J.P. Instruments EDM 960 Twin Primary Installation Manual - Manual (Page 36)

FAA Approved Installation Manual for the EDM-960 system Report No 909
Primary Engine Data Management System Page 36 of 46 Rev D
Date 2-6-2014
39. Trouble Shooting
1. A missing column in the display upon start up indicates the continuity check diagnostic routine has found an open
line or probe with no connection. An error message will indicate which cylinder to look at.
2. A missing column in the display during flight indicates a reading that is jumping around or incorrect. The probe is
removed from the line up to prevent false alarms.
3. A negative reading (-) in front of the number indicates reverse polarity on the red/yellow wire to probe.
4. Using an ohmmeter or continuity checker measure across the probe output leads. A good probe should be around
2- ohms and at the connector to the probe around 20 ohms.
5. Erroneous or erratic readings on one cylinder reading. Swap the suspected probe with a probe from a good
cylinder. If the problem goes to the good cylinder the probe should be replaced. If the problem remains the same, it
is in the Thermocouple hook-up wiring from the probe to the instrument or it can be in the ring terminals crimped to
the wire. Remember to double back on the wire going into the ring terminal.
6. EGT, large span. Normally aspirated (carburetor) engines at normal cruise display a “DIFF” of 125 to 175
o
F
spread between cylinders. Injected engines at normal cruise display a “DIFF” 50 to 90
o
F spread between
cylinders. All cylinders are measured by a common circuitry. It is almost impossible not to have identical calibration
on all channels.
7. If the temperature reading is changing more than 500°F in one second it should be questioned and a loose wire
crimp or probe should be suspected. A malfunctioning probe will automatically be removed from the scan.
8. All EGT or CHT readings seem to high or low or unsteady. Use a DVM (digital voltmeter) to measure the difference
between 950 ground and the engine block ground. If the difference is greater than 0.5 volts with the alternator
charging. Then remove the EDM-960 ground (Black wire) from the instrument panel and connect it directly to the
ENGINE BLOCK for GROUND.
9. OAT readings off by 25 degrees, but oil and CHT readings OK, look for copper wire spliced in line to OAT probe.
OAT reading can be fine tuned +/- 5 degrees, see reset procedure. Engine heat could also be the cause.
10. The instrument configures itself automatically for 14 or 28 volt electrical systems.