Mr. Midas

Okay,

Here we go; my first crack at real how-to writeup of my own on nopistons.com I believe. I don't know how helpful this information will be. I'm sure most active members have done some form of cross-generation parts adaptation on their cars in one form or another for whatever reasons. If this helps anyone or just amuses, that is cool with me. I needed the instructional writeup experience anyways. Why not start with something fairly simple?




If you are swapping /have swapped the S5 VDI intake into an S4 vehicle and want to have a functioning BAC valve, this is one way of getting there on the cheap.

Basically what this modification does is make an S4 Bypass Air Control(BAC) valve compatible with the S5 intake. This is good because then you won't need the S5 valve and the elusive connector it requires. Don't forget though, the S4 connector wire will still need to be relocated to the proper location for it to reach regardless of which valve is used on the S5 intake.

Some people dump the BAC for whatever reason, but since I have removed the air bypass solenoid valve and done the full TB mod I'm glad I kept it. On cold startups it has saved my motor many times from stalling out.






Something could go wrong and you might be left without a working BAC valve... Although I got the procedure right the first time, like all DIY modifications, there is still a chance of screwing it up.















The list of things you will need:



Dish soap & scrub brush.

Brake cleaner.(plastic safe)

Rag or shop towels

Penetrating lube. (WD 40, PB Blaster ect.)

Mini torch or Jet type lighter.(optional)

T20 Torx type wrench or driver.

Crescent Wrench.

Rubber Mallet.

Razor Knife.

Dremel.(optional)

Masking tape.

Circuit board sealer or a quality clear lacquer spray.

Soldering iron with fine point tip.

Thin electronics solder.

Rosin flux.(optional)

Short (2-1/2”) piece of thin 20-22ga stranded wire.

JB Weld.

Rubber bands.

Eye protection, gloves, proper ventilation, common safety sense?



And lets not forget the big one...A little patience!







To make the S4 valve fit right on the S5 intake two things need to be done:



1.The inlet elbow needs to be rotated. - This is fairly easy to do once the torx head set screw is loosened.

2.The plug end of the valve needs to be rotated. - This is where the real work is done and is a little harder to do.





Step 1. Reset the inlet tube angle:



Remove your S4 BAC valve from the junk heap and wipe it clean. It doesn't need to be super clean yet. You'll probably use lubes to get the set screw free.



Now get the torx head set screw loose. Be careful. I've found good luck with PB blaster and/or a mini torch to the heads of small screws like this one. Don't use to much heat or you will ruin the valve...

When you get it loose, take your crescent wrench and grip the inlet tube lengthwise. It should work free and rotate fairly easily. Set the Inlet tube to the correct angle. With the valve sitting on its flange, it's about a 50-60[sup]o[/sup] acute angle toward the connector end of the valve body. Compare with the following pics...







Reset the set screw. Step 1 completed!

Mr. Midas

Step 2. Remove the connector end:



This will need to be broken down into sub-steps...



2a)

Now you need to super clean the valve inside and out. This will prevent contamination of certain areas being exposed and needing soldering and good adhesion with the JB weld. Start with brake cleaner inside, then go over the whole thing with dish soap and scrubber. It should be clean enough to paint.



2b)

Now it's time to (carefully)break the connector end cap free of the valve body. It won't come completely off at first. It will just become loose. That is all we want to happen right now. The end cap has two pins soldered to the solenoid coil wires inside the valve and everything is encased within a potting resin. The pins are located on either side of the center tube and perpendicular to the connector plug. To break the cap free, start out by just gripping the valve in both hands and tug back-and-forth on the cap's plug end using it as a lever. If you're unlucky(like I was) and the cap doesn't get loose by hand, place the opposite end of the valve on a supporting surface and smack the plug end with the mallet, then turn the valve over and hit it from the other side. Be patient. The potting compound is weaker than the plastic end cap, so as long as you don't over do it the potting will eventually give way before the plastic end cap. Check it every few blows. Once it feels a little loose you're ready for the next step!



This pic shows exactly where to hit.(I couldn't resist painting it before finishing the mod)











2c)

Okay, the cap is just a little loose. Now what? Well, the only thing holding the cap on is two extremely thin wires. At this point you should be able to feel the cap rock up and down slightly. It won't be very much. Do not try twisting the cap off! Just keep using the plug end to lever the cap up and down like a sea-saw by hand until the wires break from fatigue and not tension. Again, this is where the patience pays off. It could take a couple minutes.(Think about a twist-tie being bent back and forth until it breaks)

Mr. Midas

Step 3. Prep



3a)

In the picture above you can see where the pins in the cap and the wires in the valve are located. The wires pass through a washer with four small holes. Two holes are empty and any potting compound sticking out of them needs to be removed with a razor knife or dremmel. On the cap side, trim any extra potting sticking up flush and clean around each pin, then give it a couple shots of brake cleaner. If you want, cut some crosshatching for the JB weld to bite into later. After taking care of the potting you need to make the thin coil wires in the valve more accessible for soldering. Do that by slicing the plastic in front them out of the way. I suggest carefully scraping the sides of the wires with the razor knife to expose some fresh copper. Now you're ready to mask and seal!



3b)

Coating the metal top of the valve with a non-conductive barrier insures that the wires and pins don't ground out on the metal during reassembly. I had some real circuit board sealer on hand, But a few coats of a good spray lacquer will do just fine. Use whatever to mask off the valve and the little wire ends.

Mr. Midas

Step 4. Reassemble



4a)

Time to solder. Cut a couple pieces of thin wire just a hair over an inch long(or go longer and trim ends to fit later). Strip about 3/16” off each end and tin with a little solder, and then push an end of each wire next next to each coil wire. Orient them to point counter-clockwise as pictured. There is no positive or negative here. I just happened cut the end off a black and red paired piece of wire and didn't want to waste it...

Now solder the wires up carefully.(Tip: Make sure your iron tip is clean and properly tinned) When soldering the wires to the end cap make sure the connector plug is pointed towards the same side of the valve body as the inlet elbow.













4b)

Check the continuity with an ohm meter. 10.7-12.3 ohms is within spec. If that checks out okay, you're ready to put this sucker back together! Use the JB Weld to fill the recesses in the cap, then fill up the top of the valve. Line the cap up where you want it(reference the pictures.) and press it down until it stops. The cap will sit about 1/8” higher than before due to the wires and pins being in the way now. Clean any excess Epoxy up quickly and use a few rubber bands to hold it securely while it cures up. Check the continuity one more time before leaving it to set up.







Viola! You now have a BAC valve compatible with your S4 wire harness and S5 intake.

Mr. Midas

Oh, for anyone that doesn't know this already from the pictures, this mod only applies to NA's.



How did I do? I know it's a little bass-akwards, but hey, it still works!

ATM my car is probably the only one with an S4 BAC valve fitted to its S5 intake. I feel so, special...

defprun

I'd keep the elastics on even after the jb weld dries up.