recently installed an IX turbo & JMF FMIC on my VIII. previously had the OEM FMIC & stock VIII turbo installed. those were the only changes made. the car is running around 22psi.

my problem is that now when I'm driving and I build more the 2psi of boost in any gear the car will buck if I don't completely lift off the gas. This is kind of frustrating on the highway when you are passing someone in 5th gear and you just want to slowly come off the throttle. its also very annoying on track when you just want to lift a little bit to plant the front end, or slow down a hair, and the whole car is bucking back and forth unsettling the weight transfer, not to mention my right foot.

So far to correct the problem I've tried two different BOV's. the greddy type RS (which was on there previously) and most recently the IX MR BOV. I was sure the IX BOV would cure the problem as I've had a very slight issue with this happening using the Type RS BOV on my previous setup, but switching the MR BOV cured it before. NOt sure why it would be different now with a different turbo and FMIC. I realize the IX turbo flows more air, but it can't be THAT much more air.. can it?

other things worth mentioning... the signal line to the BOV is coming straight from the manifold, no t's at all. I have a very small pinhole leak on the JMF FMIC where the end tank was welded to the core. I don't think either of those make a difference with regard to my issue, but I figured someone would mention a boost leak test and having a dedicated line for the BOV. TIA for any help

 

I would check your plugs first if you have not already. Next I would pull the fuel pump and make sure your filter bag is not clogged. Check the stupid stuff first before you throw $ at it, like buying BOV's. If you have the RS, make sure you have the stiff spring in there and crank it down to where you are 5 turns from full stiff. I have the same BOV and thats what I do. So you know my car bucks slightly at partial throttle, but not when I let off the gas. You need to ride with me this Sunday to see if my car matches what your car is doing with partial throttle.
Changing to a 9 turbo and FMIC should not be making your car do that. You got re tuned for the new turbo right? Cause if not that is your problem.

 

It def send likes a BOV prob to me. I mean a stock car can act weird if you let of the gas awkwardly. You could crush the ix valve a little to add spring tension but you will get some compressor surge, depends on if that little bit of drivability is worth it to you.

 

wtf i have had the sameeeeeeeee problem and never been able to fix it. I have an ets 3inch intercooler and stock turbo as well. Mine is almost like the ix bov is opening up to early or something like that and i freakin hate it. I will do anything to help you figure out how to fix this problem lol. Ive been at this for months.

 

thanks for the tips Mike. Pretty sure this is a mechanical problem and not electrical, so that would rule out the tune. Plugs wouldn't be the prob either since its happening when I lift off throttle, same with fuel pump. besides, the car pulls fine @ WOT. When you say you're running the RS valve I think you're referring to the Forge unit, I was referring to the Greddy Type RS.

to address your bucking prob, you might want to loosen the spring pressure on that Forge BOV a little bit. all the BOV does is equalize pressure on both sides of the throttle blade. adding spring pressure will only make it open slower, thats where your buck is coming from I'd bet. give it a shot on sunday and see if it helps... you can always turn it back if not.

Glad I'm not in this one alone. it feels to me like the valve isn't able to let all the air out fast enough. almost like the valve isn't able to react fast enough at half vacuum (part throttle). The OEM valves have a vein that equalize pressure on both sides of the diaphram, thats why its soooo smooth usually. thats why I thought switching back to it over the greddy would be the cure. but now I'm thinking its the spring pressure causing the problem, too stiff of a spring not opening all the way with part throttle.

IIRC the spring in the MR valve is stiffer then the spring in the plastic VIII BOV. I'm going to try the plastic BOV again (even though it leaks @ 14psi) and see if that is the fix. if so, I should be able to adjust the spring pressure on the greddy to very loose and that should be the best of both worlds... hopefully.

Other then that I'm not sure what else to do other then putting the VIII turbo back on and seeing if that really is the problem.

anyone else have input???

 

I had a similar problem (No where near severs though) on my 8. With a tune this went away and the car is alot more drivable now

 

I installed a TiAL vta recently and have had no drivability issues whatsoever. I could do part throttle acceleration and it would not flutter or buck or whatever. Ever since I put on a megan o2 housing it has been doing it, and its annoying as ****.

One thing that has sparked my curiosity is that I have read on here that some people get this with just adding an exhaust on a stock car. I wonder if it has to deal with letting the air in and out evenly. Balance?

Before the o2 housing, I had a perrin intake and filter, boost controller, 80mm catless tbe, TiAL 50mm, e85 supporting fuel stuff, and I tuned it myself.

I'm almost tempted to toss the stocker o2 back on. I already took off the megan and ported the wastegate merger hole a little bigger and didn't notice a difference really...

 

I have the same issue with mine. It occured after I installed my uicp and a 3.5 ets ic.

 

it looks like maybe installing an FMIC is the common thread... anyone else have this issue?

 

My car is bone stock and does the same thing. While not something I particularly like, it is normal for our cars.

edit: I just reread the OP, and it is not what my car does.

 

I don't believe its normal. my VIII never did it and I've driven IX's before that didn't do it either. Besides, there would be dozens of treads with pissed off EVO owners if that was the case. who would buy a car that bucks on the highway?

 

+1 When my car was bone stock, it never did such a thing.