no boost problem

SkylineGTRr32

Registered User
Hi everybody,

I have a 90 SC with the auto trans.
The vacuum actuator will not release the vacuum pressure. When that happens, theres no boost. The gauge will not go past 0. I can remove the vac line and release the pressure and it will boost for a while again. Then it locks up again.

I looked on this site for info, but could'nt find the info.


Extra info that might be relivent, The tranny slips in overdrive.

I'm trying to sell this car so I need help.

Thanks
 
Did you try popping the hood and blipping the throttle. It should move when you do. If not replace it.

Lucas tranmission anti slip did wonders for me. It wont make it run new, but it will make it driveable.
 
Mine did that when I converted to conventional brakes and didnt hook the lines up properly. You could have a stuck valve, but check the lines first.
 
I replaced the vacuum valve with another one I had. No luck. So the vacuum problem must be some where elts. I would think that the vacuum presure would leak not stick. Any ideas on where to start looking on the vacuum system?

Thanks for your help guys.
 
Does it feel like it has boost? or does the guage match the feeling of the car? Try running just one small hose from the valve to the small nipple on the lower IC tube right next to it.
 
Ya, the car has no power unless I pop the hood and take off the vacuum line to the actuater to release the vacuum. After re-attaching the vacuum line it will boost again for a little while. Then it just gets stuck again.
 
Just a thought,

My tranny started to shift realy hard just before overdrive started to slip.

Is there vacuum going to the tranny? And if so is it possible that what ever broke in the tranny is locking up the vacuum?

This is the first automatic I have ever owned. I'm a stick shift fan.
 

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No vacuum going to tranny on an AOD....it uses a cable attached to the throttle linkage.

To correct the bypass valve problem, I suggest pulling off whatever vacuum line your currently using and pluging it. Go buy a vacuum tee and tap into the cross talk vacuum hose and run a new hose from there to the bypass actuator.

Here is a picture of the hose I'm talking about tapping into.

http://i105.photobucket.com/albums/m240/shadow357x2/Picture019.jpg

And this is how it looks with the tee installed.

http://i105.photobucket.com/albums/m240/shadow357x2/DSC00037.jpg

David
 
Thank you for that advise. I will try that. Right now I have a hose going from the actuater to the intercooler pipe. So my boost gauge does not work, but my supercharger does.

The tranny must be something elts. It's just strange that it all started at the same time. I noticed that overdrive works for about 3 blocks everyday. I don't know, I miss my old 5sp SC.:(
 
David Neibert said:
No vacuum going to tranny on an AOD....it uses a cable attached to the throttle linkage.

To correct the bypass valve problem, I suggest pulling off whatever vacuum line your currently using and pluging it. Go buy a vacuum tee and tap into the cross talk vacuum hose and run a new hose from there to the bypass actuator.

Here is a picture of the hose I'm talking about tapping into.

http://i105.photobucket.com/albums/m240/shadow357x2/Picture019.jpg

And this is how it looks with the tee installed.

http://i105.photobucket.com/albums/m240/shadow357x2/DSC00037.jpg

David


Thats what cured my problem, If I rememeber right dave was the one that mentioned this bypass to me. here is the link to the thread that sounds alot like yours. for about .75 you should be able to fix it

http://www.sccoa.com/forums/showthread.php?t=79383

S
 
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