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EGT faulty

Old 05-19-2006, 05:01 PM
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Default EGT faulty

I have just got the engine back from a service and upgrade to R spec by the PST factory in Thailand, and the egt is faulty. It is saying egt is 979 degrees C. If I wiggle the yellow cable near to the point where it goes into the engine connector to the wire probe, it sometimes changes to show room temperature. If I wiggle it again it changes back to 979 degrees. The yellow cable has no signs of stress or damage whatsoever. What has gone wrong and how is it mended?

Harry
Old 05-19-2006, 05:44 PM
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Default RE: EGT faulty

The 979 C is an indication of an open circuit.

Just to confirm, you're wiggling it close to the little blade connector, or close to the base where it converts to the 1/16th" inconel probe? If the brake is it close to the base, the first solution is to contact your rep or the PST factory and request a new probe. Alternately, if its out of warrantee and you know of a local manufacturer / supplier of thermocouples, you can purchase a K-type, 1/16" diameter, but please not that it must be a non-grounded style probe. By that, I mean neither of the probe wires is internally shorted to the inconel housing.

Kelly
Old 05-20-2006, 03:39 AM
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Default RE: EGT faulty

It's close to the base. The break must be in the wire or inside the base itself.

Is there a reason for the large yellow connectors used on the egt wiring? Space is a bit of a problem in my model, is there any reason why I shouldn't change the yellow connector for a normal Futaba/JR servo plug and socket?

Harry
Old 05-20-2006, 11:00 AM
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Default RE: EGT faulty

Its purely an issue to do with international standards for thermocouple connectors. K-type thermocouples typically come with a connector like that, or a larger form.

See here for example: [link=http://www.omega.com/toc_asp/subsectionSC.asp?subsection=G03&book=Temperature]Omega Thermocouple Link[/link]

Gaspar's Fadec uses a thermocouple with a JR style connector, so its definitely possible. Of coarse, the user accepts responsibility for any modifications to the hardware that PST supplies, and problems that may result. There's no reason it couldn't work so long as its done right though.

Kelly
Old 05-20-2006, 02:21 PM
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Default RE: EGT faulty

Thanks Kelly. I have googled about thermocouples and get the feeling that to change the plug would not be a good idea so I will stick with the existing coupler.

H
Old 11-25-2006, 02:14 PM
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Default RE: EGT faulty

I think I have the same problem. Mine also says 979 degrees c. I bought this turbine from someone and he said he had to send it in the the manufacture to get the egt replaced and he has NOT started it since he got it back. (He just shipped it to me) He said the turbine has had 59 starts. When they fix the turbine at the factory, do they run it before they ship it back to the customer? When I start mine I cannot get it above 6000 RPM. I know the glow is lighting. It says it and I hear it. Its like the motor needs to spin the turbine way up to 30,00rpm but it just shuts off after 6000 rpm then turns back on after 1-2 seconds and spins it back up to 6000 rpm and then shuts off after 4 trys. The GDT says START FAIL..
thanks,Mario
Old 11-25-2006, 06:40 PM
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Default RE: EGT faulty

Hi Mario,

By your description, I believe your ECU is acting exactly as it should.

The ECU only pulses the starter motor initially, waiting to see an increase in temperature. When it sees a rise in EGT, it will only then apply full voltage to the starter motor and try to achieve higher that 6-7K. While its winding up, it watches to see if the EGT passes 110C, and if the RPM is increasing. Once it sees 110C, the fuel pump is activated and the engine should then increase in RPM, eventually calibrating the idle speed and giving you control.

If the propane doesn't ignite and generate enough heat, your engine may never pass the pulsing stage, and it will not start.
If it passes the pulsing stage and never sees 110C in the ramp sequence, it will not start....
It it initially lights off, and rises in EGT but then falls without achieving 110C, its a propane pressure problem. Try feeding the system directly from your off-board bottle (powermax must be held up side down if feeding directly, ensure that no liquid start fuel enters the enigne)

I'd have a close look at your setup....
1st, please have a read of the manual. All of what I've stated here is in the manual, around page 20...
([link=http://www.pstjets.com/download/J600R%20Manual%20V1.5.3.1%20public.pdf]link to J600R manual[/link])
2nd, please check the glow plug to see that the element is exposed enough, although you sound pretty confident that its' igniting...
3rd, please check that you're start fuel solenoid is functioning (the red LED is on when gas should be flowing) and the line is not partially blocked. You may even want to do a start with the start fuel line disconnected from the engine. The engine of coarse won't start, but you can at least verify that there is flow by feeling the outlet of the disconnected line.


Lastly,
I'm a little confused about your EGT reading, since a reading of 979C (a sure sign of a broken thermocouple circuit) will be outside of the EGT's safe range and the ECU will not allow you to activate the start sequence... Do I take this to mean that you've already changed the thermocouple and rectified that problem?

If you're still stuck, you're more than welcome to sent it up to me for a checkup.

Kelly
Old 11-25-2006, 09:49 PM
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Default RE: EGT faulty

Mine had the same problem, about a year ago, and it was definitely the Thermocouple (as diagnosed by Kelly W). I ordered a new one from Dreamworks RC and it has been flawless ever since. Kelly is the Man!
Old 11-25-2006, 09:58 PM
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Default RE: EGT faulty

Thanks so very much Kelly! It was the thermocoupler circuit. The GDT did read 979 c degrees when I switched it on. When I kept jiggling around the temp sensor and it was jummping to the outside temp then back up to 979 degrees c. It, (the temp sensor) read on the GDT what it was outside. I think about 35-40 degrees c. Then I finally got it to stay at that temp. (I had to open the EDT circuit and tighten down the screws) And now it starts fine! Reading temp on the EGT goea up when the turbine is up and running, and goes down when the turbine is shutdown and in cool down mode.
Thanks,Mario
Old 11-26-2006, 11:54 AM
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Default RE: EGT faulty

Thanks guys,

FYI, my response above is usually the case for problems like what you've described, normally a propane / butane issue... The failure mode of a thermocouple will often be an outright broken circuit, in which case it'll read 979 or 980 Celsius. The reasoning behind this is that the thermocouple operates by producing an extremely small voltage in relation to the temperature its seeing. That signal is heavily amplified before being converted into a digital value that the ECU displays as EGT. When the circuit is broken, the amplifier saturates and the result is understood by the ECU as 979C. I have yet to see (and don't expect to ever see) an engine with a shut down data readout with 979C, since under normal operation the ECU will attempt to hold back once it sees 760C, and it'll give up and shut down at 800C.

A failed thermocouple which still randomly makes contact can cause any number of failure modes, but the diagnosis always involves looking for wild temperature fluctuations while jiggling the cable. The good part is that a 979 reading will instantly shut down the motor and very likely keep you from achieving a start.

Anyhow, I'm glad you seem to have it under control. As I've mentioned earlier, if you're purchasing a replacement thermocouple make sure its an 'ungrounded' type. Using a grounded thermocouple can produce a ground loop through the other connections to the engine, and the ECU will not function properly. A grounded sensor will often display artificially high reeadings as well, the extent of which change in relation to that other circuits are in operation.

Kelly
Old 12-09-2006, 04:08 PM
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Default RE: EGT faulty

Hello Kelly, I need to order a new thermocoupler from Dream works. It's reading 979 C Do you have a link to the one I need to order?
Thanks,
Mario
I have a PST J600R
Is it the standard K type? thermo.
Old 12-10-2006, 02:14 PM
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Default RE: EGT faulty

ORIGINAL: Moe142

Hello Kelly, I need to order a new thermocoupler from Dream works. It's reading 979 C Do you have a link to the one I need to order?
Thanks,
Mario
I have a PST J600R
Is it the standard K type? thermo.
Yes, its a K-type and any thermocouple should work, so long as its ungrounded. Nothing against Dreamworks, but if you order a thermocouple through Dean W at PSTNA, it'll be a probe that is specified on the engine. I can't verify that an alternate supplier's probes are ungrounded, nor can I predict how tight the fit will be in the mounting bracket. Another probe may have a different length, and the mount that's supplied with the motor may not fit as its meant to. I'd suggest calling Dean through the contact info [link=http://www.pstna.com/contact.htm]here[/link].

Kelly
Old 12-10-2006, 04:16 PM
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Default RE: EGT faulty

Thanks Kelly! I just e-mailed Dean at PSTNA. If they do have the thermocouple in stock I want to oder one and have it shipped tomorrow (mon Dec 11th if possible)
Thanks,Mario
Old 12-10-2006, 04:50 PM
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Default RE: EGT faulty

Hi Guys.
I have also had the 979 readout from a faulty thermocouple. I originally had two Pst 600 's and had to return one to Thailand for a compressor replacement. Don't ask me how I damaged it, I don't know because I always use FOD guards. PST upgraded the motor to a 600R and now my problems have started. The 600 runs like a watch and gives no hassles. The 600R is difficult to start. It will get to 30000rpm, (starter drop out speed) and then will not pick up to idle. Sometimes it will get to idle but if I do a slam check the flame will exit the tailpipe like a blowlamp. I've had it on the testbench for ages. The controller says I have had 60 starts since receiving it back and total running time is 1hr 42 mins none of which have been airborne time. I have tried just about every ramp time settings. The TEMS controller is good and I have spoken to the manufactureres and we are running out of ideas. We do fly at 5500 feet above sea level. Does anyone else run a 600R at high altitudes sucessfully? My motor is on its way back to PST for the third time
Regards
Dave Armitage
Old 12-11-2006, 11:31 AM
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Default RE: EGT faulty

[sm=75_75.gif] Faulty EGT probe will show 979 C. However, symptoms described by Dave is not related to faulty EGT probe and the engine will be looked at again. The problem here is quite unique and you can be assured that we will take care of the engine to our full service ability.

Regards,
Kraivuth S.
PST Jets Thailand

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