Hi to everyone.I been trying to find the problem of a friends EVO. The car has 32,000 miles -hallman mbc-turbo xs FMIC - Super afc- walbro pump and defi gauges. The car accelerates hard making 1.5 kpa and tapers to 1.4 but when it hits 5,500 RPM the boost starts to bounce back and forth from 1.2 to 1.3 very fast and do the same in all gears. I already checked for vacuums leaks and loose hoses with no luck. I believe the turbo is the problem but i want to hear your opinions. Thanks in advance for any help.

 

I actually have an issue like that if I set my boost controller to ramp up the boost too hard. I'm suspecting it's either a problem with my 1G BOV or the way I've got the BOV hooked up (I'm tee'd off the same line for my boost controller and boost gauge, which I think might delay pressure on the back side of the BOV when boost hits too hard and fast). What BOV is he using?

 

Can it possibly be the car pulling timing which is causing the boost to bounce around.

 

sounds to me like he is floating the BOV. I am running 21 psi and if it holds that for more than a few seconds, like on the highway passing some idiot, then I can hear my BOV sputtering (opening and closing really rapidly). I, too have my boost controller and gauge tapped into the same vacuum line, and I agree that there might be some issues there, but if you're friend has an air intake or a VTA BOV that you can hear, that might tell you if he is having the same problem that I am. not that it really affects performance, but I can't see how it can be good for the BOV.

 

The car has stock BOV and pipes.I already swaped a Greddy type-s and took a test drive and same thing happened.

 

well if the BOV is good, then I dunno.... I can't think of a problem with the Turbo that would make boost bounce around like that, I would think it just wouldn't create enough boost. However, there are many people around here that are FAR more educated about these things then I am... sorry I couldn't help

 

jeff- thanks for your opinion

 

Is there anything tee'd off the BOV hose?

 

Could be boost cut if he's getting to lean with the Safc.

 

Yes there is a vacuun line teed from the piece of vacuun line that goes to the intake manifold the BOV uses the same line after some hard vacuum lines.I'm using the line to monitor boost to my innovate LM1 wideband.I'll remove it tomorrow and see what happens

The car is running rich about 10.4 AF ratios