Serious power loss between 3.5k - 4k RPM

sgolenski

Registered User
Greetings,

I cannot remember if I asked this last summer or not...

'89 SC, bone stock, 5 speed w/ 61k miles.
I lose power between 3500 - 4000 RPM. The boost gauge starts dancing and I hear a weird air discharge sound. It's almost as if someone shuts off the supercharger. I first thought it might be a coil pack (original was replaced under warranty WAY back in the day because it did a similar thing), but that wasn't it. Any ideas where I should be looking??

Thanks!!
 
When was the last time the belts/tensioners/idlers on the jackshaft/supercharge were inspected? Is the jackshaft bearing ok?

How old are the catalytic convertors? Do you know how to check them? Are the pulses at the exhaust tips even? Looked at the plugs? How old are they and the wires?
 
Ironically, the belts were just replaced last summer and the idler & tensioners looked & felt good.

Honestly I have no idea how to check the cats other than knowing where they are... LOL! And yes the exhaust seems normal and even out back.

Is it possible the supercharger bypass is opening a bit just over 3500?
 
The bypass works/opens under vacuum. Shouldn't be any/much vacuum at that RPM, I'd think.

See this thread for discussion: http://www.sccoa.com/forums/showthr...r-butterfly-valve-stays-shut&highlight=bypass

With the engine off, observe the position of the lever on the bypass, then start the engine and confirm it moves to open it at idle, under vacuum.

A quick test of the cats is to run the car, get them hot, then check with a laser temp gun. See if they are both at similar temps, whatever that is.

How old are the plugs?

the belts were just replaced last summer and the idler & tensioners looked & felt good.
I'd confirm current status...only takes a minute ;)

Might be some info on your symptoms here: http://www.sccoa.com/forums/showthr...cks-at-boost-what-to-do-next&highlight=bypass
 
"How old are the plugs?"

To be honest, they're probably the ones from the factory... I know, I know I REALLY should change them. It just seems like a real PIA job. The older I get, the lazier I get!!

Thanks for the ideas man, I'll poke around under the hood and do some reading. Maybe I'll get this figured out.
 
Changing plugs on an SC IS a real PIA, no doubt. If that's the issue, you can only grin/bear it. Good luck.
 
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