10 replies to this topic

[TankRizzo]

Chaps, As part of debugging the car's boost issue, I'm going to bypass the rear boost control solenoid to see if it is at fault. Is it going to cause me any problems by doing this? A lot of the Astra guys seem to recommend it as a long-term modification anyway, but I'm a little suspicious. Thanks in advance.

[siztenboots]

Chaps,

As part of debugging the car's boost issue, I'm going to bypass the rear boost control solenoid to see if it is at fault. Is it going to cause me any problems by doing this? A lot of the Astra guys seem to recommend it as a long-term modification anyway, but I'm a little suspicious.

Thanks in advance.

put in a T and connect the Recirc valve larger diameter plastic pipe direct to the same vacuum supply as used by fuel pressure regulator connection, this is just on the vacuum side of the throttle body.

This will eliminate about 6-7 rubber joins , the solenoid, the vacuum storage box.

If you are getting a prolonged turbo chatter noise when quickly shutting the throttle , this will prove the recirc valve / diaphragm.

Really you need a boost meter on the intake to see what is happening.

[TankRizzo]

put in a T and connect the Recirc valve larger diameter plastic pipe direct to the same vacuum supply as used by fuel pressure regulator connection, this is just on the vacuum side of the throttle body.

This will eliminate about 6-7 rubber joins , the solenoid, the vacuum storage box.

If you are getting a prolonged turbo chatter noise when quickly shutting the throttle , this will prove the recirc valve / diaphragm.

Really you need a boost meter on the intake to see what is happening.

Nice one. Shouldn't take me more than five minutes, got a couple of tees lying round in the garage I can use.

Thanks.

[TankRizzo]

Ok, after bypassing the rear BCS tonight, I am indeed getting quite a bit of chatter on sudden lift-off. Does this mean everything is working ok as regards the recirc?

[siztenboots]

Ok, after bypassing the rear BCS tonight, I am indeed getting quite a bit of chatter on sudden lift-off. Does this mean everything is working ok as regards the recirc?

what does your boost guage record when driving it part throttle between 2,500 to force the turbo to modulate boost , rather than wide open throttle. Plus do you get good vacuum , no leaks now?

[TankRizzo]

I'll plumb the boost gauge back in tonight and see what I get for both tests. Vacuum before I started the bypass was 22inHg. Many thanks Steve.

[TankRizzo]

Well, tried it tonight. Sort of hard to drive it part-throttle and get the turbo boosting at the same time, if you know what I mean. The gauge seems to read between 0-7psi under part throttle, and then WOT gives 19psi overboost and drops to about 12-13psi held. Vacuum is 24inHg. I still have the chatter on sudden lift-off. The OE dv is still working though as I can hear it.

[cheeky_chops]

Ok, after bypassing the rear BCS tonight, I am indeed getting quite a bit of chatter on sudden lift-off. Does this mean everything is working ok as regards the recirc?

i got exactly the same thing when i bypassed the recirc so put it back to OEM (was tring to remove 2500rpm chatter)

[siztenboots]

Ok, after bypassing the rear BCS tonight, I am indeed getting quite a bit of chatter on sudden lift-off. Does this mean everything is working ok as regards the recirc?

i got exactly the same thing when i bypassed the recirc so put it back to OEM (was tring to remove 2500rpm chatter)

scenario 1 - RV connected direct to intake manifold

So when during partial boost , you then rapidly shut the throttle, you should see lots of vacuum in the inlet, this should fully open the Recirc valve.
Provided the diaphragm is in good condition, the boost spike between the turbo and throttle body should have an escape route via the recirc back to intake pipe and atmosphere , instead of stalling the turbo.
Yes you will get a whoosh, instead of a "cha cha cha" stall noise.

[TankRizzo]

scenario 1 - RV connected direct to intake manifold

So when during partial boost , you then rapidly shut the throttle, you should see lots of vacuum in the inlet, this should fully open the Recirc valve.
Provided the diaphragm is in good condition, the boost spike between the turbo and throttle body should have an escape route via the recirc back to intake pipe and atmosphere , instead of stalling the turbo.
Yes you will get a whoosh, instead of a "cha cha cha" stall noise.

I see. So the fact I'm getting compressor stall when the vacuum box and solenoid are taken out of the equation would point to a sticking or otherwise faulty diaphragm in the RV, because it should be opening fully and it isn't.

I take it the box and rear solenoid modulate the boost so that I haven't been getting stall before?

I suppose I could further test this by putting a one-way valve between OE recirc and throttle body vacuum pipe, and plumbing in an atmospheric DV.

Edit: I was also seeing very strong vacuum in the inlet on lift-off.

Edited by TankRizzo, 21 April 2010 - 12:51 PM.

[TankRizzo]

Slight update. Changed recirc tonight for a new one from AET. Still no joy; original seemed to be ok but swapped anyway. Also changed out AMM for a new one. Still getting chatter with vacuum box and inlet BCS disconnected. Still have power dip after 4k. Hmm...I'll try turbo solenoid next. Not many things left.