Rotax 914 Turbo - TCU light Blinking

Hello Guys,

Here is my problen with my ROTAX 914 Turbo

Last weekend, when I was going to take off in my Magni Gyro, I advance the throttle to full and then advance the lever to engage the turbo, I fill when the turbo kick in for a few seconds but then then I fill the engine loose power like if I move the lever back to disengage the turbo. I abort the take off and get back to the hangar. Thinking that the problem was old fuel, I remove completely the fuel, put new fuel, new plugs, clean the air filter, clean carburators, start the engine and everything was OK. Since is was late, I dont fly it.

Today I start my engine ROTAX 914 Turbo and during the warn up, around 3 minutes of engine runing at 2,000 RPM, the Ambar Warning TCU light, blink 3 times and then stop blinking.

The Engine is installed on a Magni Gyro and it has 248hrs

This was my EIS reading when this happened:

Fuel Presure: 6.5psi
Engine RPM: 2,000
Oil Temp: 95�
EGT: 1,000
CHT: 120

I was checking the Rotax 914 Trouble Shoting Manual and its says that if this Ambar TCU warning light blink, its mean that there can be a problem in:

Wiring Sensor
Sensor damage
TCU Failure
Air Box Leakage


So where you recomend me to start looking for the problem?

THX

Isaac

I'm no 914 expert, but I doubt it would be wiring, for the fault would immediately appear if it was. A wire is either broken, or not. If the problem appears everytime under exact same setting, it's most probably not an intermittent wiring problem.

Get the easiest to solve suggested problem out of the way, check the airbox, if any leaks appeared.

The first issue you had, with loss of power, makes it sound like a sensor or TCU problem.

Check the connection to the sensors, maybe the plug is loose, causing an intermittent fault with engine vibration.

If not that, you would have to seek professional diagnostic tools, to check the sensor or TCU. If you had a friends unit to swop out, this way you could eliminate these components from your search.

It sounds like the turbo wastegate may be sticking.

Good luck it could be one of 100 things, the 914 is a night mare to work out problems on, and to make it worse, there is no way of plugging into the "computer" (what a joke that is) to see what caused the fault.
I now have 2 machines in the hangar with 914's, none of them are operator friendly when you get a fault.

How ever if it started blinking and stopped, there is no problem, its only a problem if it keeps blinking. even worse when the red one starts

Only time i had my red one blink was wen i saw 9000rpm onit.

Turbo_Boss said:

I was checking the Rotax 914 Trouble Shoting Manual and its says that if this Ambar TCU warning light blink, its mean that there can be a problem in:

Wiring Sensor
Sensor damage
TCU Failure
Air Box Leakage

Click to expand...

I have neve worked on a turbo 914 but the information given above makes it appear that the problem is low Manifold Air Pressure (MAP).

Based on that and the sudden drop in rpm I would be looking for a manifold air leak to start with.

If that is OK look at the exhaust system for leaks.

We have had chaffed wires on FADEC control systems and they can give all kinds of spurious warnings and strange operation without recording a fault so inspect all the wiring for and chaffing.

It could be a sensor or a TCU failure but I guess you have no way of testing them so swopping them out with another one would be the way to go.

Do the easy stuff first, leaks are more likley to be the cause and of course quicker and cheaper to fix.

Let us know how it goes.

I am very familiar with turbochargers, the loss of power after feeling the turbo kick in is not uncommon if the servo fails that controls the wastegate, as the turbo is effectively not regulated at that point it "bogs down" due to the wastegate not closing to increase flow through the turbo. On the 914 the system lacks sophistication and while this makes it easy to view certain things like making sure the wastegate lever operates, I think it makes it prone to issues, any issues however are usually easy and cost effective fixes, one way to check the servo is to move the wastegate lever then turn on the ignition system to see if the servo resets, if so the odds are that this is not the issue, the good thing about this issue is that if it is so then the turbo itself will not be damaged and you can do the check before having to remove anything.

I believe Buck has suggested a likely suspect and it would be wise to check the waste gate.

They get very, very hot and often stick on FW aircraft. We can tell because there is a drop in manifold pressure = it won't maintain pressure at altitude.

We often fix them by just rapping on it with a small tool or rock. It works almost every time.

On type certificated aircraft it would be recommended to lubricate the waste gate shaft with mouse milk each oil change. These is often miised and yes this a real product.

http://www.mousemilk.com/

Turbo,
One other thing that had me stumped for ages, check and i mean really check, the little black pressure lines between the carbs and air box, and air box and fuel pressure valve, i had a hole under the protective wrapping, it was upsetting the pressures and the motor was not happy, wouldnt run over 4k, so i would recomend unwrapping these lines and check for holes.