CHT EGT lost on 1 and 2 - 500hr exhaust replacement

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SteveHarding
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CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by SteveHarding »

Thoughts on zero reading on Vm1000 for CHT & EGT on Cyl 1 and 2 during normal flight. VH - ZLY is currently in for annual at the moment and trying to diagnose this issue. Readings on cyl 2 returned on short flight to workshop however 1 is still down. Also thoughts on 500 hour exhaust replacement . Seems to be a 4 month wait on parts at the moment.

GimpyPilot
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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by GimpyPilot »

Is your engine running normally in spite of the indications? Are there any indications on the HSA? Do you have access to diagnostic (PowerLink) software and cable? I would run a Phase I diagnostic sequence first. If that's normal, then you likely have a sensor or wiring issue, which you can resolve with help from JPI. If you've got abnormal diagnostic results, I would look to fuel injectors first.

The exhaust is made by Dawley. They should be able to fix you up with whatever you need.

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by Bigphoto »

I sent in my exhaust to Dawley and they turned it in 2 weeks. Had issue with CHT/EGT on number 2 and turned out to be a bad fuel injector that I replace.

SteveHarding
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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by SteveHarding »

Thankyou Gimpy and bigphoto - ZLY still in the workshop waiting replacement pins. Still haven't diagnosed CHT and EGT as yet after LAME has sent an email to Continental. I've mentioned the fuel injector comments you have made and will post more info once he has emailed me the diagnostics report.
He seemed to think it might be an issue of voltage to sensors out of the FADEC. ??

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by tafisama »

I would lean more on bad sensors.If the Fadec lights on the HSI are not on and the engine is running smooth then the sensor is either grounded or open.Is this only happening in flight?

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by SteveHarding »

Yes only in flight and cyl 2 can return. No fadec warning lights and yes engine running smooth on ground and in flight

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by N645XL »

Look for wire harness chaffing too.

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by SteveHarding »

So update from TCM with emaill to the LAME recommending ECU 1 be replaced. The data from the download shows voltage not present on volt 1 and volt 2 and then returns on volt 2 and 2CHT and 2EGT also return. Volt 1 stays at zero and no CHT or EGT present. TCM quick to advise an expensive replacement of ECU 1. Price to be confirmed.
Based upon checking harness chaffing and sensors is this voltage reading a return voltage from the sensors or an output voltage?Thoughts greatly appreciated.
Data file attached
Attachments
VH-ZLY 2020 Fadec.csv
(130.32 KiB) Downloaded 59 times

tafisama
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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by tafisama »

This is not good,having to replace the ecu because its not supplying voltage to sensors.

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Re: CHT EGT lost on 1 and 2 - 500hr exhaust replacement

Post by N645XL »

SteveHarding - First I'm sorry you have this problem. Very frustrating indeed. I'd already typed out long-winded thoughts on general trouble-shooting steps that served me well during my long-lost avionics tech days but, alas, my response vanished so I'll try to recreate it. For your consideration and not necessarily in a practical order based on your resources:
1. Substitution of known good components such as the ECU, wire harness, and sensors.
2. Inspection of components for continuity and/or high impedance shorts using a basic ohm meter and megger.
3. Inspection of connector pins to ensure they're seated and making good contact and there is no contamination in the housing backs.
4. Inspect solder connections to ensure they're not cold joints that have lost continuity. (Rare but I've seen it twice where reheating years old solder fixed the issue.)
5. Ground connections have a tendency to oxidize and kill a circuit. I'd loosen the bolts and ensure the grounds are clean.

As you're evaluating your options think 3D. On the ground you don't necessarily have the vibration and heat you do in-flight from the rushing air and cylinder/exhaust heat. Considering this has both an intermittent and continuous failure condition my thoughts go to the harness where both circuits travel a common path. I'd check clamps and other areas where the wires could be chaffing but especially. Where the wire bundle is very close to an adjacent object. Look good! I've seen nearly microscopic insulation nicks where it appeared a thin layer of insulation was still covering the wire but there was just enough continuity to ground to kill the circuit. Two incidents come to mind which baffled more than a few techs trouble-shooting the problem.

Regarding your question related to sensor voltage (my GUESS and that's all it is) is the sensors are analog and either their resistance or capacitance changes with the environment they're monitoring. In other words, there is a current passing through the sensor which varies with the resistance (for example). Based on the current-reading in that circuit the value in your spreadsheet is derived.

My gut tells me the ECU is likely fine (again this is my gut feeling). I also suspect the sensors are fine (I'm assuming both abnormal readings happened simultaneously). If you weren't hit by lightning I doubt they failed simultaneously. As stated twice previously, if it were me I'd focus on the wire harness and especially any common connector both circuits share. I could never prove it but I think more than a couple of the harness issues experienced in this aircraft are caused by oil changes done in a manner which allowed oil to run into the connector backs contaminating the connections. You may want to open the clamps and spray an electrical cleaner in there to ensure there are no high (or low) impedance shorts at the pins.

I wish I could do more but we're about 8,800 NM distant. Good luck and keep us posted on the resolution.

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