Vac leak at throttle body spring

Condor232

Registered User
I just smoke tested the car and I have a pretty big leak coming from the spring/seal area where the throttle cable turns the throttle plate. Is this area subject to vacuum? My gauge is telling me I have a large leak but I haven't been able to locate any besides this.
 
I'll let some one more intelligent than I speak to it, but I know that I have battled an issue with idle speed control that was directly related to air leaking past the throttle plate shaft from bad end seals on the shaft. What I'm not sure of is if the seals work properly, will they seal under vac, but not seal under pressure.

I.e. pressure testing /smoke testing doesn't necessarily work, but once the assembly is under any vacuum, the seals tighten up and prevent air moving around them.
 
I smoke checked mine and it leaked through throttle blade shaft near the return spring aswell. Also at the bypass linkage too. From what I was told there is not much u can do about it. I put a new larger tb on but have not smoked it yet to see if it leaks.
I just smoke tested the car and I have a pretty big leak coming from the spring/seal area where the throttle cable turns the throttle plate. Is this area subject to vacuum? My gauge is telling me I have a large leak but I haven't been able to locate any besides this.
 
What mods do you have? CAm? I doubt the shaft would cause that bad of a leak if your cam is stock. Have you rebuilt latley?

Poor valve sealing or worn out motor could be a issue if you can't find a leak.
 
What mods do you have? CAm? I doubt the shaft would cause that bad of a leak if your cam is stock. Have you rebuilt latley?

Poor valve sealing or worn out motor could be a issue if you can't find a leak.

The motor is brand new, has less than 100 miles on it. Its a 4.3L stroker bored .050 over, with a 224/230 cam. So definitely not stock. It was making higher vacuum for the first 30 miles or so, and now at idle I sit right below -10 on the gauge.
 
there are so many other things that you would want to check first. my throttle shaft was leaking so bad I couldn't hold any pressure when pressurizing the intake tract. Most don't leak anywhere near that bad. And before I got to that point I pressure tested each piece of the entire system before calling it the throttle body.
 
What was it for the first 30 miles? Did you check the lifter preload? When I put a cam in my car I didn't check the lifter preload and it was hanging one of the valves open in #4. Car ran fine WOT but at idle it was like a big block with a monster cam and very low vacuum. It sounded sweet and would rock you quite nice, I kinda miss it.

When I did a compression test the cylinder was dead. So maybe you can start with a compression test. The lifter may have pumped up and is now hanging a valve open on you.
 
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What was it for the first 30 miles? Did you check the lifter preload? When I put a cam in my car I didn't check the lifter preload and it was hanging one of the valves open in #4. Car ran fine WOT but at idle it was like a big block with a monster cam and very low vacuum. It sounded sweet and would rock you quite nice, I kinda miss it.

When I did a compression test the cylinder was dead. So maybe you can start with a compression test. The lifter may have pumped up and is now hanging a valve open on you.

For the first 30 miles or so it was sitting at around -16. Sometimes during the drive, while sitting at a stoplight, I'll be at almost 0.

I did not check lifter preload, so that is a possibility. Although, I still lean towards vacuum because the car sometimes will die when I put it in reverse. Or if I start it after its been running for awhile, I need to give it some gas to keep it running.
 
The motor is brand new, has less than 100 miles on it. Its a 4.3L stroker bored .050 over, with a 224/230 cam. So definitely not stock. It was making higher vacuum for the first 30 miles or so, and now at idle I sit right below -10 on the gauge.

I've got a similar cam and I'm only getting around 10 or 11 inches of vacuum at 1000 rpm idle. If you were getting 16 inhces and it suddenly dropped to 10, I'm betting it was because it was idling higher than it is now. What rpms is your idle set at ?

David
 
I've got a similar cam and I'm only getting around 10 or 11 inches of vacuum at 1000 rpm idle. If you were getting 16 inhces and it suddenly dropped to 10, I'm betting it was because it was idling higher than it is now. What rpms is your idle set at ?

David

Dave,

Thanks for chiming in. I idle consistently at about 800-850. This is good to know though that you have a similar vac condition.

The only thing that I question is sometimes I will be sitting at a light and my vac gauge will read close to 0. This hasn't happened for a few days, so maybe I just need to drive it around some more to see if I can recreate this situation.
 
Dave,

Thanks for chiming in. I idle consistently at about 800-850. This is good to know though that you have a similar vac condition.

The only thing that I question is sometimes I will be sitting at a light and my vac gauge will read close to 0. This hasn't happened for a few days, so maybe I just need to drive it around some more to see if I can recreate this situation.

I think the Zero vacuum thing is just the gauge sticking. I'd suggest increasing your idle to 1000 rpms and you should get rid of the ocassional stalling problem. The guage on my turbo car is starting to stick at various readings and the same thing happened with my 91 last year.

I think mine got fouled up from years of using methanol injection. Nitrous will also cause them to foul up, because both are highly corrosive.

David
 
I think the Zero vacuum thing is just the gauge sticking. I'd suggest increasing your idle to 1000 rpms and you should get rid of the ocassional stalling problem. The guage on my turbo car is starting to stick at various readings and the same thing happened with my 91 last year.

I think mine got fouled up from years of using methanol injection. Nitrous will also cause them to foul up, because both are highly corrosive.

David

Cool, I'll try increasing the idle. The gauge is an aftermarket Autometer full sweep electric, so not sure if it would be prone to sticking.
 
DN

There's a mix for the water meth./ nitrous that deters the corrosion.

By memory I think it was made by VP Racing.

I will check tomorrow. Hopefully its still available.

What I have is 20+ yrs old, but you only use a cap per 2 gallons.

I'd heard that any nick in the zinc coating will start the breakdown.

With aluminum the results are more progressive.

Paul
 
I took the car out for about 30 minutes of driving yesterday. I observed that it was pulling about 10-11 inches at idle, and about 9 when shifted into drive. I can get into about 5 pounds of boost relatively easy, but I have not observed the gauge reading 0 since a few weeks back. I am yet to really "get on it" with the new motor, as it has only about 100 miles on it.

Sound normal?
 
I took the car out for about 30 minutes of driving yesterday. I observed that it was pulling about 10-11 inches at idle, and about 9 when shifted into drive. I can get into about 5 pounds of boost relatively easy, but I have not observed the gauge reading 0 since a few weeks back. I am yet to really "get on it" with the new motor, as it has only about 100 miles on it.

Sound normal?

Yes, it does sound normal.

BTW...If your car is 89-92 the brakes will work fine with low vacuum, but if it's a 93-95 the brakes are more dependent on vacuum and they won't work very well without adding another vacuum cansiter.

David
 
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Yes, it does sound normal.

BTW...If your car is 89-92 the brakes will work fine with low vacuum, but if it's a 93-95 the brakes are more dependent on vacuum and they won't work very well without adding another vacuum cansiter.

David

Its a 98 Mustang with a 94 SC motor. The brakes are spongy, I am assuming this is why cause I bled them 3 times!
 
The brakes are spongy, I am assuming this is why cause I bled them 3 times!

spongy means you need to bleed them the right way, again. What you will notice with the supercharged motor regarding brakes is lack of assist, particularly during or after an extended full boost adventure. I.e. burnout box just before staging.
 
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