I pulled the dynamic chamber on my 1984 GSL-SE for the first time to have injectors cleaned/checked, replace fuel rail hoses, etc. and have noticed that I seem to be missing the "vacuum chamber" that goes between the vacuum solenoid valve and the BAC valve. Attached are pictures for reference. It looks like the missing vacuum chamber has been bypassed by a piece of pipe on my car, so I have the following questions:
1. l'm assuming that a previous owner must have done the removal/bypass. The microfiche doesn't indicate it was a deleted part at anytime during 1984 production. Is the vacuum chamber critical? Car has been running fine the 10 years that I've owned it, other than an intermittent temporary power loss condition that sometimes rears its ugly head and strands me on the road side (which I'm trying to chase down).
2. Searching for N304-13-775B doesn't reveal any readily available for sale (no hits on Mazdatrix, Atkins). If it is critical, anyone got one for sale?
3. Anyone have a picture where it bolts onto the engine?
Thanks!

 

Is that a pic of your engine or one that has the actual vacuum chamber? You will need some GSL-SE experts like @LongDuck to help on this.

 

That's a pic of my engine - the tube pointed to by the red arrow is where I think the vacuum chamber is supposed to go.

 

as i recall the chamber bolts to the top of the engine, there is that threaded hole right in the center.
i believe since the chamber is hollow, its just some kind of damper, although who knows. i think it would work ok without it.

 

The vacuum chamber shown works as a volume compensator. The Vent & Vacuum Solenoid SET is two wired electrical actuators which open and close valves to operate the Bypass Air Control Valve - which has 2 functions: Idle increase when the A/C or another drain kicks on, and Idle compensation (up or down) within certain limits.

The vacuum chamber allows intake manifold (RE-EGI Chamber) pressure to be stabilized with a larger volume of air contained within that chamber. The larger volume dampens out rapid fluctuations due to the RE-EGI air being the primary intake source for the engine. Under hard acceleration and even braking, vacuum sensed from the port which drives the V&V Solenoid Valves would be all over the place. The vacuum chamber helps with this.

Functions of the BACV are covered in depth elsewhere on this site if you search. At this point, just know that your idle compensation circuit will operate best WITH the vacuum chamber installed (or Mazda wouldn't have included it) but you could replicate this by using a longer, coiled length of vacuum hose and get about the same effect. The idea is to isolate the pressure fluctuations from the switching valves by adding air volume in the path.

 

Thanks @LongDuck for your expertise - I have tracked down a vacuum chamber and will be installing to get back to the OE design. It's a head scratcher why mine was removed, but then again, when I bought the car it idled horribly and I found out once I got it home that there was a rag stuck in one of the throttle body throats. Removed that, problem solved. You just never know what previous owners have done.

 

Hi @LongDuck while I have you on the phone, so to speak - any thoughts about the intermittent problem I mentioned in my initial post? For the most part, the car runs great, but every so often it goes into "stumble mode", no power, car basically limps to the roadside and stops. I've had it happen at low and high speed cruising - most times, it's been while the car has been running for awhile, so it could be temperature-related, but I've had it happen a couple of times after cold startup within 100 yards after leaving my house. After resting, the car always recovers and runs fine until the next time it happens. I've had it go 200-300 miles in between "stumble mode" instances - feels like a sudden lean mixture situation, based on my experience with other cars.

Over the past couple of years I've been going through all the systems:
1. Car is bone stock, other than I run pre-mix (previous owner removed the OMP). ~85K miles. Dowel pin leak about 5 years ago, engine was rebuilt/resealed by Banzai Racing. Banzai stated the engine internals were in great shape, thought it was probably the result of running pre-mix, only needed to be resealed.
2. New OEM fuel pump and filter, dropped the tank, very minimal rust in a couple of places, no debris in the pickup screen. New rubber hoses in the fuel line from the tank to the intake (except the two under the dynamic chamber). Fresh fuel/pre-mix/stabilizer.
3. New igniters/thermal paste, new coils. Plugs/wires were done in the not too distant past.
Still had the problem occur last fall after the above work.
Currently going through the intake-related items - cleaning throttle body, new pressure regulator and pulsation damper, replace any bad vacuum hoses, sent out injectors (ND units, don't think they are OE) which tested/balanced fine. One of the fuel rail mounting bolts was finger-loose, but no other anomalies noted. Thermo sensors test ok, replaced the delay valve which was out of spec. Bench tested the BACV and both parts of it tested ok. I'll end up going through all the other fuel/emission sensor testing in the FSM once I have everything back together.

Searched the threads here and elsewhere over the past couple of years for someone else that might have had a similar condition, but didn't turn up anything that seemed to point out something I haven't addressed. Sorry for the long post, I would certainly appreciate any pearls of wisdom you might have related to this.

 

its easy to forget about the chamber, and when you pull the intake, snap it in half

 

To me this sounds like ignitors over heating or failing. When this happens try swapping the leading and trailing ignitors. I know you replaced them but its the first thing that popped out to me about it.

 

Possibly Ignitors, but I'm thinking Fuel Filters (3 of them). Any rust AT ALL in the tank is going to be a problem.

To keep this SE Vacuum Chamber thread clean for posterity, create a new post with your stumbling thread and let's get more eyes on this.