Johnny_Cracker

iTrader: (1)

Anybody ever actually disassemble a BAC valve to get in and physically clean it/check it?

When I got the 7 it was in storage and a mouse set-up in the airbox and I'm wondering if **** may have got sucked back and maybe got into the bypass hose and lodged in the BAC.

This is next on the list for fixing the idle surging/seeking issue the SE seems prone to. Ideally I'd like to open it up and clean/reassemble to be certain it's not the BAC, but don't want to brick it in the process...

I've found little on the BAC other than removal threads.



Thanks

clokker

iTrader: (2)

I'm thinking that after 20-some years, if it were possible to disassemble/service the BAC, we'd know about it.

Johnny_Cracker

iTrader: (1)

Yeah you'd think right?

So clokker says "NO",

Anyone else?

Johnny_Cracker

iTrader: (1)

Here's a look at it:



It looks like it can be broken down further imo.

In fact I tried to wiggle it apart at the flange after loosing the bolts but it's tight.

southsidecox

iTrader: (52)

id think just to shoot some carb cleaner in it to loosen any grime or junk would be ok,ive had great results doing that over the years followed by the thin clear silicone spray to lubricate moving parts like diaphragms,plungers,etc. worked great on sticky 2nd gen bac valves

Johnny_Cracker

iTrader: (1)

That sounds more practical at this point. I don't really wanna force the thing apart if I don't have to. I'll give your method a try and see how it works out. Thanks ssc

Carzy Driver

Rising RPM - Product - IAC Manifold

arghx

iTrader: (3)

I've cut one in half (they're cheap parts and many spare ones exist). You can't really disassemble them for service. There's a magnetic coil and a plunger in there.

beefhole

iTrader: (29)

Which BAC valve is that?! That's not the 2nd gen valve.

Johnny_Cracker

iTrader: (1)

You're right. It's for an S3 SE. The second gen section is where 13b FB owners end up spending lots of time.

I went back to re-read the great article on SE idle problems by David Lane found here:
Solving GSL-SE Idle Problems

First time I read it I wasn't focusing on the BAC yet, so I breezed thru that part. Glad I went back since he details how to separate the ACV from The BAC (where the yellow arrows were in pic above) and physically get a finger in there to check if it's functioning properly.

Since I know I can safely disassemble the unit at that point I'm more confident putting a little more force behind splitting the joint now.

I'll let you guys know how it turns out.

TonyD89

iTrader: (10)

If it was put together, then it can come apart. That doesn't mean that some of the methods used to build the device are permanent by design but, there is usually some way. Undo obvious things screwed together, bend up tabs on stamped parts, grind out stakings with a Dremel or pencil grinder, unpress parts, etc...

beefhole

iTrader: (29)

It's not worth it; it will break. There is what looks like a hex screw on one end, but it ends up stripping/breaking. I've tried.

For everyone that every took it off, there is one for sale. Also there is a thread about a cold idle issue afterwards

arghx

iTrader: (3)

Whoa there, the S3 BAC valve is a completely different design than the S4. It's basically vacuum modulated instead of running off a single pulsewidth modulated solenoid.

S4 design, which is pretty similar to most late 80s/90s linear solenoid type idle air control valves:



S3 design, which is basically prehistoric stuff you would find on old Bosch Jetronic systems:

Johnny_Cracker

iTrader: (1)

Yeah totally... I didn't realize the 2nd gen setup didn't use the vacuum diaphragms. I wish there was a 13b FB specific section

I'm confused between what David Lane says about valve engagement and what mine does... His article says the bac is CLOSED at rest and the valve is pushed out. To OPEN the valve apply vacuum to the vacuum diaphragm nipple and the valve moves in and opens.

I think he might have his "OPEN"s and "CLOSED"s reversed. If you look at the 85 FSM Section 4B-52 that arghx so kindly provided above (the second one) we can see that from the diagram it's impossible for the BAC valve to be CLOSED while in the out position.

In both cases the valve moves in under vacuum and is out when vented. Using these two coroborating descriptions while looking at the BAC diagram in the FSM shows it cannot be closed and out.....ever.

So moving on. I checked the BAC and ASV, cleaned them and reassembled the unit. I polished it up a bit too. Just need to reinstall and do the FSM vacuum and vent solenoid valve checks to make sure the vacuum diaphragm moving the BAC is getting proper air.

Judging by how few original miles are on the car (54k) I'm not surprised the BACs innards wern't too dirty. That's also why I don't think it will fix the idle seeking bounce I experience frequently. At least I learned a lot in the process though.