60
isolator is not used in series with this wire, damage to the RPM input on the EDC
could occur.
a) Action: Check that there is an Isolator(s) in line with the RPM signal wires from the
EDC.
If only one RPM channel is working, swap the wires to the EDC RPM channel
and see if the problem follows the EDC channel or the wire to the P-lead.
2. Problem: The Isolators in line with the EDC are incorrect.
a) Action: If the RPM reading is jumping high, add a “47” or “79” Isolator in series with
the existing Isolator. The signal from the P-lead is too strong.
If the RPM signal is from an electronic ignition, there should NOT be any
Isolators in the wire to the EDC. The EDC RPM input triggers at 3 volts.
7.6 Fuel Flow Problem:
Fuel Flow is measured using a Flow Transducer. Power (+10 volts on the Red wire) and ground (Black
wire) is supplied to the transducer from the EDC. A rotor in the transducer spins and produces pulses (0
to +5 volts) on the White wire. The +5 volts portion of the pulse on the White wire comes from a pull-up
resistor in the EDC. The K-factor found in the “Fuel K-Factor" screen calibrates the pulses to produce a
flow rate.
Symptom:
Symptom:
Symptom:
Symptom:
Symptom: Inaccurate readings.
1. Problem: The K-factor is incorrect.
a) Action: Check that the K-factor (found in the “Fuel K-Factor" screen) is correct for the
transducer installed in the aircraft (FT-60 red cube = 68,000, FT-90 gold cube =
33,800 and the FT-180 black cube = 22,400).
Symptom:
Symptom:
Symptom:
Symptom:
Symptom: Inaccurate, jumpy or zero reading.
1. Problem: A wire is open, shorted or mis-wired.
a) Action: Measure the voltage on the transducer wires from the EDC at the Flow Trans-
ducer. The Red lead = +10 volts, Black wire = 0 volts, White wire = + 5 volts
with the White wire removed from the flow transducer.
Ohm the Black wire to ground. The Black wire must be shorted to ground (< 10
ohms).
Rapidly tap the White transducer wire to ground. A small fuel flow reading
should show on the CGR.
1. Problem: The rotor in the Fuel Flow Transducer is blocked.
