over boost 25+ psi

[revodsm]

i was having this problem since i bought this car, it had a mbc on it i thought it could be the problem. i removed it and put all lines back to where my 3 books say to. it is the stock turbo stock bov and wastegate. no more boost controller. i have checked all vac/ boost lines and all hoses there are no leaks. it is not smoking but does sputter and mis when boost gets to 16 it goes up really fast my aftermarket gauge goes up to 20 and it will pass that in less than a second.. i need this to be fixed... ideas?

 

[95 'clipse RS]

is the wastgate actuator working properly, or is the wastegate itself stuck closed? first disconnect the wastegate actuator arm from the internal wastegate lever on the housing, and make sure you can move it freely through it's range. if that is fine then you can check the actuator. you will have to have someone rev the car enough to build boost enough to reach 8-12 psi and watch the actuator arm to see if its moving, or another better way is if you have access to an air compressor you can supply low psi (8-12psi) to the actuator nipple and see if its working correctly. it doesnt sound like boost creep/spike at all as you are describing it, so its making me think the wastegate isnt even opening to bypass exhaust away from the turbine. hope this helps you out

 

[rush2252]

funny just before my car quit it was doing this. You dont have a 14 or 16g by any chance do you? If so you might need to bend the nipple on the WG actuator. If it is the above turbo and hasnt been bent then the vaccum line is probably being kinked by your intake and thus acting as an MBC by restricting boost pressure to the WGA.

 

[Calan]

...is the wastgate actuator working properly, or is the wastegate itself stuck closed? first disconnect the wastegate actuator arm from the internal wastegate lever on the housing, and make sure you can move it freely through it's range. if that is fine then you can check the actuator.

Good advice

...you will have to have someone rev the car enough to build boost enough to reach 8-12 psi and watch the actuator arm to see if its moving

You normally can't build 8-12psi of boost by free-revving the engine without a load...i.e. driving down the road or on a dyno. You'll probably be lucky to build 5psi.

...or another better way is if you have access to an air compressor you can supply low psi (8-12psi) to the actuator nipple and see if its working correctly.

Depends on the spring strength of the actuator. His actual spring rate is probably more likely somewhere around 7lbs.

The actual pressure required to open the wastegate when it is hooked up and working depends on a lot of factors, and is not a one-to-one relationship with the amount of pressure actually hitting the boost controller. (For one example, think about the force of the exhaust gases pushing on the flapper, which actually helps the actuator to open the flapper).

But the basic advice of putting pressure to the wastegate and making sure it opens is sound.

 

[95 'clipse RS]

yeah, sorry about that free revving thing, i know it worked on my buddy's supra and it jumped to 8psi for just a moment, but i totally screwed up the fact that this 4 cyl wont produce enough exhaust gas to get it that far unless under load. sorry im stupid

also i didnt take into consideration of the exhaust pushing against the wastegate flapper, very good point!! so for example it may take only 7psi to open a 8psi actuator due to combined pressures, theroetically, but with the engine off it will still take 8psi to open a 8psi actuator.

very good points calan

 

[kenamond]

i was having this problem since i bought this car, it had a mbc on it i thought it could be the problem. i removed it and put all lines back to where my 3 books say to. it is the stock turbo stock bov and wastegate. no more boost controller. i have checked all vac/ boost lines and all hoses there are no leaks. it is not smoking but does sputter and mis when boost gets to 16 it goes up really fast my aftermarket gauge goes up to 20 and it will pass that in less than a second.. i need this to be fixed... ideas?

One quick test is to connect a vaccuum line straight from the compressor outlet nipple to the WGA nipple. This should get you around 9psi boost. If you get ~9psi boost, something's wrong with your boost control lines (clogged or leaking or not routed correctly). If you still overboost, I'd check that the WGA is working. A pressure tester will work for this; add pressure to the nipple and see what pressure you have to apply to get the actuator arm to start extending. I'm not sure of the exact number, but it should be in the ballpark of 8psi.

 

[JayRolla]

Wow Kenamond, where you been buddy!!

 

[Calan]

He seems to pop up at least once every year or so...