RotorJoe

What is the serge tank assembly for? I think it is the serge tank. This is the device that is on the firewall side of the upper intake manifold right after the throttle body. It looks like their used to be a vacuum tube holed to it and there is a piston rod that would move (with vacuum or pressure, not sure) When I tried to look it up in the FD manual, I didn’t get to far. All it stated was hook the vacuum tube to it and I was not sure if that was the serge tank or not. Either way it mounts to the firewall side of the upper manifold right after the throttle body.

As I was driving home I gave it some boost and as I let off, I heard the BOV (as normal) then all I heard was a loud PSSSSSSSSSS noise coming from under the hood. Right then my idle started to hunt from 800 rpm to about 1500 rpms. I then gave it some gas and I noticed that when I step on the throttle the noise goes away but as soon as I start to let off it comes back. I then gave it some gas under load, boost level was a little low and inconstant, although the noise would disappear. As soon as I let off the gas it would come back. As I played with it some more, I noticed that the PSSSSSS noise would go away any time I started to go positive boost levels, but then as soon as the boost gauge would drop to negative boost level the noise would come back. At my friends house we were able to put that thing back in and pop it back out under boost. It is missing a bolt that holds it in. I will replace it and get on my way.

I am wondering what that thing is for? I have a stage 2 ported motor with a PFC and commander unit. I also have an aftermarket fuel pump with 1600cc secondary injectors. I am running parallel stock ported turbos with a large front mount IC. Rad is a fluidine (sp) and two electric fans. I also have a 3’’ dp with full exhaust. When I bought the car (few months ago) the device I am talking about was never hooked up (no vacuum lines running to it), so I figured that it was some thing for a stock set up. Either way this dam thing popes out and I believe I lose manifold pressure. This makes the car idle funny and boost inconsistent.

Q’s:
What is this for?
Do I need it hooked up?
If so, where does the vacuum lines connect to?
IF not, could I seal it with a home made cover plate and gasket (capable of holding a 14psi)?

P.S. I was only boosting 7 psi (half a bar) and after the engine is tuned and broken in, it should see regularly 14psi (1 bar).

RotorJoe

I have done a search and only got two hits and they talked about the ASAT and fuel. This is neither.

paw140

I've had the UIM off several times, and I have no idea what you are talking about. Is it bolted to the UIM? There is a bunch of stuff back there for actuating the secondary throttle plates, and some accelerated warm up stuff, but nothing that would 'pop out' and cause a vacuum leak. There is also and idle control motor back there.

RotorJoe

I will try to take a picture of it and then post it. It is right behind the TB on firewall side on the manifold.

johnchabin

iTrader: (2)

Are you talking about the actuator for Double Throttle?

http://robrobinette.com/double_throttle.htm

RotorJoe

Yes it is, Thanks for that link. It is the actuator that came out of my maniflod. The pictures I just took are greater the 102K so I can not post them. Thanks again for figuring out my non-since, that link helps. It sound like my was disabled due to the lack of vacuum tubes hooked to it. I am reading more of the link, but the actuator is what I am talking about. One bolt is missing and under boost it pops out and I have a large hole in my maniflod leaking air, hence the PSSSSSS noise.