Help! Loosing boost at high altitudes!

[Martens199]

Hey guys, I'm currently in golden and riding a 190mcx nytro. Sled ran good coming up to the mountains. Then once unloaded in the parking lot noticed it was over boosting a couple pounds. Once at the top, i lost all boost and the only way to get it to boost was to burped the throttle a bit and held her to the pin. Then the boost would eventually kick in. And it would boost at correct psi.
Any thing ideas???

 

[TurboTime]

Can you provide more details? My first gues would be to check the actuator spring and/or the hose from the actuator to the turbo. The wastegate may be sticking

 

[Martens199]

Well when half way up the mountain around 3-6 thousand feet I would have boost every time I hit the throttle. (Working normally boosting 7-8 pounds). Then when we got to the top 6-8500 ft I did not have any boost, gauge did not show and you could notice it on the sled. So then when I would climb I would have to let off the throttle and then full throttle, off, full throttle a few times and then randomly I would start boosting again. ( around 7-8pounds) until I reached the top of the hill and let off throttle completely. Did this all day. Other than that sled ran and idle completely normal.
This year I replaced exhaust donuts and welded up cracked y pipe. Updated mcx box to a 190hp kit.
Checked waste gate while up there and everything looked free and normal.

 

[Martens199]

Hose to actuator was tight and no cracks, actuator to the turbo waste gate had the normal feeling spring tension. Checked this out on the hill.

 

[kimoajaj]

Since the wastegate seemed fine (do you have the drain hole drilled in it? To avoid it freezing up?) It could be either the TCV valve or the MCX box, or maybe their connectors.

Does anyone know if the TCV valve is able to set the boost to 0PSI or is the base-pressure the lowest it can go? Still if the TCV is acting up I dont think it is able to give you 0 boost.



The MCX box has a vaccum line going into it, this tells the MCX box how much boost you are running and then again it tells the TCV valve wether it should open or close the waste gate.

Make sure your TCV is not full of ice.


Hm

 

[kimoajaj]

If the hose from or to the TCV has a leak it would make your boost pressure higher, not lower.

 

[greenthumb]

Does anyone know if the TCV valve is able to set the boost to 0PSI or is the base-pressure the lowest it can go? Still if the TCV is acting up I dont think it is able to give you 0 boost.
Hm

I replaced TCV last year, with similar symptoms. I do not remember seeing a zero boost situation however, just low, high and erratic levels. Your statement does make sense though.
I went with a manual boost tee because it was readily available, but you do have to adjust it as you change altitude.

 

[rxrider]

If the Boost controller is not working or the lines going to the WG is iced up you will get very high boost numbers which is not good, you may destroy your engine.
The minimum boost you can get is what the WG actuator is set at.
Loosing boost completely tells me you have a leak in your charge tube between the turbo and the intake.

 

[Martens199]

Yeah that's what I thought as well, since I boost at low altitudes but not higher up. So I checked all hose clamps all the way up to the air box and behind. Everything is now tightened up. Still no boost. Couldn't even get it to boost at all today at high altitudes.

 

[kimoajaj]

I don`t have experience with charge air leaks but I do know that the rivets in the tunnel behind the charge air cooler will often touch the cooler, combine it with some vibration and it will eventually make a hole in your cooler.

When I mounted my cooler I put some paint on all the rivets and then put the cooler in place, then took it off to see what rivets where touching it, I then grinded them down so that they didnt touch the cooler.

The rubber hoses between the throttle bodys and the MCX plenum are very short, when we tore Dimebags engine apart, two of the clamps on the hoses had never been correct installed, they had jumped off the hose while tightening it and the mechanic obviously hadnt noticed it. But, Dimebag never had symptons like yours but I guess that if one of the hoses have jumped off or something you could have a leak there too.

Although I do think it should be possible hear the leak while boosting, atleast if it is in the engine bay?

Are you running a manual boost controller at the moment?

 

[Martens199]

Yeah I inspected those throttle body hose clamps very closely couldn't find anything installed incorrectly. I do not have a manual adjuster.
I also tore into the mcx box harness where it tees into the main harness. Found that one of the wires was broken connection, soldered and replaced. This fixed my problem of running on 2 cylinders every now and then, but did not help with the boost problem.
I did have the tunnel cooler off early this year and did not notice and hole worn through.
It's weird how I can boost all day down at lower altitudes but when over 5-6 thousand feet it will only boost the odd time. (Very rarely).
I'm starting to think that when they updated my mcx box to the 190 kit they did something wrong. Because last year with the 180 kit it worked perfect in the mountains.

 

[kimoajaj]

E-mail Erik Marklund at info@mcx.se and tell him what is happening.

If you have no air leaks then I think it has to be the MCX box, or the TCV. I wish I had more knowledge on this system.

As far as I know the MCX box changes the fuel map and also tells the TCV how boost it should run. But, the TCV also measures airpressure (altitude and temperature compensation?) Does anyone know how this system is put together?

Do you have any friends running the 180kit?
Try swapping the MCX box and see if it cures it. If not, try the TCV also.

Hmm

 

[Martens199]

You know I never thought of that, yes I ride with a buddy with a 180hp kit I could easily swap parts.
But as of today I think I might have solved my problem!!! Found that one of the mounting bolts to the plenum (air box) had been stripped out, and there for not sealing. So as any good mechanic would do with no tools or shop to work in, I wrapped the bolt in Teflon tape and tightened up to the best of its ability. Today when I reached the top I was boosting where I did not before. I maybe had it not work once, but the bolt was coming loose. So only tomorrow will tell if it was fluke or not.

 

[rxrider]

it was a leak in the charge tube, what I thought

Glad you have it figured.

 

[kimoajaj]

Great! Awesome! I hope it`s OK now!

Was the bolt still in it`s hole or had it moved out of it?

Are the threads totally shot?