Bypass valve failures

[Tom @ Fast Forward]

Well, I may have an answer as to why there have been a few bypass valve failures. I think that connecting the vac/boost line to the valve from the intake manifold is a bad idea. The one on my 99 had a diaphragm failure last week. I have installed a new one and moved the hose to the VDB and it works just the same. However, the bypass diaphragm is no longer being punished with all that boost. The VDB only sees vacuum, driving the valve to bypass mode, and atmospheric pressure, driving the valve to boost mode.

I recommend this conversion to everybody. All I did was pick up a 1/4" Tee from the hardware store and cut one of the 1/4" lines going to the VDB. Install the tee and move the Bypass hose to it. Then either cap the bypass fitting on the manifold or remove it and replace with a pipe plug.

The operation will be the same but I expect the life of the bypass valve to be significantly extended.

[dave_v]

Hi Tom,Thanks for the info,but i am unsure as to what it all means,any chance of a picture ?.cheers Dave

[Tom @ Fast Forward]

Move the end of the Bypass hose from the Intake Manifold to the VDB and plug the Intake Manifold. If you don't have an unused port on the VDB, simply put a TEE in one of the lines coming off the VDV.

http://www.FastForwardSuperchargers.com/Problems/bypass-valve-1.jpg

[chuckerants]

Do I need to worry about this on the Hotside? If so, where would I move the bypass vacuum to?

[Tom @ Fast Forward]

Wouldn't hurt. Move it to the throttle body adaptor. Tee it into the IAC hose.

[chuckerants]

Wouldn't hurt. Move it to the throttle body adaptor. Tee it into the IAC hose.

Does it matter which of the 2 hoses going to the IAC?

[Tom @ Fast Forward]

Yes. It needs to be the one from the Throttle Body Adaptor. Not the one from the Throttle Body.

[ScottA]

Does this apply to all years of miata with your FFS kit??

[Tom @ Fast Forward]

Yes. Actually, I suggest it for all superchargers. FFS, BRP, JR.

[99mx5]

I did this mod and all works well :)

[gludlow]

I'll try this on my new install once I get everything together; looks simple.

[snakebit]

I have no free nipples on the VDB; can I tee it into the line connecting the valve cover breather to the BTB?

[Tom @ Fast Forward]

Yep. You can tee it into any line that is going or coming from the VDB. I think that the cruise control is 1/4" and might be easier to tee into as you need 1/4" for the bypass.

[snakebit]

Is that brass elbow at the end of the bypass valve vac line a single piece that screws into the manifold?

What is its diameter and thread size (so I can find a matching plug)?

Thanks!

[Tom @ Fast Forward]

1/4" NPT pipe plug. It is available at any hardware store.

[ThomS]

Tom could this be some of my random codes that I am getting or did we already correct this when you were out last year. I should be taking this out of it winter sleep soon, and I have to get it to Kenjistu Auto to put on new cat and MId pipe soon.

[Tom @ Fast Forward]

Thom,

I think your random codes are the wires that need to be cut in the harness. The two that have been done have not re-occurred. When you get it over to them, have them call me and I can tell them what to cut. Probably take them 10 minutes tops. They can swap that vacuum line too.

[Doug Dunkerley]

I was just starting to work the bugs out of my FFS last summer when my wife was diagnosed with breast cancer. Everything got dropped for the last 8 months with surgery, reahab and most of her chemo. She seems to be doing well now with a good prognosis. Got back to the 94 Miata again ast week. It would idle great but stumble, smoke, backfire and die with any throttle and still did when i started it a couple of days ago. I had orderded a freeflow SS exhaust and installed it thinking maybe the cat was blocked or too restrictive with the FFS. It didn't help. Finally I decided to check the web site to see if there was anything new. I saw this post; made the mod and presto seem to run fine now in the garage. Need to get the registation and insurance back on it for the first and long awaited road test
:party:

[Tom @ Fast Forward]

Doug, we did say a special prayer for your wife at church this morning. I pray for her complete recovery.

I'm not sure why this fix would cure tat problem? Make sure the linkage in the bypass valve is free from obstruction and turns freely.

I was just starting to work the bugs out of my FFS last summer when my wife was diagnosed with breast cancer. Everything got dropped for the last 8 months with surgery, reahab and most of her chemo. She seems to be doing well now with a good prognosis. Got back to the 94 Miata again ast week. It would idle great but stumble, smoke, backfire and die with any throttle and still did when i started it a couple of days ago. I had orderded a freeflow SS exhaust and installed it thinking maybe the cat was blocked or too restrictive with the FFS. It didn't help. Finally I decided to check the web site to see if there was anything new. I saw this post; made the mod and presto seem to run fine now in the garage. Need to get the registation and insurance back on it for the first and long awaited road test
:party:

[snakebit]

I have two close friends who are breast cancer survivors. Modern medicine is finally successfully treating this intimidating disease.:yes:

I hooked the bypass up to the cruise line and it's working great.

[MX-Drew]

I was just starting to work the bugs out of my FFS last summer when my wife was diagnosed with breast cancer. Everything got dropped for the last 8 months with surgery, reahab and most of her chemo. She seems to be doing well now with a good prognosis. Got back to the 94 Miata again ast week. It would idle great but stumble, smoke, backfire and die with any throttle and still did when i started it a couple of days ago. I had orderded a freeflow SS exhaust and installed it thinking maybe the cat was blocked or too restrictive with the FFS. It didn't help. Finally I decided to check the web site to see if there was anything new. I saw this post; made the mod and presto seem to run fine now in the garage. Need to get the registation and insurance back on it for the first and long awaited road test
:party:

Best wishes to you and your wife at this hard time. That is the great thing about the Miata / MX-5 it brings people together.

[Swingwing]

Tom,
On my 99 with the BRP/SOT kit, the IAC valve is still mounted to the throttle body, and there aren't any vacuum lines going to it. I have a couple of unused vacuum ports on the intake manifold, but won't those also see boost from the supercharger? Any suggestions?

[Tom @ Fast Forward]

Is there any port coming off of the adaptor between the throttle body and the supercharger? If so, that is where you would like to tap.

[Swingwing]

Nope, it's a solid chunk of aluminum (?)...here's a pic:

[Tom @ Fast Forward]

Well, while you have it off, drill and tap a 1/8" NPT hole in the top or bottom and install a 1/8 NPT x 1/4" barb (Ace hardware, Home Depot, etc.) and connect the 1/4 vacuum hose from the bypass to that barb. Also the perfect place to tee in for cruise control.

[Swingwing]

Good idea--unfortunately that's a picture from the instructions. If I get motivated enough, I'll take it apart and do that. I hope for my next project to be a Torsen swap.