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Erratic drivability at around 100آ°C

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  • Erratic drivability at around 100آ°C

    My engine runs as I believe it should at an indicated 80-85آ°C, which is what I typically warm it up to before driving, and is also the temperature it settles in to when cruising on a highway unimpeded. In traffic or low speed driving on surface streets, it goes up to an indicated 100-105آ°C and intermittent drivability issues arise. It doesn't seem to want a steady throttle, and if more throttle is introduced gradually, it balks - sounding like it is sucking air, but with insufficient fuel - and then when given a bit more throttle to stop it from stalling, it lays down power suddenly and all at once (not so good in the typical 25 MPH zone). Whenever I check it, fuel pressure is consistent at 62-65 psi, but I don't know if that is the case when the stuttering occurs because the fuel pressure regulator and gauge are in the engine bay. I initially thought this to be a low-rev mapping issue, and it may be that, but it could be something else. Any ideas?
    | | Sean

  • #2
    Just a guess.....check the location of the air temperature sensor (I assume you have one). If there is heat soak from the engine bay at low speeds it may lean out the mixture too much.

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    • #3
      Yes, there is a temperature/pressure sensor on the bottom side of the intake housing. Hmmm...
      | | Sean

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      • #4
        I would try to disconnect it and see what happens. The ECU should revert into a default value for the IAT (Intake Air Temp). If you are having a temp-compensation mapping issue at 100C, it should change with the sensor disconnected, which will prove the case.

        /Magnus F.

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        • #5
          Sure enough, that did it. The "sucking air" symptom at temperature disappeared completely with the sensor disconnected. The sensor is located in the bottom-center of the air filter backplate/tub, and is about an inch above a coolant line. Relocating the sensor to top-center should be easy enough - the length of wires to the sensor leads me to believe that was the original intention anyway.




          The car still doesn't like steady throttle at any temperature, particularly at low speeds - it wants to either accelerate or decelerate - but I believe that is a mapping issue.

          Thanks a million Gert and Magnus! <thumbs up smilie goes here>

          edit -- also added a couple ounces of Sta-Bil to the fuel tank as a preventative measure to ensure any water in there is eliminated, at Doug's suggestion. I'm not a math major, but I figure that's gotta be good for around two pounds of cure. :)
          Last edited by Sean; July 22, 2011, 12:35 PM.
          | | Sean

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          • #6
            Sean

            I'd put in 1/2 the bottle of the Sta-bil.

            More won't hurt, too little might not get it all.

            Doug

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            • #7
              If you can get the password for your map from Caterham, I can most likely take care of the steady throttle issue.

              /Magnus F.

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              • #8
                Good news: Just borrowed a Windows laptop, and the software on the CD that came with the ECU/USB-CAN bus adapter/cable/CD package already has Master level access.

                Bad news: The software could not "see" the ECU no matter what I tried, it is EasiMap 5 rather than the more current 6, and the XP laptop is a bit slow. Slow laptop is tolerable, and release 5 instead of 6 is workable, but getting it to connect is a must. I intend to call the original supplier on Monday for suggested solutions.
                | | Sean

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                • #9
                  Follow-up

                  Tried again today. When the USB cable is plugged into the laptop with the software already running, Windows puts up a "New Hardware Found" message that reads something like "USB-CAN (985)", and then it goes about loading the drivers from the CD. So it seems the laptop has been able to see the ECU all along, but the Easimap 5 software cannot seem to communicate with it, as it alternates showing "USB-CAN bus" with a black background, and "Searching" with a yellow background in the relevant screen area. I tried every possible port configuration, two different Win XP laptops, and even downloaded Easimap 6 (password-protected free version) just to check connectivity, and still got the same result. Time for a wtf call to Cosworth.
                  | | Sean

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