I'm going to describe this as best as I can! When I jump into boost with any kind of load at about 5000rpm the BOV releases like it's seeing too much resistance (even at WOT...but worse at partial throttle) and then closes and opens again very fast causing this "boost flutter" that naturally comes with a loss of power. An open rev goes right by 5000rpm smoothly. In first gear WOT (very little load by that time) it seems to be ok (I'm still working on controlling my boost so I have to let up to prevent an overboost situation..this problem is preventing me from properly configuring my boost). My AEM EMS is set to activate VTEC @ 5000 rpm (and it does...or is triggering it at least). I'm tuning with a FJO Wideband o2 sensor so it isn't likely a fuel issue. It will happen @ 5psi or 15psi...doesn't matter. The car is a 2000 si, t3/t4e, tial 35mm, hks ssbv, intercooler, 9:1 comp. It did the same thing with the VAFC hack before the EMS swap. It didn't do it before the hack...I was already using the VAFC and just reprogrammed it for the hack (I can't seem to link the problem with anything I changed for the hack). Engine runs very well until 5500rpm.

 

i read your post like 2 times and i still dont understand what you are talking about. is your bov opening or do you mean your wastegate.?

 

Youneed cliff notes!

Anyway, so your BOV is opening at 5000 rpm, then your boost level flutters?
I'm confused

Try and make a bulleted list of whats going wrong.
Peace

 

I can understand your confusion, it's hard to describe. I'm not sure what's happening specifically (it'd be alot easier to find the problem if I did). When the engine speed reaches about 5000rpm the bov opens and closes erratically (you can hear it and feel it). As a result the boost will pressure up and release very fast. The car will no longer have enough power to accelerate past this point as the boost gauge jumps back and forth from 0 to 10-15psi until I let up on the throttle. The car runs perfect up to 5000rpm, and in 1st gear WOT I can run right past 5000rpm no problem. If you put your car in a high gear and accel 3/4 throttle the car will really have to work to accelerate...when you reach full boost will it hold and continue to accelerate, or will the excessive backpressure combined with your throttle blades partially closed cause your bov to give. Mine always gave in these interstate conditions less than WOT, but now it just gives alot easier even with WOT. Hopefully I didn't confuse you even more. Thanks for trying to figure it out!!


[Modified by nolimits, 5:48 PM 3/13/2003]

 

where does the BOV get its vacuum from?

 

Does this only happen at part-throttle? What BOV are you using?

If it happens at full throttle, my idea is toast. If it happens at part throttle only (the worst is higher gears, or higher rpms, or higher loads (light throttle but up a hill.)) then I think I have the problem....

 

Manifold vacuum...t'd off with cruise and boost gauge. Wastegate is with brake booster. MAP sensor alone. FPR alone.

 

You got the right idea...it used to be rare at WOT, common at partial. Now it's just common all of the time. It's an HKS SSQV. It still seems tight under partial throttle.