM again before repeating. It randomly backfires as well, and if one lets off the throttle completely the engine stalls. After a lot of trying to modify the intake (it had a lot of leaks so we did our best to seal them) we decided to put on the stock airbox and remove everything else. The problem continued. Then we thought that maybe the MAP sensor wasn't functioning like it should (I read that it can be affected by backfiring), so we replaced that. The engine now starts pulsing at 6500RPM instead of 7500RPM, with no other change in operation even though the intake system is now stock, essentially. What would you suggest we do in diagnosing this problem? We have prepared the following possible list of faults:
    1. Carbon buildup on the spark plug
    2. Dirty fuel line/injectors (we are thinking of buying injector cleaning fluid for the same, what would you recommend?)
    3. Low fuel line pressure
    4. Incorrect exhaust length, leading to wrong resonance pulses.

    We have obtained values from the MAP sensor, and I am listing down the max and minimum indicated pressure values at different engine RPM:
    Idle - 37.875kPa, 101.41kPa
    3000RPM - 34.6kPa, 95.71kPa
    5000RPM - 36kPa, 100kPa
    7000RPM - 37.875kPa, 103.62kPa
    These are the peak points obtained, the graph reads almost like a sawtooth waveform. If anyone would like those, I'd be glad to PM you.
    That being said, are these values normal for a single cylinder engine? Please keep in mind that the MAP sensor is in the throttle body mounted just above the engine head using the stock airbox, and the engine is being run without any load whatsoever.
    Thanks for reading this through, looking forward to a positive response to my first FS forum post.


  2. #2

    Are you guys using a stock ECU or are you running an aftermarket ECU?
    Wayne State University Formula SAE [Warrior Racing]

    2015 - Technical Advisor (Engine - Calibration Lead) "Old Man Jenkins"
    2013-2015 - Powertrain Director (Engine - Calibration /Electrical Lead)
    2012-2013 - Engineering Captain (All the things)
    2011-2012 - Cooling/Exhaust Lead

  3. #3
    Aditya, I'm not an engine expert but have worked through some of the issues you are describing.
    Mo here has the right question, which will determine a lot of other question possibilities. Answering that will help the most.

    Whether it is stock or not several other things to check:
    sensor wiring. Is your crank sensor twisted and shielded? If not, it may be picking up noise which really affects it at high rpm and causes lost synchronization, misfiring and possibly out right dying. Another thing may be is if it is looking for an oxygen sensor signal (from the exhaust) and if there is any leak or sensor mishandling on that end. This would cause more (or less) fuel to be dumped into the engine which may flood the engine, making it unresponsive (if it's super rich) [also something Mo should check out after seeing your car this weekend] or if your timing is set incorrectly which will cause what may seem to be random intake backfires.

    Beyond that, pretty much every parameter on the engine could make this condition happen under the right settings. However, the above are the most common from my experience.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  4. #4
    Yes, its a stock ECU, made by Bosch. There is no shielding for the wires (the stock harness came without them as well before we took it apart to remove the immobiliser and other unnecessary sensors). We shall look into this. Timing is stock, then, so we expect no problems on a stock intake setup.
    We're getting a wideband AFR sensor with display soon so shall be able to confirm on whether the engine is running rich or lean.
    We're looking to get it running on a Performance Electronics PE3 ECU, but since we're facing this issue right now even on the stock airbox I thought it prudent to rectify it before moving onto another harness and ECU.

  5. #5
    What does the plug look like? If you operate in this unstable regime for a few seconds then abruptly shut off ignition/injection and pull the plug, you'll at least have a starting point to see whether you've got too much or too little fuel
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  6. #6
    Thank you for your replies.
    Unfortunately we don't have the part required to get to the spark plug right now (we can only open the cam cover). Local dealers aren't very co-operative in us even requesting to buy them. This is on our list of things to check, and I hope to update on this as soon as possible.

  7. #7
    It sounds like you are very tight on resources so I'll suggest a simple test that may help. If the fuel system has a return line give the hose a quick pinch when the engine is struggling to spike the fuel pressure up. If the speed picks up you have a fuel supply issue or a sensor that is preventing proper fueling command from the ECU. You can also try the opposite (pinching the supply line).
    It should go without saying but do NOT use sharp tools to do this.

  8. #8
    Senior Member
    Join Date
    Oct 2009
    San Antonio, TX
    Removing the spark plug without a special spark plug socket is easy. Use the appropriate size deep-well socket to loosen the spark plug. Then use the plug wire boot/coil, a piece of rubber hose, or a pencil magnet to extract the spark plug. For installation, use any of the three to get the threads started (this is the tricky part). Then tighten with the previously used socket.

    It is downright wrong that the KTM dealership does not want you checking your race engine's spark plug and this is a troubling part of Indian culture. Humans need to keep agency over the most basic elements of their things. I recommend the book "Shop Class as Soulcraft" http://www.nytimes.com/2009/05/24/ma...pagewanted=all. It might be a good resource for the team to have to deal with the cultural issues regarding getting your hands dirty.
    Matt Birt
    Engine Calibration and Performance Engineer, Enovation Controls
    Former Powertrain Lead, Kettering University CSC/FSAE team
    1st place Fuel Efficiency 2013 FSAE, FSAE West, Formula North
    1st place overall 2014 Clean Snowmobile Challenge

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