How To: Converting NA BAC to Tii BAC
07-01-12, 03:34 PM
#1
How To: Converting NA BAC to Tii BAC
We found that our N370 Tii BAC leaked when unpowered. When we'd blow into the cad-plated intake elbow air would pass thru the square port. Upon closer inspection we found that the rubber gasket for the valve was torn.
We cycled it with a 9v battery and the solenoid works but because of the torn gasket sometimes it would seal and sometimes not.
As of this writing, Mazdatrix has new N370 BACs for $595.11.
Like many people we did a Tii swap so had an N350 NA BAC in our large pile of boxed up NA parts. AGreen had mentioned that sometimes the cad-plated elbows can leak because they are press fit with a screw as a just-in-case. So I figured they might be interchangeable and there may be more leftover N350 NA BACs around than N370s.
The electrical terminal end points straight down on the N350 and is angled 45 degrees out on the N370. The cad-plated elbow on the N350 is rotated out 45 degrees while the N370 is parallel.
Our BAC electrical plug barely stretched to the BAC I assume because it is an NA harness. And since I'm not sure if I can rotate the electrical end without screwing something up I'm leaving it alone. The bonus is that this eliminates the tension on the electrical plug.
I would not touch the 5mm allen the "appears" to hold the brown electrical cap on. I believe it actually adjusts the solenoid plunger. I do not know how to remove the brown cap to rotate it.
Like a JDM N370 BAC, the USDM N350 BAC does not have an idle set screw. So you'll have to use the same idle set procedure as someone using a JDM Tii. I have never seen a write-up on how to do that.
TOOLS & SUPPLIES
T20 Torx screwdriver bit.
Permatex Sensor-Safe Silicone Gasket Maker
Before you begin test the N350 BAC.
First I took the set screw retaining the cad-plated elbow out. You'll need a T20 torx for that. Harbor Freight has a cheap 100 Piece Security Bit Set that has it.
Then I used a 12" 3/8 socket extension and stuck it in the cad-plated elbow and spun it out of the BAC. It's a press fit but it spun out reasonable easy.
Then I put the elbow in the quick chill section of the freezer which will shrink it making it easier to put back in. I sprayed both the in and out ports of the BAC with carb cleaner and then blew it out and dry with compressed air.
After 20 minutes I smeared some sensor-safe silicone (copper Permatex in my case) on the walls of the hole the elbow fits in and the outside of the elbow. Just a little to make sure it seals perfectly since the slightest vacuum leak freaks out the ECU. Then I used the 3/8" socket extension and wound it back in. Make sure you get it in as far as you can because there isnt a lot of clearance between the bottom of the elbow and the Air Control Valve. And of course make sure it is parallel to the body of the BAC.
Using the T20 torx replace the set screw. You do not need to predrill the elbow as the pointy end will take care of it for you.
I didnt realize this but the coolant passage separates easily by removing the two Phillips head screws. Coolant does not enter the BAC and Mazda runs coolant there to keep the BAC from freezing up. If the nipples on your coolant passage are broken (as ours was when the engine arrived from TigerJapanese) you can get a new nipple from either a N350 or N370 BAC. They are interchangeable. If you live in a warm climate like we do, you can probably bypass it completely.
We have a Corksport hot pipe (I think they call it a "power pipe") which as a smaller nipple than the corresponding one on the BAC. I used a 5/8" rubber hose on the BAC elbow (you can see it in the second picture above) and inserted a 10mm ID silicone hose into it. It's a tight fit on both ends but seals up very well. Used a little Dawn dishwashing detergent as lube. I also used an Xacto to flare the inside of the 10mm hose so it would go on the Corksport nipple easier.
That's pretty much it. We haven't tested it yet but don't anticipate any issues. We were suffering from random idle behavior and hope the torn BAC valve gasket is the culprit.
We cycled it with a 9v battery and the solenoid works but because of the torn gasket sometimes it would seal and sometimes not.
As of this writing, Mazdatrix has new N370 BACs for $595.11.
Like many people we did a Tii swap so had an N350 NA BAC in our large pile of boxed up NA parts. AGreen had mentioned that sometimes the cad-plated elbows can leak because they are press fit with a screw as a just-in-case. So I figured they might be interchangeable and there may be more leftover N350 NA BACs around than N370s.
The electrical terminal end points straight down on the N350 and is angled 45 degrees out on the N370. The cad-plated elbow on the N350 is rotated out 45 degrees while the N370 is parallel.
Our BAC electrical plug barely stretched to the BAC I assume because it is an NA harness. And since I'm not sure if I can rotate the electrical end without screwing something up I'm leaving it alone. The bonus is that this eliminates the tension on the electrical plug.
I would not touch the 5mm allen the "appears" to hold the brown electrical cap on. I believe it actually adjusts the solenoid plunger. I do not know how to remove the brown cap to rotate it.
Like a JDM N370 BAC, the USDM N350 BAC does not have an idle set screw. So you'll have to use the same idle set procedure as someone using a JDM Tii. I have never seen a write-up on how to do that.
TOOLS & SUPPLIES
T20 Torx screwdriver bit.
Permatex Sensor-Safe Silicone Gasket Maker
Before you begin test the N350 BAC.
- Blow into the elbow. No air should pass thru at all.
- Measure the resistance between the two contacts. It should be Resistance: 10.7-12.30 ohms.
- Using a 9v or a car battery apply power to the contacts. I found that the test leads from my DMM worked great for this. The ends that plug into the DMM fit nicely on the 9v battery terminals and the needle ends made touching the contacts easy. Have someone blow into the elbow (a length of 5/8" ID hose makes this easier) while you touch the contacts. Air should flow when power is applied and stop when you release. It's been said on the forum that leaving power on too long will burn out the solenoid but the FSM does not make the same warning.
First I took the set screw retaining the cad-plated elbow out. You'll need a T20 torx for that. Harbor Freight has a cheap 100 Piece Security Bit Set that has it.
Then I used a 12" 3/8 socket extension and stuck it in the cad-plated elbow and spun it out of the BAC. It's a press fit but it spun out reasonable easy.
Then I put the elbow in the quick chill section of the freezer which will shrink it making it easier to put back in. I sprayed both the in and out ports of the BAC with carb cleaner and then blew it out and dry with compressed air.
After 20 minutes I smeared some sensor-safe silicone (copper Permatex in my case) on the walls of the hole the elbow fits in and the outside of the elbow. Just a little to make sure it seals perfectly since the slightest vacuum leak freaks out the ECU. Then I used the 3/8" socket extension and wound it back in. Make sure you get it in as far as you can because there isnt a lot of clearance between the bottom of the elbow and the Air Control Valve. And of course make sure it is parallel to the body of the BAC.
Using the T20 torx replace the set screw. You do not need to predrill the elbow as the pointy end will take care of it for you.
I didnt realize this but the coolant passage separates easily by removing the two Phillips head screws. Coolant does not enter the BAC and Mazda runs coolant there to keep the BAC from freezing up. If the nipples on your coolant passage are broken (as ours was when the engine arrived from TigerJapanese) you can get a new nipple from either a N350 or N370 BAC. They are interchangeable. If you live in a warm climate like we do, you can probably bypass it completely.
We have a Corksport hot pipe (I think they call it a "power pipe") which as a smaller nipple than the corresponding one on the BAC. I used a 5/8" rubber hose on the BAC elbow (you can see it in the second picture above) and inserted a 10mm ID silicone hose into it. It's a tight fit on both ends but seals up very well. Used a little Dawn dishwashing detergent as lube. I also used an Xacto to flare the inside of the 10mm hose so it would go on the Corksport nipple easier.
That's pretty much it. We haven't tested it yet but don't anticipate any issues. We were suffering from random idle behavior and hope the torn BAC valve gasket is the culprit.
07-01-12, 07:17 PM
#2
Worked marvelously. We futzed with the three idle adjustment screws on the JDM throttle body (with our PVC TMIC in place) and the TPS and got the idle to the mid 700s. When the rad fan comes on the idle drops to low to mid 700s. When the A/C was turned on the RPMs jumped to 850-875. It never had that dramatic effect before.
One thing that threw us for a bit was we have an ISC jumper grounded to the main fuse box bolt but it wasnt getting good ground. We moved it to the negative terminal on the battery and we had an obvious change in the RPMs.
Hope this helps someone who has BAC issues.
One thing that threw us for a bit was we have an ISC jumper grounded to the main fuse box bolt but it wasnt getting good ground. We moved it to the negative terminal on the battery and we had an obvious change in the RPMs.
Hope this helps someone who has BAC issues.
07-01-12, 09:15 PM
#4
Yeah, if AGreen hadnt mentioned that the cad-plated elbow can leak, it may not have occurred to me that I could repurpose the N350 BAC. That's why I decided to write it up so if someone else needs a BAC they can see that it has been done before, its easy-peasy, and it works.
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