my vacuum at idle, usually around -15, was looking like -13... ( i am at 2200 ft 13.6 BAR) i did a comp test and the motor was happy at 115. time to look for a vacuum leak. i did some searching and bought an Autoline Pro. i found zero leaks except for around the throttle plate rod bushings... mostly the front bushing. it seems to be fairly modest but i have zero experience doing the smoke thing. is there a fix? it will make little diff as to power and driveability but i don't like not seeing 15. any guidance appreciated.

share your smoke story

 

Some years back when I was smoke testing the intake ( yes everyone should be smoke testing the intake for leaks ) , I discovered a leak around the primary shaft front quad seal. I ventured into replacing it which took me down the rabbit hole. I did a write up on replacement of the five (5) quad rings that are used. You have to remember that the tb shaft sees movement every time you move the throttle pedal. That’s a lot of movement. The assembly uses bushings that support the shaft, which are peened in from the ends. The quad ring is sitting in a machined chamfer built into the bushing.

I am not sure the extent this affects the vacuum produced. When you’re smoke testing, you’re pressurizing the intake track. When the engine is running its producing vacuum. Could be more affected by vacuum than the pressure making the leak worst when running. Hard to judge. It’s like when testing ac systems. I’ve seen some not leak when under vacuum where the orifice gets pulled closed and seals but leaks when pressurized.

For what it’s worth I pull around -13 on a very large street port @980 rpm. Compression is good as well. Either way I do not accept leaks on systems that are supposed to be sealed. Here is my thread which could help. Also, JP3 is offering the TB refurbishing service now if you decide to go that route.

~GW


https://www.rx7club.com/3rd-generati...rbish-1144243/

 

wow, that's a five star thread re the rebuild of your TB. i see you have a dental pick, one of my fav tools and i use it everyday for something.

 

you can cap off the compressor inlet and use it to pressurize the turbo system (just look up a generic boost leak tester). You're not trying to "hold pressure" like on a coolant pressure test, you're just looking for leaks. Spray slightly soapy water around areas that you may be feeling air escaping, and watch for bubbles.

 

Link below directly to the seals that gdub29e used in his writeup. Was planning on replacing my own but decided to go DBW.

https://www.metricsealsinc.com/xn70m...100-q-10-x-2-5

 

yes, on the seal link.i just ordered them along w a JIS screwdriver/driver.


after considering my options and the remaining time before the Oct 12 Texas Mile i decided i didn't need any new rabbit hole projects (DBW) so elected to replace the seals in my TB. my TB is beautifully ported by Brian Cain so i am not excited about pitching it. if gdub's thread didn't exist no way would i do the rebuild.

once complete i will post my vacuum readings. hopefully the rebuild will be a help.

 

I’m glad to see that the tb refurbish thread is still helpful. As time goes on, the quad rings leaking will start to become a common issue. It’s also great that - metricsealsinc - still carries these. I was told at one point that they were phasing out metric quad rings for a standard variant.

I’ve tried out the soap and water like Raymond suggested, but it’s a lot more time consuming than the smoke option. Some people don’t have an air compressor either. I had made an adapter that attaches to the front of the turbo ( single turbo ) with an air hose attachment to pressurize the intake track. Takes awhile to hunt leaks down this way.

Now I just use the smoke method. It’s a less time consuming method and you know in short order where the leaking is. All you have to do is block off the turbo inlet on a single style with tape or even Saran Wrap along with the tailpipe. On the twins cars I found it’s easiest to block off the twins at the primary elbow tube and rear air tube. Here is a link to the “cheap” smoke testing. I just hook the hose up to the brake booster port on the uim. This way is great for the dyi guy tho I will say those smoke machines like Howard has pictured are best.


Howard, I’m not sure how your bored butterfly blades will be attached. Hopefully it’s in the same method as the factory. I will say that using a small battery powered impact driver with a jis tip comes in very handy. It alleviates any damage from hand removing the jis fasteners. I use a m12 Milwaukee. That with a heat gun and some penetrant, they zip right out of there nicely.


~ GW

 

i found my throttle body O rings at the butterfly shafts were the culprit for slightly declining vacuum. after swapping in new O rings my idle vacuum is now back to normal. thank you smoke machine and THANK YOU gdub for your really great tutorial. i probably wouldn't have taken up the task without your thread.

i did purchase the screwdriver and found that the screws were not a problem. the screwdriver does have the impact feature. it twists if you use a bit of hammer. NOT recommended. as Dale correctly posits, the TB has the ability to kill you. a sticking throttle is the last mod you want. hammering on the butterfly screws can bend the support rod so if you find the screws a bit difficult proceed very carefully. i chose to not use Loctite on the screws. i used a tiny bit of Hondabond. they won't loosen due to vibration but will still be easier to remove if necessary.

of course what job wouldn't be complete w some sort of screw up. after all was buttoned up i went for a drive. all seemed good except for a stumble on accel and no knock readings. hmm. i looked at the log and found no TPS numbers other than zero. i had incorrectly installed the outer plastic cover on the TPS. it needs to be properly clocked. when you bolt it back onto the primary aluminum body it needs to be positioned so the elec connector is straight up. you then rotate it CCwise and attach the two bolts.

overall, an easy project. my car has 110 K on it so take note re your TB. .

again, Yuge props to gdub29e for sharing how to do something that would have been a black hole for me.... making it a relatively easy job. also, love the recommended screwdriver, one of my fav tools these days.

sharp eyes might notice the JP3 bracket for my shorty throttle cable, another one of my favs.

https://jp3motorsports.com/products/...ttle-cable-kit