Fuel Pump and Manifold Pressure Question

Shempinator IIIShempinator III
in General Discussion

Hello all,

I posted a question about a year ago regarding a high fuel pressure reading on take off. Last year I had a new fuel pump installed on my 1977 Turbo Arrow III.

Red line is 19 psi and I was getting 23-25 psi at 41 inches. Reducing power to 33 inches on climb out the pressure drops below red line and the rest of the flight is normal. After several adjustments from my mechanic, the pressure reduced to 22-23. Still over red line. After a few more attempts with no success, I decided to deal with it later.

Fast forward one year and my annual is due. I added the high fuel pressure to my list of squawks. After completion of the annual, I test flew the plane and the fuel pressure is still 23 psi on take off power. In addition, now I couldn't reach 41 inches mp. With the throttle pushed all the way to the stop, I only get 38 inches. This is at sea level. After rotation and climb it did creep up to 41 inches at 97 knots. My mechanic made adjustments on the fuel pump several times and after four test flights. No change.

Any suggestions on this issue is greatly appreciated.

Thanks,

Todd S.

Comments

  • planewrenchplanewrench

    Todd my first question would be when you say the mechanic is making adjustments does he have a test gauge setup or if he just going by what he's seeing in the cockpit? TCM has specific requirements for gauges to set fuel pump pressures it's not just a tweak here and a tweak there. Carl

    50yrs A/P IA DAL A/C inspector. 172N Rotax IRMT 912/914

  • Shempinator IIIShempinator III

    Hi Carl,

    I'm pretty sure the pump was set with gauges after install. Since then, while in for annual this year, not sure.The recent adjustments are based on pressure readings in the cockpit. Small turns of a screw then test fly.

    And since the annual MP is affected. I never had the push the throttle to the stop on T/O.

    Todd

  • Tom_JaxTom_Jax

    For the MAP issue, has your mechanic gone back to look at the waste gate? Make sure it's not coked and is opening fully. Also, worth looking for an induction leak. Both of those could potentially cause lower MAP.

    Sounds like putting the gages back on the fuel system and resetting to baseline would be a wise course of action. Ideally, you want to do that on a moderate day-temps not super high or low, and reasonable humidity.

    Tom Jackson

    PA28RT-201, N3022U

    Tappahannock, VA (KXSA)

    A&P/IA, Private Pilot, IR/A

  • planewrenchplanewrench

    Todd, Tom took the words out of my mouth. Fuel pump setting either on or it's not. There's no tweaking. I'm going to assume you have the altitude compensating fuel pump too. If your maintenance group is not totally familiar with doing this setup you need to take it to a shop that does. All air lines and upper deck reference lines have to be in perfect shape for everything to work correctly.. Carl

    50yrs A/P IA DAL A/C inspector. 172N Rotax IRMT 912/914

  • Shempinator IIIShempinator III

    Not sure if the pump is altitude compensating but the part number is 649368-26A1.

  • Shempinator IIIShempinator III

    Thanks for the info guys,

    I will let you know what I find out.

  • Shempinator IIIShempinator III

    Problem solved,

    The Manifold pressure issue ended up being the nut on the V-band on the intake side of the turbo was lose. The nut was torqued and safety wired. Test flight was successful with MP up to 41" quickly.

    Thanks for the help everyone.


    Todd S.

  • planewrenchplanewrench

    Excellent Todd. Carl

    50yrs A/P IA DAL A/C inspector. 172N Rotax IRMT 912/914

  • empanninempannin

    That is a lucky find as a full exhaust leak there would be catastrophic. Now that it is sealed did they go back and repeat the fuel pressure adjustments with the gauges?

    There are a couple intake leak checking smoke generators that also work on the exhaust side. I have found it invaluable for tracing small leaks in cars, boats and planes. It will not only generate smoke with plain mineral oil but it also pressurizes the line so it will push out of even the smallest of openings.

    The one below is the same one I have. It does need a small 12V battery to make it work. This one has the range of adapters to fit into the induction and exhaust system. You will see leaks at all the slip joints but should not have any leaks at the v-bands or exhaust manifold flanges.

    These things really shine on older automotive systems with a rats nest of aging plastic fittings and rotting vac hoses. I have struck out with ultrasonic testers where the smoke test quickly found it.

    image.png


    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

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