PDA

View Full Version : Boost falling off sharply



Miller
07-11-2010, 12:26 PM
As always my car never works properly for more then a week at a time.. This week its boost falling off veeeeery fast. it used to be at 21psi. Now it goes to about 13psi and falls off consistently until about 4psi when it shifts. So the faster i spin it the less boost.. My vac hasnt changed, Iv checked all the IC tubes for leaks several times and everything appears tight. I hear no boost leaks which i would expect at the rate its leaking out. iv also pulled manually opperated the bypass and it seems to be doing its job...

any ideas what I should be looking at ?

David Neibert
07-11-2010, 12:50 PM
As always my car never works properly for more then a week at a time.. This week its boost falling off veeeeery fast. it used to be at 21psi. Now it goes to about 13psi and falls off consistently until about 4psi when it shifts. So the faster i spin it the less boost.. My vac hasnt changed, Iv checked all the IC tubes for leaks several times and everything appears tight. I hear no boost leaks which i would expect at the rate its leaking out. iv also pulled manually opperated the bypass and it seems to be doing its job...

any ideas what I should be looking at ?

Sounds like one or both of the supercharger belts are slipping.

David

Miller
07-11-2010, 10:51 PM
I thought that too.. I have the MP springs in there and both seem tight...Maybe i will try somebodys blower tensioner....

David Neibert
07-11-2010, 10:56 PM
I thought that too.. I have the MP springs in there and both seem tight...Maybe i will try somebodys blower tensioner....

How are you overdriving the blower (crank, JS and blower pulley OD percentage ?) What brand of belts are you using and how old are they ?

David

Tony8470
07-12-2010, 03:44 AM
It sounds like you have an automatic? On my previous sc the throttle valve cable came loose and had similar symptoms. Wouldn't shift when I punched it. If there's problems with the valve it can ruin a transmission in no time.

Miller
07-12-2010, 12:01 PM
its od'd w the smaller pulley and a 5% i belive.. the belt dosent seem that old but i didnt buy it so idk for sure. it never ( seemed to ) slipped befor its an all of a sudden thing like something let go.

as far as the TV cable coming off.. i have a 94 - cable..
It does seem to fall off like an extreme belt slip, and the blower dosent really get anywhere near as loud as it had I see no wear on the belts and no dust from the belt.... Iv pulled belt off and it still spins freely

89_nitemare_sc
07-12-2010, 03:25 PM
I've got the same problem.
Except my SC is stock.
I've got it narrowed down to the tensioner on the blower belt.
I notice the fall off of power at 2500 rpms and hits a whopping 4 psi at 3k when I kick the clutch and shift. :( no power shifts.

Anybody got an idea of where to find one, and how much of a pain a tensioner is going to be?

Thanks

DrFishbone
07-12-2010, 03:39 PM
I've got the same problem.
Except my SC is stock.
I've got it narrowed down to the tensioner on the blower belt.
I notice the fall off of power at 2500 rpms and hits a whopping 4 psi at 3k when I kick the clutch and shift. :( no power shifts.

Anybody got an idea of where to find one, and how much of a pain a tensioner is going to be?

Thanks

You can get stiffer springs at Magnum Powers (http://www.magnumpowers.com/thunder_pro_pri.php)....that should help reduce or eliminate belt slip.

90blkbrd
07-12-2010, 03:42 PM
I would check the vacuum lines on the bottom of your Inlet(assuming yours is built like mine). You can't see them and starter fluid didn't help me find my leak under there.


I've got the same problem.
Except my SC is stock.
I've got it narrowed down to the tensioner on the blower belt.
I notice the fall off of power at 2500 rpms and hits a whopping 4 psi at 3k when I kick the clutch and shift. :( no power shifts.

Anybody got an idea of where to find one, and how much of a pain a tensioner is going to be?

Thanks

I'm sure you have a vacuum leak and should start your own thread so people can help you with your problems.

David Neibert
07-12-2010, 04:01 PM
its od'd w the smaller pulley and a 5% i belive.. the belt dosent seem that old but i didnt buy it so idk for sure. it never ( seemed to ) slipped befor its an all of a sudden thing like something let go.

as far as the TV cable coming off.. i have a 94 - cable..
It does seem to fall off like an extreme belt slip, and the blower dosent really get anywhere near as loud as it had I see no wear on the belts and no dust from the belt.... Iv pulled belt off and it still spins freely

Check the bypass valve linkage on the back of the supercharger to make sure it's not sticking open partially.

David

XxSlowpokexX
07-12-2010, 05:03 PM
I told him the bypass. Makes most sence to me

Miller
07-12-2010, 06:27 PM
well after i checked bypass and found it was fine, and after i rechecked all the couplings and found fine.... I stuffed a piece of wood on my gas pedal n found the throttle only opened like 25%.. theeeeeeen i knoticed the bottom bolt on throttle body bracket came loose and when i hit the pedal it pulled it backwards n then returned to its place...i put a bolt w a nut on it and its back to normal ;)

duhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

shoalcracker
07-12-2010, 07:45 PM
Cheapest 25 HP I've seen yet.

Miller
07-12-2010, 08:11 PM
Cheapest 25 HP I've seen yet.

it gave me alot more then that ;)