BAC valve coolant hoses?

Justen · 10-16-2009, 01:11 PM

I was just wondering if you guys know off the top of your head where the coolant hoses from the BAC-valve run to. I initially removed all the emissions and idle control stuff during my rebuild, but i think i'd like a more consistent idle again. I believe one theres a small coolant feed from the throttle body, but i did the t.b-mod and removed thermowax so i just wasnt sure if the BAC is usable at all for me.

Also, will it still operate corectly without the Air Bypass Solenoid? or will the two only work in conjunction with one another?

Justen · 10-16-2009, 01:13 PM

...1990 Turbo II S5

NoDOHC · 10-18-2009, 12:33 AM

You don't have to have the coolant lines connected to have the BAC work. All you need is the line from the intake duct and the wiring.

It has been too long since I saw a stock TII I can't remember if it comes from the back of the engine or from the front of the engine, sorry. Although I can tell you that it likely is connected between that coolant port at the back of the engine and the coolant port on the back of the water pump housing.

You could check the engine section of the FSM.

I think the Air Bypass solenoid only operates right after initial startup, while the BAC operates all the time.

Justen · 10-19-2009, 11:18 AM

Okay, nice.
Good to know i dont need the coolant hoses, cuz i think i hacked them up to use them for something else. I'll check some of the vacuum diagrams...

thanks again

Max777 · 10-19-2009, 02:08 PM

yeah, you dont need the hoses for the BAC, but you do need them for the thermowax.

I left my thermowax in, and right now the hose from the lower nipple on the turbo TB to the nipple on the rear iron is pissing me off.... make sure you use the stock-like hose, I tried using hose from autozone, and it was hell trying to get it onto the nipple....

As far as the top hose, you can use the "water pump housing -to- BAC hose and just run it to the top of the TB instead.

PS: Remove your secondary vaccum operated throttle plates if you feel like it, they are useless after the emissions are gone.
BUT DONT remove the thermowax pellet!

NoDOHC · 10-19-2009, 11:09 PM

What is wrong with removing the thermowax pellet? I don't have it on my '86 and it starts and runs fine. (It idles a little slower, like 400 rpm, on a cold day, but it still idles).

rx4ur7 · 10-20-2009, 12:39 PM

Forward hose goes to water pump housing. Rear goes to thermowax pellet.

Autozone/checker hoses will not fit correctly because they are not metric. Cleanest easiest is to use mazda. Pricey yes but fit right and will not leak. Using metric hose would be my only other option. That way you can stay with the spring clamps.

Thermal pellet is for cold start. Effects driveability and emissions(during warm up).
Removing it can be hard on the motor because it does not come to full operating temps a fast, especially for a daily driver. In the long run it can shorten engine life.

Race cars not so much because you are usually sitting in the car holding it at 1500/2000 for a while.

Justen · 10-20-2009, 05:58 PM

Well i dont need the coolant lines because i have removed the thermowax anyway, i dont really see the point of having it in my case. Just feather the throttle at startup for a minute or two. With the amount of time and money i put into the rebuild, i'd have to be an idiot to drive the thing without letting it warm up first and risk damage to any part of the motor, so the thermowax is kinda worthless to me.

But for the BAC, which i do want to hook back up for better idle (even after warmup), I just need that one Vacuum line ...and it leads back to the TB or to the rubber intake duct? sorry, a little confused

NoDOHC · 10-20-2009, 08:35 PM

It comes from the rubber intake duct. The BAC MUST take air in through the AFM or the engine will not idle (it will be un-metered air). If you take it from after the throttle plates, it is not functioning as a BAC (bypass air control) which is supposed to bypass the throttle plates and allow air into the engine.

Justen · 10-21-2009, 12:48 AM

Okay, perfect
So i simply run a vac hose from the top of the BAC valve to one of the intake duct nipples. Great, thanks guys.

10-16-2009, 01:11 PM	#1
Justen In Too Deep Join Date: Jun 2009 Location: Clifton, NJ iTrader: (3) Posts: 112 Rep Power: 16	BAC valve coolant hoses? I was just wondering if you guys know off the top of your head where the coolant hoses from the BAC-valve run to. I initially removed all the emissions and idle control stuff during my rebuild, but i think i'd like a more consistent idle again. I believe one theres a small coolant feed from the throttle body, but i did the t.b-mod and removed thermowax so i just wasnt sure if the BAC is usable at all for me. Also, will it still operate corectly without the Air Bypass Solenoid? or will the two only work in conjunction with one another? __________________ 1990 TII, fresh rebuild Atkins rebuild kit, RA apex seals Med. Streetport, TB mod, rebuilt turbo, ported wastegate, GodSpeed FMIC RacingBeat Turbo-back straight exhaust, Bonez test pipe, emissions/nest removed hks intake, Walbro, Profec B spec-2

10-16-2009, 01:13 PM	#2
Justen In Too Deep Join Date: Jun 2009 Location: Clifton, NJ iTrader: (3) Posts: 112 Rep Power: 16	...1990 Turbo II S5 __________________ 1990 TII, fresh rebuild Atkins rebuild kit, RA apex seals Med. Streetport, TB mod, rebuilt turbo, ported wastegate, GodSpeed FMIC RacingBeat Turbo-back straight exhaust, Bonez test pipe, emissions/nest removed hks intake, Walbro, Profec B spec-2

10-18-2009, 12:33 AM	#3
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	You don't have to have the coolant lines connected to have the BAC work. All you need is the line from the intake duct and the wiring. It has been too long since I saw a stock TII I can't remember if it comes from the back of the engine or from the front of the engine, sorry. Although I can tell you that it likely is connected between that coolant port at the back of the engine and the coolant port on the back of the water pump housing. You could check the engine section of the FSM. I think the Air Bypass solenoid only operates right after initial startup, while the BAC operates all the time. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

10-19-2009, 11:18 AM	#4
Justen In Too Deep Join Date: Jun 2009 Location: Clifton, NJ iTrader: (3) Posts: 112 Rep Power: 16	Okay, nice. Good to know i dont need the coolant hoses, cuz i think i hacked them up to use them for something else. I'll check some of the vacuum diagrams... thanks again __________________ 1990 TII, fresh rebuild Atkins rebuild kit, RA apex seals Med. Streetport, TB mod, rebuilt turbo, ported wastegate, GodSpeed FMIC RacingBeat Turbo-back straight exhaust, Bonez test pipe, emissions/nest removed hks intake, Walbro, Profec B spec-2

10-19-2009, 02:08 PM	#5
Max777 Pirate Join Date: Mar 2008 Location: Central IL iTrader: (5) Posts: 1,323 Rep Power: 18	yeah, you dont need the hoses for the BAC, but you do need them for the thermowax. I left my thermowax in, and right now the hose from the lower nipple on the turbo TB to the nipple on the rear iron is pissing me off.... make sure you use the stock-like hose, I tried using hose from autozone, and it was hell trying to get it onto the nipple.... As far as the top hose, you can use the "water pump housing -to- BAC hose and just run it to the top of the TB instead. PS: Remove your secondary vaccum operated throttle plates if you feel like it, they are useless after the emissions are gone. BUT DONT remove the thermowax pellet! __________________ Rotaries:They are NOT that complicated!

10-19-2009, 11:09 PM	#6
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	What is wrong with removing the thermowax pellet? I don't have it on my '86 and it starts and runs fine. (It idles a little slower, like 400 rpm, on a cold day, but it still idles). __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

10-20-2009, 12:39 PM	#7
rx4ur7 Rotary since 1972 Join Date: Nov 2008 Location: Tucson iTrader: (0) Posts: 231 Rep Power: 17	Forward hose goes to water pump housing. Rear goes to thermowax pellet. Autozone/checker hoses will not fit correctly because they are not metric. Cleanest easiest is to use mazda. Pricey yes but fit right and will not leak. Using metric hose would be my only other option. That way you can stay with the spring clamps. Thermal pellet is for cold start. Effects driveability and emissions(during warm up). Removing it can be hard on the motor because it does not come to full operating temps a fast, especially for a daily driver. In the long run it can shorten engine life. Race cars not so much because you are usually sitting in the car holding it at 1500/2000 for a while. Last edited by rx4ur7; 10-20-2009 at 12:46 PM..

10-20-2009, 05:58 PM	#8
Justen In Too Deep Join Date: Jun 2009 Location: Clifton, NJ iTrader: (3) Posts: 112 Rep Power: 16	Well i dont need the coolant lines because i have removed the thermowax anyway, i dont really see the point of having it in my case. Just feather the throttle at startup for a minute or two. With the amount of time and money i put into the rebuild, i'd have to be an idiot to drive the thing without letting it warm up first and risk damage to any part of the motor, so the thermowax is kinda worthless to me. But for the BAC, which i do want to hook back up for better idle (even after warmup), I just need that one Vacuum line ...and it leads back to the TB or to the rubber intake duct? sorry, a little confused __________________ 1990 TII, fresh rebuild Atkins rebuild kit, RA apex seals Med. Streetport, TB mod, rebuilt turbo, ported wastegate, GodSpeed FMIC RacingBeat Turbo-back straight exhaust, Bonez test pipe, emissions/nest removed hks intake, Walbro, Profec B spec-2

10-20-2009, 08:35 PM	#9
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	It comes from the rubber intake duct. The BAC MUST take air in through the AFM or the engine will not idle (it will be un-metered air). If you take it from after the throttle plates, it is not functioning as a BAC (bypass air control) which is supposed to bypass the throttle plates and allow air into the engine. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

10-21-2009, 12:48 AM	#10
Justen In Too Deep Join Date: Jun 2009 Location: Clifton, NJ iTrader: (3) Posts: 112 Rep Power: 16	Okay, perfect So i simply run a vac hose from the top of the BAC valve to one of the intake duct nipples. Great, thanks guys. __________________ 1990 TII, fresh rebuild Atkins rebuild kit, RA apex seals Med. Streetport, TB mod, rebuilt turbo, ported wastegate, GodSpeed FMIC RacingBeat Turbo-back straight exhaust, Bonez test pipe, emissions/nest removed hks intake, Walbro, Profec B spec-2

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