Hello, I have a newly assembled Wren 54 MK3 auto start that refuses to run. It starts up on power Max or propane, goes up to about 20,000 rpm, then shuts down. Other times it goes up past 30,000 rpm, starts to ramp up then shuts down. When it does this, I get funny RPM readings, sometimes 16,000 rpm then 30,000 rpm and within one second, it goes up to 160,000 rpm then it shuts down. I know that it is not running hot because it is no where near the 800 degree cut off.

When this happens the date terminal indicates either rpm low or flame out.

My friends tried to talk me into buying a P60 or a super Bee, but I told them that I think that the Wren 54 was a superior engine and now I'm eating crow. PLEASE HELP! Your input and feedback is appreciated. Thank you.

MARK.

What are you using to power the ECU/engine (Mah & Voltage)? What type of battery?

Could it be a battery power issue?

Please check and make SURE that your propane and fuel lines are not reversed. Seperate your RPM sensor wires from the starter wires also. Scott

Make also sure your compressor wheel is not rubbing on its housing.

The main reason for crazy rpm readings is the glow plug and starter motor wires. They have to be braided together and as far away as possible from the rpm sensor.

Chris

Yes, twist the glow plug cables, should take care of leakage to the RPM sensor, the crazy readings must be what is causing it to shut down

Twist your glow plug leads around each other.... (that is one of the causes of funny RPM readings...confuses the ECU and it shuts down..)

Make sure your pump is primed and there is fuel in the line all the way to the engine

And as mentioned above, make sure you do not have your gas and fuel lines mixed up.

The 54 is a wonderful engine! you won't be sorry.......

I'll trade you my GREAT (no kidding) running P60 for your Wren

........I'll second what This character has to say...

Brg

Dave

I had exactly the same thing about 2 months ago..... Have you lengthened any wires.... I had to, to get it in the plane and it turned out to be a simple answer....... I had lengthened the two (Both Black) glow plug wires and when I soldered in the extra lengths I had crossed the wires over which I didnt think would matter as both were black and are only glow wires after all !. There must be some sort of common negative though because when I swapped them back all worked well. I had also plugged the temp sensor in the wrong way round at the ECU Which didn't help............

This is a lovely engine and I am sure this might be your problem..... Keeping the Glow wires away from the RPM Sensor is also important

Dennis

www.densplanes.co.uk

Mark,

We think it sounds like a wiring problem, but if you are sure you've got everything plugged in right and that the glowplug wires are twisted together, then there may be a problem with the ECU. Please PM me with a phone number and a time when you can be reached, and I'll get one of the guys to talk to you. If the ECU is faulty we can replace it.


Sara Parish
Wren Turbines

Mark,
Wren makes a great motor and their service is 1st class.

We've spoken to Mark on the phone. It's a very unusual fault, we haven't come across one quite like it before, so a replacement ECU and rpm pickup are on their way to him now.

Sara Parish
Wren Turbines

I would like to thank everyone for the helpful input. It seems that the problem may be with the ECU or the RPM pickup. Thank you Sara and "The Rest of the Wren Team" for the very quick response and help. I hope that i can get this engine to run after i get back from vacation. I would also like to thank Peter from Altecare; his service and prices are fantastic.

-Mark

Mark

I have seen the same thing happen on a few engines and the last one only a couple of weeks ago and if the cause is the same then it is simply fixed.

Can you flick the turbine wheel and have a look what the lowest RPM reading you can get? It should read right down to 200rpm. If it does not then you may need to take the FOD guard off and simply rub a magnet around the inlet area. You should then find it does read down to 200. I can't tell why this works but it just does. My guess is the engine will run once thats done.

Jason

Jason, that is very interesting. My lowest RPM reading was about 16,000 RPM. I will try your suggestion. Thanks. Mark

Mark

I had a similiar problem with my Wren 44. It would cut out when inverted and I could not figure out why. The answer was the rpm pickup magnet had become demagnetised and would not read below 800rpm. Following Wren's instructions I passed a magnet over the intake several times and this cured the problem. I know it sounds more like magic than engineering but it did the trick!

John

what you also can do is make a vertical movement over the rpm sensor with a strong neodym magnet from front to back.
it will make it more sensitive..
that is what you basicly are doing jason.
most faults are:

tied the rpm sensor to the starter and glow plug cable.
both or one plug and starter cables are not twisted.
low voltage on the RX input of the receiver.
cables made longer (basicly making them a large arial).
connected the ground from the glowplug to far from the plug.
Digital Servo,s running not neutral (loaded) or to close to ecu causing a distorted signal on the signal bus.

temp problems:

when starting temp goes to 0 causing a bad start after 10 seconds
temp cable reversed

constant reading 64000 rpm even in stop mode (1 khz signal caused by sensor picking up noice) use the solutions above)

when in start reading weird rpm signals :
Glowplug coils is shortcutting causing drainage of lots of amps
Glowplug is to cold type (i always used on all wrens O.S 3)( for merlin i use O.S FS type plug)
these things might sound weird but they can cause these things)
also none twisted cables or rpm cable is tied down to other cables cause these

no rpm reading :

cable reversed

neodym magnet demagnitised due to heat (hot start or small fire )
if the temp goes over 150 degrees celcius on the spinner it will lose its magnetic strength
only solution is to exchange the spinner(magnet) at this time.
NO MAGNET in spinner (added 28-01-2008)


turbine shuts down or flames out over about 100000 rpm,s
rpm sensor mounted wrong or fell off causing the mag signal to cross the sensor vertical (if the sensor is 90 degrees opposite from magnet)
losing pulses if going to fast..
Magnet demagnitised due to heat


these are most problem(s) known to me , when people came with problems to us..

this is a good checklist in case of problems
those are my 2 eurocents anyway...[:-]

Lots of VERY good information there Sandor. THanks for posting it. I have run acorss many of those in the years, but forgot some of them. Will save that as a help file. Scott
PS The magnet trick was a must remember for the RAMS-seams like they needed it alot. Scott

"I'll get by with a little help from my friends".... and there are a lot of them out there. Thanks, everyone!

Sara Parish
Wren Turbines

hey mark try holding the picthure of that realy ugly girl i sent you in front of the turbine if it dont run then youre pretty much done
lol

just kidding try using a magnet rubbing over the front of the turbines intake

Problem solved!

All those who thought it was something to do with the magnet .... you were on the right track.

There was no magnet in the compressor nut. We know what happened, a few weeks ago some compressor nuts which hadn't yet had magnets fitted got mixed up with a batch of nuts that already had magnets. We thought we'd sorted them all out but one got away! With ready-built engines the fault would have shown up and been corrected here, but since Mark bought a kit it wasn't apparent.

Thanks for your patience, Mark, replacement nut is in the post.

Sara Parish
Wren Turbines

I finally had some time to install the new compressor nut.All I can say is "outstanding"!!! The engine starts up smoothly,runs great and the throttle response is very,very fast.Great job WREN, you have a life long customer.
Sara, please let me know where you would like me to send the ECU, and thank you and every one at WREN for all the help. Mark Cunningham.

It's an amazing little engine, isn't it?? Mine has been totally reliable, just fire and fly.......

As always great support and excellent service[8D]

Paul