Losing boost after 3300 RPM

leeklimala

Registered User
The title says it all. When getting on the onramp this morning I noticed that before I was letting off the gas to switch gears I was losing boost. Upon some more A$$ dyno-ing down the highway, I was getting a full 15 psi at WOT but as I passed 3300 RPM the BOOST would just drop away as the RPM's rose. What does this mean?
 
I am having trouble picturing this. It would seem from your post that your blower is worn out and can not keep up with boost as the rpm grows. I would assume that you have already checked for leaks at the IC/top and that the valve is functioning properly. I believe it is bleeding at that speed but you might want to test your guage to be sure you do not have a loose connection.

Chris
 
Lee, how old is the belt? If it's not sliping, I'd do a fuel pressure check. I've got a pressure tester gauge kit if you want to borrow it.
 
Looking at your members page ... the only mods you have listed are "Homegrown Cold Air Intake" and "Flowmaster Exhaust". If this is correct, how are you possibly getting 15 psi of boost in the first place?
 
XR7inWI said:
Looking at your members page ... the only mods you have listed are "Homegrown Cold Air Intake" and "Flowmaster Exhaust". If this is correct, how are you possibly getting 15 psi of boost in the first place?

Just going off the factory guage. At WOT it will peg it.

I do have alot of black dust on the front nose of the SC, and a bunch of motor oil leaking from the top. Could bad plastic tensioner pullies cause slippage? I do know I need to replace them. What else should I check as far as slippage goes?
 
UPDATE: Losing Boost at 3300 RPM

Today I checked my belt again for slippage and found about 10X more black dust on the SC snout, all my plastic pullies are shot but I can't see where the belt is being worn down at?

Also, my boost guage was acting sluggish on the way home. It would charge up, stick then suck back down, then when I'd accelerate again it would take a second or two then jump up into the boost range. when I got home the connection was good at the manifold. Any takers?

General engine tech part:

Here comes the fun part. My oil pressure dropped far enough to turn the light on, when I checked the oil when I got home the dang dipstick was smoking. The oil was actually high, which I don't understand b/c of the amount leaking out of the SC top and whenever the boost guage line comes off oil is sprayed onto the firewall. The oil pressure sending unit is only 2 years old. There was also a funny smell to the oil. The oil is only 1500 to 2000 miles old. No shavings in it either. Can't think of anything else.
 
Belt is slipping. The collar nut is loose, that is why you are getting oil blwoing past it. Check/replace your PCV valve.

Dave
 
Big Cat Davo said:
Belt is slipping. The collar nut is loose, that is why you are getting oil blwoing past it. Check/replace your PCV valve.

Dave

Colar nut has never been removed. Oil coming from the SC top base. That has been removed and resealed with copper gold spray 2x. I've heard I need to go with the orange RTV??? How do I fix belt slip? Do the tensioners go bad? Or is it just b/c of my factory plastic pullies going bad?
 
It could be your tentioner pullies, but I don't think so....

You installed a 10% pulley on you SC and maybe the tentioner just can't take up the slack anymore.....

A new tentioner with a larger pulley might help with this situation.....

Or you could go with 5% JS and 5% blower pullies..... :D
 
I use Loctite Anerobic sealer that is what the Eaton uses at the factory and is by far the best stuff to use. Good/Year gaterback belts are also the best belt to use on the SC/Napa being the worst i have ever used. If the plastic pulleys are not round they can send harmonics (bounce) threw the belt making it loose conntact with the pulleys. Yes tensioners do need replaced sometimes. There is a friction plate inside to help reduce belt bounce, if yours feels very springy then look into replacments. Since you are going into WOT but have little/no boost you might be flooding the motor. It is possible that you are getting alot of fuel into the oil from washing down the cylinder walls. That might be a bit of a stretch but i have seen it before with tuned cars.
 
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