Boost leak or possible issue?

1FSTBRD

Registered User
I'd used the search function to research why boost would be a bit lower than it should--check all vacuum lines, hoses, connection, cracked/ failing rubber hoses, boost gauge line in case it is sending a false reading, etc. Anyways, when I got my SC a few months ago, when you'd pin the gas pedal, it would hit 12 psi, which is what it should be at. Now, at some point, it's hitting about 9.5 to about 10, and I've ruled out the boost gauge, because the car does feel noticeably slower.....it would roast the near balding tires, now it still spins, but not as violently.

I'd put in a double intercooler yesterday, and this is how I'd noticed the boost being lower. Thinking that it may have been a leaky DIC, I put the factory original back on and it was still reading lower. Now, I hadn't checked the boost gauge before I'd done any of these intercooler swaps, but thinking back to it, about maybe 3-4 weeks ago was when the car felt like it had lost a gear or so. I had someone else in the car and the car was slower, but I had the A/C on, so I thought that between the passenger and A/C drawing power, that it was the reason that the car was slower.

I've also checked all the intercooler connections--at the blower, the upper tube, lower tube, etc. All good, because I'd sprayed it with carb cleaner.

The boost actuator solenoid thing, that is working well and freely and it's not stuck or anything.

I'd noticed that my belt isn't as tight from the crankshaft to the jackshaft, and it's just a little bit tighter on the supercharger belt. The jackshaft/ crankshaft belt has much more play in it than the accessory belt. Could this be a reason why it's getting less boost? Also, I'm not sure when the spark plugs were last changed--could a misfire or something like that have any affect on the boost, too? I'm thinking that it could be a tensioner, as well.

Also, the exhaust sounds louder. I may have an exhaust leak. Could this also be a reason why? With less backpressure with an exhaust leak, I'm thinking that it may have some effect on it.
 
I'd put in a double intercooler yesterday, and this is how I'd noticed the boost being lower.

Which could be a reason for a slight drop since boost is actually a measure of backpressure, and the dic would 'add' a slight drop.

Also note that spraying with carb cleaner is not advised on our cars where the EEC will compensate faster than you can notice any change.

Instead, I've used the method where compressed air is pumped into the intake with the engine off, with good results.
 
Which could be a reason for a slight drop since boost is actually a measure of backpressure, and the dic would 'add' a slight drop.

Also note that spraying with carb cleaner is not advised on our cars where the EEC will compensate faster than you can notice any change.

Instead, I've used the method where compressed air is pumped into the intake with the engine off, with good results.

I should have mentioned that I'd put the original IC back on the car......trying to troubleshoot it so that it would rule out the intercoolers. It's still at 9.5 to 10 or so PSI.

I'd done an el cheapo smoke test, by taking a cigar and blowing smoke through the intake---it didn't leak out anywhere.

Good to know with the carb cleaner with these engines. With compressed air, could I just take my tire compressor and rig up a some sort of nozzle or end that would blow the air through?

Of note, someone had removed the cats on the car before I'd bought it. But the engine was still pushing 12 psi, as I'd gunned it a few times right after I bought it, and it was holding 12 psi.

Doesn't appear to be an issue with the dreaded headgaskets, because the vacuum in the engine is still where it should be, and there's no white smoke.
 
Sounds like it may just be the summer heat you are experiencing. Hotter less dense air makes less boost and less power. Not unusual to gain 2 pounds of boost in cooler weather, or lose it in hot weather.

Second most likely cause is belt slip, from either the JS to crank pulley or the supercharger to jack shaft pulley. Usually slips worse on the JS pulley to supercharger belt. Adding a set of stronger tensioner springs and fresh belts (Gates) is usually all it takes.

David
 
Sounds like it may just be the summer heat you are experiencing. Hotter less dense air makes less boost and less power. Not unusual to gain 2 pounds of boost in cooler weather, or lose it in hot weather.

Second most likely cause is belt slip, from either the JS to crank pulley or the supercharger to jack shaft pulley. Usually slips worse on the JS pulley to supercharger belt. Adding a set of stronger tensioner springs and fresh belts (Gates) is usually all it takes.

David

Thanks, David! Yeah, I was wondering if it wasn't the hotter weather, too.
 
I'd got new jackshaft and supercharger belts.....man, were they tough to find! There was only basically one of each in the city, among many stores. When I took a better look at the tensioners, it looks like they are shot. I'm assuming that if the tensioners are shot, it wouldn't send the correct amount of boost, since the belt/ tensioner isn't rigid enough to hold that type of load, essentially slipping? Is this a correct assumption?
 
Yes, loose/worn belts can slip.

Tensioners have wear indicators on the face to indicate range left/used. What do yours look like?
 
Yes, loose/worn belts can slip.

Tensioners have wear indicators on the face to indicate range left/used. What do yours look like?

What do mine look like? Ha ha.....the pointer is not even registering on the indicator field. The main accessory belt is about at the halfway mark. I'm lucky that these didn't slip off at some point, so I guess there's something to be said for the maintenance side of things. :D

I'll have to call around tomorrow to find the jackshaft and supercharger tensioners.
 
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