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My car has been overboosting like mad for the last few weeks. I have a stock ct26 and a twosrus MBC. I've turned the MBC all the way down (unscrewed it all the way out) and its still jumping to 19psi+ in 2nd - I haven't dared try it in 3rd or 4th.

I'm sure this has something to do with some hoses and such on the wastegate (unless that's broken), but I was wondering if anyone knew of any common problems with this so I know where to look first. Thanks in advance
 

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Common problems are vaccum hose being cracked from the heat. I've had 2 hoses go bad within 1 year of having my AVC-R. Check the entire length of both hoses going to your BC. Bend them and feel them, feel for any hard spots. Heat will make the hose hard and eventually crack.
 

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Assuming your stock TVSV is disconnected, the first thing to do is take out the MBC and hook up the turbo directly to the wastegate actuator.

If it still boosts really high, then rule out leaks in the rest of the boost control system by physically blocking off the 2nd port on the wastegate actuator. Re-inspect the tubing going from the turbo to the actuator by bending it and looking for cracks.

If you still overboost at that point, then use a vacuum pump to test the actuator's diaphram. It should hold a vacuum with the 2nd port plugged.
 

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I'm having the same problem, but i just put a new rebuilt ct26 and greddy intercooler and tko full exhaust. I have the TwosRus MBC hooked up correctly and i'm boosting about 17 psi. I have the MBC all the way counter clockwise. and the TVSV is plugged and the actuator. The vacuum lines to the MBC are brand new. Any other suggestion before i put the actuator back to stock to check it?

Also i have a G-Force Ecu and i believe its set for around 15psi. Could this be causing anything?
thanks
 

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Anything that 1)restricts flow to the actuator (kinked hose, blocked MBC, etc) or 2) allows air to escape from the control loop (loose or damaged hose, open T/VSV port, etc) will increase boost levels.

It really ain't very complicated!

bill
 

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thats the problem, since it is a very simple function, its hard to have problems and not figure it out. I will be removing the MBC tomorrow and Make sure the actuator is opening up at around 7psi. Should i connect TVSV also and leave it capped off.
 

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flyboy said:
If you still overboost at that point, then use a vacuum pump to test the actuator's diaphram. It should hold a vacuum with the 2nd port plugged.
Is this actually a valid test for the actuator? Everything I've seen says to apply positive pressure to make sure the actuator rod extends....
 

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Well, most don't have access to some sort of positive pump that won't leak. The vacuum pumps have really good seals that prevent it from leaking. Don't apply a lot of pressure. 5" is plenty. You're mainly looking for it to hold vacuum, indicating there is no leak.
 

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Barry said:
Is this actually a valid test for the actuator? Everything I've seen says to apply positive pressure to make sure the actuator rod extends....
Tht's the methiod described in the BGB. It not only tests the interity of the actuator, but determines if the actuaor rod is actually opening the WG.

BTW, the actuator almost NEVER fails. The most common problem is leak or a restriction in one of the control hoses, or a physical, mechanical problem with the WG itself.

Once again, its a pretty simple mechanism. Not really much to go wrong.

bill
 
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