Need help! Boost comes in too quick! how do I fix?

flynbrd

Registered User
Since I modified my motor the boost comes in quick. With only a little throttle my vaccuum goes away and here comes the boost. Depending on the amount of throttle I usually see a few pounds. I was told that I need to put a small vaccuum line on so the controler gets a better signal? Where is this line on my 1990 t-bird? Could I use a valve to restrict the signal? Btw there are no vaccuum leak on my motor also I put a check valve in for the cross talk line.

Thanks
John
 
boost comes on to quick

Couple of questions. Are you using a overdrive pulley? Do you have exhaust work done? The excessive boost could be coming from to restrictive an exhaust system. A good way to blow head gaskets.
 
at times I wish it was turbo

The car has everything done to it except magnum intake and tb and pullies. How can I bypass the control unit? Connect a three way t? Side one to the supercharger inlet, side two to the bypass valve, side three to the manifold inlet? ANy harm in doing so? Also due to the nature of the bypass valve could I not hook a small spring to it? The spring would assist the strength of the vaccuum and in theory change how fast it opens and closes?
 
boost comes on to quick

The real question is do you have a restriction that is causing tne boost to come on to quick or go to high. I have never heard of making the boost come on slower. A late model pulley will slow down the blower, which in turn make it come on later. Do you have exhaust mods? If you have a built motor with stock exhaust that is probably your problem. To much restriction will cause the boost to go really high.
 
yes

Embree Blower
2 1/2 exhaust, sccoa headers
stage two cam
port intake and heads
custom intercooler
etc.
 
With only a little throttle my vaccuum goes away and here comes the boost.

And that is a bad thing becuase.............. :confused:

The point of modifying your car is to make it faster. Well, the faster you get into boost, the faster your car is going to be. I certianly wouldn't see this as a problem.

Thomas
 
With only a little throttle my vaccuum goes away and here comes the boost. also I put a check valve in for the cross talk line.

That's the problem...remove the check valve and it won't be as sensitive. That's exactaly why I put the cross talk tube back on, it got very annoying engauging the supercharger whenever the slightest load was applied to the engine.

David
 
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Need help boost comes on to quick

The problem is if the boost is coming on real quick or going high it may be a sign of to much exhaust restriction. As anyone can tell to much restriction in the exhaust is probably the number one cause of headgasket faliure. And that is a bad thing.
 
How?

"That's the problem...remove the check valve and it won't be as sensitive. That's exactaly why I put the cross talk tube back on, it got very annoying engauging the supercharger whenever the slightest load was applied to the engine."

David how would it affect the boost sensativity? The check valve prevents boost from going back into the TB side. Normally the talk tube allows about 1 pound to blow by, but with the check valve in place this prevents that and still allows for vacuum. Does the check valve restrict the vacuum signal that much? Also there is a posting called throttle body brands that has a pic posted of the driver vacuum tree. Can you name that vacuum line :)

Thanks
John
 
With the way our blowers are designed, there shouldn't be anyway that boost could get back into the TB.

Thomas
 
In my 95 before I stopped driving it and modded it all crazy, Maybe because it was a five speed, boost always came in rather quickly. Even if I drove like a granny, shifted all easy, i'd still hit 2-4 psi of boost. My 90xr7 never did anything like that. You really had to work it to get the boost going. Now on my 95, since it's recently living again, after I attached the front portion of the xhaust, I gave her a good rev, to about 4000rpm, and hit 5psi boost at idle. Go figure, every car is different. My cougar even had my tb/maf/9in k&n from the bird, and mufflers removed, and still I had to work it for boost.
 
David how would it affect the boost sensativity?

John,

I don't know why or how...but it does. Pull the entire hose off check valve and all, and install another hose of similar size and see if the problem goes away.

BTW, I didn't loose enough boost to even notice it on the gauge.

David
 
I think its used more as a pressure bleed than anything else. Ya know.. to kinda take the edge off the boost spike and smooth out the transistion to boost.;)
 
I made the bypass vacuum system with no noticable effect.. Its still the same, I switched a restricted vacuum line from tb side to the inlet side with no really difference. I'll remove the check valve but I feel that it wont change anything.
 
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