Knowledge Check · Fuel-Injected Engine and Starting

reSource Course · High Performance & Complex · Module 3

Fuel-Injected Engine and Starting

How the Bonanza's fuel injection works, and how to start it cold, flooded or hot.

The F33A's Continental IO-520 is fuel-injected. There is no carburetor: an electric auxiliary fuel pump primes the engine, and the right starting technique depends on whether the engine is cold, overprimed or hot. This module covers how the injection system moves fuel, the normal and overprimed starts, the hot start, and the starter and warm-up limits from POH pages 4-8 to 4-10. Plan on about eight minutes.

Start Lesson 3.1 Test Yourself
3Lessons
5Interactive labs
14Check questions

Which Start Is This?

Interactive

    Key points only. Run every start from the checklist in your airplane's POH, Section IV.

    Module 3 · Fuel-Injected Engine and Starting · Lesson 1 of 3

    Lesson 3.1

    How Fuel Injection Works

    Pumps push fuel to a nozzle at every cylinder. The throttle and mixture decide how much gets there.

    FAAPHAK Ch. 7, Aircraft Systems · AFH Ch. 12

    A carburetor mixes fuel and air in one place, then sends the mixture down the intake pipes. A fuel injection system skips that step. It sprays fuel into the intake port of each cylinder, just ahead of the intake valve. Every cylinder gets its own measured share, and the flow is continuous while the engine runs.

    The PHAK describes six basic components. Follow the fuel from the tank to the cylinders:

    1. Auxiliary fuel pump
      Electric. Supplies fuel under pressure for starting and for emergency use. In the F33A, this is how you prime.
      Aux
    2. Engine-driven fuel pump
      Turned by the engine. Supplies fuel whenever the crankshaft is turning.
      Pump
    3. Fuel/air control unit
      Meters fuel according to the throttle and mixture settings. At idle cut-off, it stops fuel here.
      Meter
    4. Fuel manifold valve
      The distributor. Splits the flow evenly among the cylinders.
      Split
    5. Discharge nozzles
      One in each cylinder's intake port. Sprays fuel into the incoming air.
      ×6
    6. Fuel pressure/flow indicator
      Shows what the system is delivering. You watch it while priming.
      Gauge

    Trace the Fuel

    Interactive
    Fuel injection system, tank to nozzles Tank and selector Auxiliary fuel pump OFF Engine-driven pump STOPPED Fuel/air control unit Throttle: idle MIXTURE RICH Fuel manifold valve Splits flow six ways Discharge nozzles, one per cylinder
    Auxiliary fuel pump
    Engine
    Throttle
    Mixture
    Pressure fromNone
    Fuel at nozzlesNo

    A simplified layout for learning the flow, not a plumbing diagram. Try the aux pump on with the engine stopped, then move the mixture to idle cut-off.

    What It Gains, What It Costs

    PHAK advantages

    Why Injection

    Less risk of evaporative (carburetor) icing, better fuel flow and distribution among cylinders, faster throttle response, precise mixture control, and easier cold-weather starts.

    PHAK disadvantages

    What to Watch

    Difficult starts when the engine is hot, vapor lock during ground operation on hot days, and trouble restarting an engine that quit from fuel starvation. Lesson 3.3 covers the hot start.

    Injection removes carburetor ice, not all induction ice. Snow or impact ice can still block the air intake, which is why fuel-injected engines have an alternate air source. Module 4 picks up power and mixture management from here.

    Remember

    The aux pump primes. The mixture decides whether fuel reaches the cylinders.

    At idle cut-off, no fuel gets past the fuel/air control unit, whichever pump is running. That fact is the key to clearing an overprimed engine.

    Check Yourself

    Module 3 · Fuel-Injected Engine and Starting · Lesson 2 of 3

    Lesson 3.2

    Normal and Overprimed Starts

    Prime with the aux pump, watch the fuel flow, and protect the starter. If you flood it, cut the fuel and open the air.

    POHF33A Section IV, 4-8 to 4-9FAAPHAK Ch. 7

    The Normal Start

    With the throttle and mixture set as the POH checklist calls for, you prime by running the auxiliary fuel pump. Watch the fuel flow indicator. When the flow peaks, turn the aux pump off. The engine now has fuel in its intake ports, and the starter does the rest.

    1. Set up per the POH checklist
      Throttle, mixture, prop and switches as Section IV lists them.
      4-8
    2. Aux pump on until fuel flow peaks, then off
      This is the prime. Leaving the pump on longer floods the engine.
      Prime
    3. Engage the starter
      No more than 30 seconds of cranking in any 4-minute period.
      30 s / 4 min
    4. Warm up at 1200 rpm or less
      Until oil temperature reaches 75°F. Lesson 3.3 explains why.
      ≤ 1200

    Protect the Starter

    The starter is an electric motor built for short use. Long cranking overheats it, and the POH limits cranking to 30 seconds in any 4-minute period. If the engine does not start, stop cranking, let the starter cool, and work out why before you try again. Repeated long attempts usually mean the engine is either underprimed or overprimed.

    Starter Duty Timer

    Interactive
    4 min ago321Now
    Clock0:00
    Cranking, last 4 min0 s
    Available now30 s

    The bar shows the last four minutes. Each block is a period of cranking. Try three 10-second attempts in a row, then one more.

    The Overprimed Engine

    Too much prime leaves the cylinders too rich to fire. The cure is to stop adding fuel and pump air through the engine. With the mixture at idle cut-off, no fuel passes the fuel/air control unit, so cranking with the throttle open draws air through and clears the excess. As the engine fires, you bring the throttle back to idle and the mixture to full rich so it keeps running.

    Clear the Overprime

    Interactive

    Tap the steps in the POH order. Two of the cards do not belong.

      Overprimed start, POH 4-9. Confirm the wording against the checklist in your airplane.

      Remember

      Flooded? Cut the fuel, open the air, crank.

      Mixture idle cut-off, throttle open, crank. As it fires: throttle idle, mixture full rich. And never more than 30 seconds of cranking in any 4 minutes.

      Check Yourself

      Module 3 · Fuel-Injected Engine and Starting · Lesson 3 of 3

      Lesson 3.3

      Hot Starts and Warm-Up

      A hot engine fills its fuel lines with vapor. A cold engine needs its oil warmed before you add power.

      POHF33A Section IV, 4-9 to 4-10FAAPHAK Ch. 7

      Why Hot Starts Are Hard

      After shutdown, the cooling air stops but the engine stays hot. Heat soaks into the fuel lines and the manifold valve, and some of the fuel turns to vapor. The PHAK lists this as the main drawback of fuel injection: hard hot starts and vapor lock on hot days. The engine may not start, or it may start and then stumble as vapor bubbles reach the nozzles instead of liquid fuel.

      The POH hot-start procedure on page 4-9 deals with that vapor. The step that sets it apart: once the engine starts, run the auxiliary fuel pump briefly to purge the vapor from the lines, then turn it off. Fly the rest of the procedure from the POH checklist, and keep to the same 30-seconds-in-4-minutes starter limit.

      Pick the Start

      Interactive

      Decide which procedure each situation calls for.

        There is no single temperature that makes a start "hot." Engine heat soak after a recent flight is the usual trigger.

        Warm-Up Limit

        After any start, the POH limits the engine to 1200 rpm or less until the oil temperature reaches 75°F. Cold oil is thick and slow to reach the bearings, cam and cylinder walls. Keeping the rpm low until it warms limits wear while the oil is still getting where it needs to go. In cold weather that can take a while, so plan for it before you call for your clearance.

        Warm-Up Check

        Interactive
        OilCold
        RPM limit now1200

        The warm-up limit only. Run-up is covered in Module 8, and cycling the prop in cold weather in Module 5.

        Remember

        Hot engine, expect vapor. Cold oil, 1200 rpm or less until 75°F.

        After a hot start, a short run of the aux pump purges the vapor. After any start, keep the rpm low until the oil comes up to temperature.

        Check Yourself

        Module 3 · Fuel-Injected Engine and Starting · Knowledge Check

        Knowledge Check

        Module 3 Knowledge Check

        Eight questions in the style of your instructor's oral review, each tagged with its source. Pass mark: 80% (7 of 8).

        Score0 / 8
        Next: Module 4 · Power and Mixture