surfmon

iTrader: (6)

Ok, hard problem to explain and I've searched exhaustively.

Stock twins(ported WG)
Pettit SMIC
NO cats.
Simplified Sequentials
Thats all that should matter

This happens 75% of the time under boost. I start in 2nd and punch it. Primary comes on line instantly to 11psi, secondary comes online at 4500rpms and holds at 11psi for a fraction of a second and then I hear the boost dump and it drops to around 3psi. Within miliseconds of the secondary reaching optimal boost, something is telling the secondary blowoff valve to dump it.

And like I said, this is not everytime, just most of the time. Sometimes it holds peak boost all the way to redline. What solenoids would be the main culprits in the situation? Or is it something else altogether?

Any input would be great as I'm about to pull my UIM and redo everything.........again.

Thanks
T

Mahjik

iTrader: (1)

Do you have reliable secondary boost in the upper gears (3rd, 4th and 5th)?

surfmon

iTrader: (6)

no, seems to get worse in higher gears

Jesus loves rotaries

are you sure it sounds like the blow off valve is letting the pressure out and it's not something like the charge relief valve letting it out? sometime's a CRV can go bad and only part part of the time and you will lose boost right when your secondary hits

surfmon

iTrader: (6)

I refer to the CRV as the secondary BOV. It is not the normal blow off sound, more of a gradual WWWWHHHHOOOOOSSSSHHHHHH.

As simple as a bad CRV huh?

Mahjik

iTrader: (1)

The CRV should be open (venting) until around 4000 rpms. It should then close for the rest of the boost pattern. You might verify you have a proper source for the CRV if it's not closing.

ShiftRX7

also check the two vacuum lines to the crv and the bov are not inverted (verify with the vacuum hose diagram)...this could generate something similar to the issue you're reporting

Jesus loves rotaries

yeah sounds like it could be the CRV, my FD was doing something similar, sometimes it would stick and not close and lose boost, I could hear it leaking out the valve attached to it, it made that loud whoooooshing sound too

do you hear a loud fwoom/hoot sound when you let off after you attempt to boost and it doesn't work? that's what mine did too

surfmon

iTrader: (6)

yes I do. If you are describing the sound I think you are, which is hard to do. Sometimes it almost sounds like compressor surge.

I'll do some troubleshooting this weekend and update the thread.

Thanks everyone
T

Mahjik

iTrader: (1)

It's been a while since I've messed with the CRV, but IIRC, without anything attached it's closed. If that's the case, to test if it's not closing you can simply remove the vacuum line to it and see if you have secondary boost. If you do, then your vacuum line source is not correct. If you still don't have secondary boost, then the CRV is not your problem.

surfmon

iTrader: (6)

just so we are clear, when you both refer to the CRV, you are talking about the brown BOV looking valve coming off of the secondary, correct?

David0ff

iTrader: (6)

yes

Mahjik

iTrader: (1)

The valves will have a label on them. The CRV will have CRV written on it and the BOV will have ABV. The CRV is on the rear side of the y-pipe, the BOV (ABV) is on the front side of the y-pipe.

surfmon

iTrader: (6)

what I thought

thanks

dgeesaman

iTrader: (7)

You should also check the hoses leading to the CRV for splits. It gets hot in that area and the hoses can get brittle and leak intermittently.

Also, are you sure you're not hitting fuel cut? Boost gauges can be off by a psi or two in many cases.

surfmon

iTrader: (6)

fuel cut would cause my crv to dump boost??

and I was under the impression that PFC's don't have fuel cut

Sandro

iTrader: (1)

I experienced something similar, like random secondary surging (no boost) and strong relief sound on throttle release. It was a check valve problem, between the vacuum chamber and the UIM.

The lack of vacuum to the actuators of the CCV and TCV would prevent crisp and consistent transition. Another symptom was that even after a correct transition (i.e. CCV open) there were oscillation in boost due to the TCV fluttering.

Transition and boost were fine (but the fluttering) if after "recharging" the vacuum chamber by fully releasing the throttle, then making a pull. But if I would release the throttle a bit (without going into vacuum), go below 3,000 rpm (disengage secondary) then step onto the throttle again, the CCV would not open and the sec turbo surge. Releasing throttle and letting the rpm go down would cause the CRV to open and relief all the compressed air trapped between the compressor and the CCV that had not opened, with an unusually long and loud relief sound.

- Sandro

surfmon

iTrader: (6)

so how did you fix it? That sounds alot like the problems I'm having.

Which check valve/vaccum chambers are you refering to?

Thanks
T

Sandro

iTrader: (1)

Follow the vacuum tube diagrams. A handful of solenoids valves are connected to a "vacuum chamber".

In particular those controlling the CCV and the TCV. The CCV solenoid switches air pressure to one side of the CCV actuator form vacuum to full boost and viceversa (the other side of the CCV actuator is always at the same pressure of the compressor - you can see the actuator is connected to the Y pipe). The TCV actuator sides are connected individually to two separate solenoid valve, one "feeds" pressurized air, the other one vacuum, in order to snap open the TCV flap (high delta pressure at the actuator membrane).

Before opening the UIM and digging into checking through the solenoids, try replacing the check valve I am talking about. Again, follow the vacuum tube diagrams. The vacuum chamber is buried and you cannot see it. The check valve is between it and the UIM. When you make vacuum at the intake (throttle release off boost) it opens and "fills" the vacuum chamber of "vacuum". The check valve "seals" the vacuum chamber.

To access it, remove the "pressure chamber", the black box, then you can see it. Sorry I cannot take pics, someone else may do it for you.

Good luck and do not give up!

- Sandro