MCX Turbo Apex No Boost at Altitude

boostedballz · Dec 18, 2007

I have a 2006 Apex with a stage 2 MCX Kit. Put over 2000 miles on the machine last year without any problems to speak of. First ride out this year it would barely start in the trailer cold. After some convincing and noticing my A/F gauge was reading well into the 14's finally got warmed up and we headed out. Sled seemed to run normal as it should since nothing was changed over the summer. Once I got up to altitude I noticed my boost was down a bit as well as my RPM. I usually have to go a couple of clicks on my boost controller once i'm at altitude to dial in. I continued to play and the higher I got the worse my boost and RPM got regardless of how much I turned my controller. After the weekend of riding I dropped the machine off at my yami dealer thinking I had some sort of intake or exhaust leak. After several hours of going over the entire system he found nothing wrong. I took the machine out again and found it building anywhere from 10-12 lbs and a slow to build. It was about -7 celsius and fairly hard packed conditions. Last weekend it would pull 11-12 in a packed trench but fall on its face in the fresh. The kicker is it runs perfectly as soon as I descend to the truck. After cranking the controller up at altitude it builds as much as 18 lbs on the trail on the way down. I have tried every thing I can think of and talked to several dealers without any change. Any ideas would be hugely appriciated.

LL

obr · Dec 18, 2007

did you change the gas over the summer?

bad gas will kill it...check the mcx box...

boostedballz · Dec 18, 2007

Had straight 100 ll av gas in it when I put it away which isn't supposed to go bad. There was probably 4-6 litres in it when I put it away in May. I filled up with fresh in October.

up-high · Dec 18, 2007

Av gas will go bad. In a hurry. It'll keep in a closed drum(with no air) but not in your gas tank. I don't think gas is the problem. I think gas not getting to the motor could be the problem. Is it pulling the rpm (10500)?

BigFish BC · Dec 18, 2007

do you have the ti headers in it still they were a problem getting to hot & collapsing have a look at them.but what it really sounds like is that you have a boost leak somewhere in your system & your boost is leaking off somewhere instead of building to the point your waistgate dumps to hold your boost.did you have the intercooler off for anything check for lose clamps on the pressure side of the system from the turbo to the intercooler.check your gauge for codes could be one of your sensors not working properly to.the high a/f reading would indicate a air leak too.

mountainbigbull · Dec 18, 2007

I have no real knowledge of these Yamaha engines, but when working with turbocharged diesel engines (that is my background) When an engine has low boost it more a result in something else wrong. So in other words think about what creates boost. You need air, fuel, spark and proper compression to resulting in good combustion. So make sure you have nothing wrong these. Easier said than done right? So if all of that is ok in the diesel world we would look at the turbocharger is self.

So what come to mind for me (keep in mind I have no clue about the yami) What
about the valves? Mabye the need adjusting my guess they have a pretty low clearance and are not allowing the valve to close. Another is fuel filters, and spark plugs. Mabye you just have water in the fuel system from summer storage.

Hope this helps.....

addictedtoboost · Dec 19, 2007

I suggest doing a leak down test, this will rule out or condem the motor.

I had a customer bring me a Turbo RX for a bunch of work, when he put it away last spring, he said it ran fine, we could not even get it to start on Ether, did a compression test found 75 75 65 65 , added oil and it came up some but still under 100 psi, then leak tested the motor and found 65 % leak down in 2 cylinders 45% and 30%.

Linc · Dec 19, 2007

You have an exhaust leak or a boost leak,,,,leak down test the charge system and check the exhaust,as Shane suggested,the Ti headers were a common failure.They get so hot that actually stretch and start to fold and pull away from the clamps,in extreme cases they will start to block off the exhaust and crack.

Climbmax · Dec 19, 2007

Sounds like a boost controller that may have coroded over the summer.
Take that apart and clean it up. The ball and spring is where I would look.

Linc · Dec 19, 2007

That's another place to look,but usually they corrode to overboost.

boostedballz · Dec 19, 2007

Took the boost controller apart last night and cleaned it. There was some moisture but no corrosion. Also checked my bov. How much of an air leak will make a difference. I didn't have anything to pressurise it but when I blew in it it did bleed off some air just from my mouth. I took it apart and cleaned it as it was quite dirty. After I put it together I added a couple of turns of tension and I could not get it to leak. I just dont know if a leak that small could affect it that much.

BigFish BC · Dec 19, 2007

it is surprising how small a leak will cause problems under that much pressure

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MCX Turbo Apex No Boost at Altitude

boostedballz

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obr

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boostedballz

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up-high

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BigFish BC

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mountainbigbull

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addictedtoboost

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Linc

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Climbmax

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Linc

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boostedballz

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