MCX 180 Over Boosting

[SNAFU]

My MCX 180 has always run about 9 psi boost at 6500'. This weekend the thing was a rocket and I was shocked when the boost gauge read 14 psi. I babied the thing for the rest of the day and checked things out when I got home.

The waste gate moved freely and compressed air will move the actuator so that part is working fine. I think the problem may be the TCV valve. With no power on the valve, air can flow through the valve and out the waste gate port. However, air also flows out the bleed port.

When I add a 12v source, the valve closes and boost pressure can no longer pass through. The connection between the waste gate port and bleed port are open which I think is correct. This would allow pressure in the actuator to bleed off through this port and the waste gate can close.

I think there must be something wrong with the valve that is allowing air to pass though the bleed port and waste gate port at the same time. I don't know how this valve is configured, but it may have been damaged and is not closing the bleed port when it should. This could cause higher than expected boost levels. I may be out to lunch here, but this is all I can come up with so far.

Any thoughts?

 

[M5-]

You are probably on the right track, thats about all I can think of off the top of my head. Check the wiring on that from the front of the sled, my Nytro wore through, actually melted it on a huge snow day in December. Pretty sure Trent has those in stock, if not I may know of one.

M5

 

[SNAFU]

Thanks for the reply. I checked wire continuity from the MCX box to the valve and it checks out. However, with the sled running at an idle, the voltage at the valve is about 7.6 V and the valve is open allowing boost pressure to the waste gate.

I think this valve should pulse open and closed to control waste gate operation and boost according to the map based on baro pressure, rpm, throttle position, etc. Maybe 7.6V is the low part of the pulse signal and 12V is the high that closes the valve.

Are running the TCV valve or a manual boost controller?

 

[SNAFU]

Maybe someone can answer this question. Is the TCV solenoid supposed energize (close) as soon as the engine is started?

 

[SNAFU]

So, it turns out my TCV was damaged and I ended up replacing it. I like how the system works and controls boost based on elevation so replaced the valve instead of installing a manual boost controller.

For those that are interested, this is how I believe the TCV works. When you start your sled, the TCV solenoid will be de-energized, or open. This will allow boost pressure to pass from the turbo to the wastegate. The bleed port on the solenoid will be closed. The is the port that is open to atmosphere. Your wastegate actuator should be set up for your base boost at sea level. In my case this is 6 psi. The TCV will stay open until it is commanded to close. At some pressure, maybe at or below your base boost pressure setting, the MCX IIC controller will send a 12V signal to the TCV and it will close. There is no longer pressure to the wastegate so it cannot open. The map in your MCX controller will determine the correct boost pressure based on elevation. For example, at 6500 feet boost pressure should be about 9-10 psi. When this pressure is reached, the MCX controller will open the TCV allowing pressure to the wastegate. Since 9 psi is greater than the 6 psi spring setting in the wastegate, it will open. When the wastegate opens, the boost pressure will drop below the desired value, and the TCV will close again. The opening and closing of the valve can occur many times per second. Only when the TCV is closed will the bleed port on the solenoid be open. This allows pressure in the wategate actuator to bleed out of the system so the wastegate can close and the turbo builds pressure again.