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Stumble at 3000 RPM 2-10 degrees throttle.

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  • #16
    I would not use compressed air as that just pushes the dirt deeper into any place it can reach.

    Best to vacuum it out. If you have an air compressor you can get a cheap venturi vacuum generator from Harbor Freight.

    I also have a setup you can use that has a catch tank built in.

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    • #17
      The idea was to make a solution by pouring gasoline/rubbing alcohol into the bore and stirring it with compressed air.

      I will, however, buy a venturi vacuum at Harbor Freights today.

      /Magnus F.

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      • #18
        Ok. I poured gasoline in cyl 2 and 3, stirred it with compressed air, and vacuumed it out.

        This turned out to be quite an efficient way to rid your cylinder of soot since what came out was quite brown. Afterwards, when I looked down the spark plug hole, it was shiny and nice in there. No major particles found in the filtered gasoline that I evacuated.

        Finally, contrary to Doug's recommendation, I blew out the cylinders with compressed air using a long thin tube inserted into the plug hole

        A subsequent compression test yielded 130 psi on all cylinders, including those that were not contaminated.

        I'll do a leakdown test later this week to be sure, but it seems like there is no engine damage.

        I'll plug the hole that let the grit in, reassemble everything, change oil, and call it a day.

        /Magnus F.

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        • #19
          I didn't say it wouldn't work, just that there were more surefire but time consuming ways to be sure it was clean.

          I don't really know how big a chance you took. If it doesn't scratch the bore you saved lots of work pulling the head.

          I don't want to know if it didn't work.

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          • #20
            Glad to read about it all working out. What did you use to plug the hole?
            | | Sean

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            • #21
              I just did a leakdown test of all cylinders. They are all in the 4-5% range, which means happy engine.

              The hole was temporarily plugged with a piece from an IKEA child gate and a plastic cap. And by temporarily I mean eternally.

              /Magnus F.
              Last edited by magnusfeuer; March 5, 2013, 07:24 PM. Reason: Correct perentage. 77-78 psi in cyl at 80 psi in. I can't math.

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              • #22
                Engine back together.

                It still stumbles. The TPS is absolutely smooth all over the range.

                I'll log the RPM to see if we actually loose the signal during the stumble, which would indicate a crank sensor failure.

                /Magnus F.

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                • #23
                  I have a Windows 98 laptop with the Pectel software for the T6 datalogging if you don't.

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                  • #24
                    I may need that. Let me start off with doing a simple trace in the descpro software to see what I get.

                    /Magnus F.

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                    • #25
                      Did a run with the laptop hooked up.

                      RPM traced fine, even when the engine cut out, telling me that the crank sensor was fine.

                      However, after a while, I noticed in the ECU event log it showed that the T6 every now and then switched between 360 and 720 mode.

                      Background info: In 360 mode, the ECU does not know which stroke each cylinder is in and fires the injectors and spark plugs on both the intake and exhaust stroke. 720 mode is activated when the cam sensor reports the cam shaft's position,. thus telling the ECU which stroke each cylinder is in.

                      Each time the ECU switched between the two modes, the engine died for about 0.2 - 1.0 seconds (probably while waiting for a cam signal that never came).

                      I validated this by disconnecting the cam sensor, and the engine locked in 360 mode and ran fine.

                      Today I purchased a new cam sensor, but the problem is still there. Next step is to start to look for faulty connectors / wiring.

                      /Magnus F.

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                      • #26
                        Looks like you are getting closer.
                        When I installed the TBs and wired in the ECU I was first tempted to do sequential injection. But I could not really find credible reports beyond Internet chatter that is has a measurable advantage. So I skipped the cam sensors and left it with batch mode.

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                        • #27
                          7% increase in fuel consumption; the T6 has a compensating multiplier for 360 mode. My engine also idles differently (less smoothly?). Apart from that, no big difference.

                          I'll still track it down, though, since I don't like unknown issues in my electrical system.

                          /Magnus F.

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                          • #28
                            So I messed around with the sensor settings in the T6 ECU. After changing the trigger criteria from zero crossing to leading edge, and lowering the threshold from 625mv to 312mv, the ECU seemed to recognize the cam signal correctly.

                            My theory is that there is oxidation going on in a connector that induce resistance, thus lowering the voltage of the cam signal.

                            I'll do some more experimentation.

                            /Magnus F.

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                            • #29
                              And? Fixed it?

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                              • #30
                                That fixed it.

                                But the consequence may be noise at high rpm that will give false cam signals.

                                I've cleaned out all the connectors, but still need to get everything back together.

                                This will take a while since I will be traveling this week and next.

                                /Magnus F.

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