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Over the past year, I have seen a drop in WOT RPM.  Previously, the RPM would be 5800 at full throttle, now it is only 5600.  Checking things this morning I am only getting 35 inches of manifold pressure.  I do not have the TCU software, cable or even a Microsoft notebook.  What should I check or how can I boost the manifold pressure up to 39 inches?  Thanks for any suggestions.

  • Re: 914 Low Manifold Pressure

    by » one month ago


    One of the first things I would do is to re-calibrate the throttle position sensor. For that you will need the TCU software.

     


  • Re: 914 Low Manifold Pressure

    by » one month ago


    Ryan, Thanks, I will probably have to fly somewhere to get that done.  I was out playing with it and it seems that the controller is targeting 35 inches.  The wastegate stays closed as I advance the throttle then opens a little as I get to 5500 RPM and hunts for a position then stays at that slight open position. Randy


  • Re: 914 Low Manifold Pressure

    by » one month ago


    My 914 experience has been that the motor doesn’t like running between 100% and 115% and searches for a way out. Look for a pressure leak at the clamps and hoses or possibly recalibrate the TPS.


  • Re: 914 Low Manifold Pressure

    by » one month ago


    Sam, It is certainly a different animal above 5500 RPM.  I do not have any way to access the TCU program here but I will check the hoses today.  Here is a link to a video of my runup that I did yesterday.  https://www.youtube.com/watch?v=ORCIpJ4qAYg I was advancing the throttle steadily and some of the interesting things I noticed was a kind of flat spot in acceleration around 5000 RPM; then a major change in everything at 5500 RPM.  The RPMs jumped to 5600, the Manifold pressure jumped to 35 inches; the Fuel pump pressure went way up.  I can not correlate this video with the one I took of the wastegate solenoid but in that video, this is about when it opens the wastegate, hunts a little then settles in about 20% open.  I do not know if all this is normal.  Hard to decipher TCU information in the manual. Randy


  • Re: 914 Low Manifold Pressure

    by » 6 weeks ago


    Well, two computers (Chrome Book doesn't work) and two serial cables (first had wrong data set) and I was able to recalibrate the TCU throttle response.  Strapped down the Magni and warmed it up.  With great expectations I advanced the throttle to get the exact same response of 36 inches manifold pressure.  Actual was 35 something inches.   Watching the video showing RPM and manifold pressure it looks like the pressure reduces a little to keep the RPMs from climbing above 5660 or there about.  Spending much more time reading about the TCU than I would like, it has the capability to reduce the manifold pressure starting at 6000 RPM.  Could the RPM sensor for that capability be off?  Can it be inspected?  The display color change occurs at 5500 RPM so that seems to be working.


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