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EGT and TIT

Screw-in TIT probe?

JPI now has a screw-in type TIT probe – P/n 1020062 – Size: 7/16″.

If you need a different size, please go to Alcor’s web site at:

http://www.alcorinc.com/sensors/category-02.php

How far must the EGT probes be mounted from the cylinder head?

2 to 4 inches are recommended. Closer will shorten the life of the probes. Farther from cylinder head – up to 53/4″ – from exhaust stack flange is okay. Uniform spacing is important. Temperature differences of 100 degrees per inch can be expected.

EGT clamps are too short. Not enough thread slots.

We have larger clamps available. Call JPI 800-345-4574

EGT probe slips out of mounting.

Remove and squeeze the thimble and reassemble.

TIT probe pin assignments for EDM-700/800.

EDM-700/800 Pin assignments on the P1 connector:
yel 1, red 2, OIL
yel 3, red 4, IND
yel 5, red 6, CARB (or CDT)
yel 14, red 15, OAT
yel 16, red 17, TIT
yel 18, red 19, TIT-2 (2nd TIT)
gry 12, Remote alarm (Sinks to ground)
red 13, + Power
wht 24 , RS-232 data port
blk 25, Engine ground.   ** ( Pin # 11 not used.)

When power is reduced, EGTs increase to 1500.

This is normal. Due to unburned fuel air continuing combustion in exhaust manifold

Can existing TIT probe be used?

Yes, IF the aircrafts TIT probe is the same type thermocouple. ( Type K red and yellow wire.) Just parallel the conection. Connect red to red and yellow to yellow. See the EDM-700/800 Installation manual Report #103 under “Turbine Inlet Temperature Probe (TIT)”, or Installation Manual Report # 760 under “Turbine Inlet Temperature Probe (TIT)” for the EDM-760.

Calibration procedure:

1. Go to pilot program mode (Hold both buttons to see PROGRAM).
2.Tap STEP until you see RATE.
3. Hold both buttons until you see ORIGT-N.  ( ‘ORIG TIT?N’ for the 760)
4. Tap LF to change to ORIGT-Y. Now tap ‘Step’.
5. See CAL TIT then ‘TIT+0’.     ( ‘TIT ADJ + 0’ for the 760 )
6. Tap or hold LF to change the correction factor (Ex: if the EDM reads 100 less than the aircraft’s TIT, set the display to read TIT+100)
7. Tap STEP to exit.

EGT bars go off scale high or low

  • The EDM might be in the Normalize view. Switch to Percentage view: hold LF button for three seconds.
  • Might be in Celsius units but the alarm limits are still set for Fahrenheit.
  • Check that if a bayonet or threaded adapter probe is installed, that it is screwed in tightly and the threads are clean in order to ground the factory probe. If adapter is not grounded well to engine, voltage will be applied to the adapter thermocouple junction and disrupt the EDM instrument.

EGT probes with heat sink fins: what should I replace it with?

May be an ungrounded probe, only replace with an ungrounded probe

How far must the EGT probes be mounted from the exhaust flange?

2 to 4 inches are recommended. Closer will shorten the life of the probes – flame-front is at 1.5″. Farther cylinder head? (Up to 6 inches) is okay. Uniform spacing is important. Temperature differences of 100 degrees per inch can be expected.

DIF reading is too high.

Up to 150 degrees DIF is okay.

Bar graphs are too low (only a few segments).

  • Unit starts reading at 825F.
  • Or the unit may be set to Celsius without changing the red line limits (set TIT for EGT limits). Set TIT limit to about 900 degrees C. When changing to Celsius all alarm must be reset to Celsius limits.

Blank EGT column – digital reading OK

Check EGT digital reading on that particular cylinder. If lower than 825 degrees bar graph will not show. If 800 or lower, check probe and connections.

Blank EGT column and digits.

Check at ambient. Check as temperature rises to see where probe fails. Three causes for removal from scan are:

  • Open probe – shows error
  • Low probe reading when EGTs>1000 degrees – digital should read
  • Rapid fluctuations in temp reading on that probe.

EGTs & CHTs are reading about half of what they should be

Probably are set to Celsius. Reprogram to Fahrenheit. See Pilot’s Guide for programming information.

EGT & CHT read 300F too high

Check that if a bayonet or threaded adapter probe is installed, that it is screwed in tightly and the threads are clean in order to ground the factory probe. If adapter is not grounded well to engine, voltage will be applied to the adapter thermocouple junction and disrupt the EDM instrument.

•  Check that the EDM is grounded at the engine case(not in the instrument panel). Do not use panel ground, battery ground, or airframe ground. Airframe ground can vary from engine ground by 1/4v. This could cause the EDM to show too ‘High’ or ‘Low’,  EGT, CHT temps. Or show ‘Unsteady’ readings. If grounded to the panel, to check if this ground is OK, use a digital voltmeter to measure the difference between the EDM ground and the engine block ground. If the difference is greater than 0.5 volts with the alternator charging, then remove the EDM ground (black wire) from instrument panel and connect it directly to the engine block ground.

EGT reading jumps up and down on one probe only

• Swap the ‘faulty’ EGT probes wire to the next cylinders ‘good’ probe.  Now since that ‘good’ probes wire is now off, fasten it to the ‘faulty’ probe. You just swap the wire, not the probes. Now turn on the EDM. Does the other ‘good’ EDM cylinder channel now behave in the same way – jumps up and down..?  Then it’s the probe. If not and the original ‘faulty’ cylinder is still behaving in the same way, (no change)-  then it could be a bad crimp or connection or instrument is bad.

• Check for a bent or recessed pin on the rear P2 EDM-700/800 connector. (P1 & P2 for the 760)

• Check crimps between probe and harness.

•  Check that the EDM is grounded at the engine case(not in the instrument panel). Do not use panel ground, battery ground, or airframe ground. Airframe ground can vary from engine ground by 1/4v. This could cause the EDM to show too ‘High’ or ‘Low’,  EGT, CHT temps. Or show ‘Unsteady’ readings. If grounded to the panel, to check if this ground is OK, use a digital voltmeter to measure the difference between the EDM ground and the engine block ground. If the difference is greater than 0.5 volts with the alternator charging, then remove the EDM ground (black wire) from instrument panel and connect it directly to the engine block ground.

• Check that leads are not shorted together on the harness or where the probes connect to the harness.

• Check if the probe may have been mounted in a slip joint. Probes are not under warranty when mounted on a slip joint.

EGT reads low and CHT reads high

Check if the EGT and CHT probe leads are reversed.

EGT too high

Probes should be 2-4″ from exhaust flange.

 

EGTs not uniform, especially during low power operation

This is normal. Fuel and air distribution is not optimal at low power settings.

Older EDM with erratic CHT & EGT readings

Loose connections at the eye terminal – tighten or replace terminals.

EGTs rise during single magneto check

This is normal due to incomplete combustion causing the flame head to persist longer.

High, jumpy, or missing readings.

Make sure that the unit is grounded at the engine. If voltage difference is greater than 0.5 volts with the alternator charging then move ground to engine block.

Low EGT & high EGT DIF reading with no CHT reading.

EGT & CHT probe leads swapped. CHT too high to register.

Missing one column, but column okay during self test at start up.

Check CHT on that cylinder to see if may be bad cylinder. If the CHT is okay then proceed, otherwise the cylinder is likely bad.

•  Swap the ‘faulty’ probes wire to the next cylinders ‘good’ probe.  Now since that ‘good’ probes wire is now off, fasten it to the ‘faulty’ probe. You just swap the wire, not the probes. Now turn on the EDM and get up to operating temperature. Does the other ‘good’ EDM cylinder channel now behave in the same way – missing bar column?  Then it’s the probe. If not and the original ‘faulty’ cylinder is still behaving in the same way, (no change)-  then it could be a bad crimp or connection or instrument is bad.

• Check for a bent or recessed pin on the rear P2 connector.

• Check crimps between probe and harness on that particular EGT channel.

• Check that leads are not shorted together on the harness or where the probes connect to the harness.

Temperatures off by 25 degrees

Check for copper wire substituted for thermocouple wire

Temps jump more than 500F in one second.

Reading should not be trusted. Check for loose wire crimp or bad probe.

Negative temperature reading.

Adapter probe not grounded or probe leads reversed.

How to change EGT display resolution from 10 degrees to 1 degrees?

  • Go to pilot program mode (Hold both buttons to see PROGRAM).
  • Tap STEP until you see EGT 1? N.
  • Tap LF to change to EGT 1? Y.
  • Tap STEP repeatedly to END Y.

How to mount EGT probes?

Keep the distance from the cylinder head the same for each probe. 2 to 4 inches is recommended. Closer will shorten the life of the probes. Farther (up to 5 3/4″ inches) is okay. Uniform spacing is important. Temperature differences of 100° per inch can be expected.

Do not mount probe in a slip-joint. If you must mount in a slip joint, drill the inner stack hole oversize(3/8″) so that vibration won’t shear the probe. Outer stack hole: 1/8″. Probes sheared by slip-joints are NOT covered by waranty.

TIT Calibration.

To calibrate the EDM-700/800/760 using the ‘factory’ TIT probe.

Parallel the conection. K type thermocouple – connect red to red and yellow to yellow. See your EDM-700/800 Install Manual Rpt #103 for documentation supporting this, or your Pilot’s Guide. Also Rpt # 760 for the EDM-760, or its Pilot’s Guide.

To calibrate the EDM:
1. Go to pilot program mode (Hold both buttons to see PROGRAM).
2.Tap STEP until you see RATE.
3. Hold both buttons until you see ORIG TIT … ORIGT-N.
4. Tap LF to change to ORIGT-Y.
5. See CAL TIT … TIT+0.
6. Tap or hold LF to change the correction factor (for example, if the EDM reads 100 less than the aircraft’s TIT, set the display to read TIT+100)
7. Tap STEP to exit.