2000 Bonneville SSEi shaking when hitting boost?
So I just had my mechanic do some repairs
on my car, one of them being hooking up
the belt to my supercharger. He told me the
supercharger was in good condition, but
whenever I accelerate hard enough, the car
will pick up fine until I hit boost. The car
begins to rumble/shake once the needle
hits 0 and doesn't seem like it wants to go
past 0, but it will if I stay on the gas. My
mech said that he thinks it's because the
axle is off balance because of how bad the
wheel hub bearing was that he replaced.
The car runs perfectly at freeway speeds,
the problem only shows when I push the
car into boost. Before he connected the
supercharger, I could hammer on the gas
with no issues, so I'm positive it has
something to do with the supercharger. I
read that it could be a bad coupler, but my
mechanic says the couplers are OK. The
car has 206k miles, incase that info is
useful to you. Open to all input. Thank you
for your time!
I think your supercharger is ready for a rebuild.
Thanks Mike! My mechanic told me that he took the supercharger apart and cleaned it out, and that it looked to be in good condition. I wouldn't consider it to be out of the question though. When I bought the car, the guy said he disconnected the supercharger because it was too much for his wife during the winter. He was a shady character though, so who knows why he really did it. I'm going crazy with all of the different answers I'm finding. (Bad coupler, bad plugs or wires, bad motor mount.)
To be honest, those are all plausible answers. Think about what happens when you hit boost. The engine will torque over harder (bad mounts would create a problem at that point), a significantly higher amount of air enters the engine (gaskets leaks and whatnot are more apparent), the computer drastically enriches the fuel mixture (clogged injectors and crappy plugs might not be up to the task)...and so on. A lot is happening. But if the engine runs good under some hard pulls with the SC disconnected, and then suddenly runs shitty when the SC is reattached, and the previous owner had it disconnected, not to mention these SC units aren't known for longevity, I think you know what youre looking at.
Admittedly, I don't know a great deal about that SC. But I can tell you this. Superchargers are meant to create boost from the moment you hit the gas until the cant keep up. So if theres a lag time (between initial acceleration and boost) then there must be a diverter valve in there somewhere to allow boost to be wasted (much like a wastegate on a turbo setup). So under light acceleration the valve is open and the air escapes and you don't have boost. Is the valve is stuck open, then the computer would compensate for the boost it SHOULD be seeing, and you AF mixture would be way off, causing a stumble. Then again, this could all be a bad MAP sensor, if the car has one. The MAP sensor is would would be telling the PCM you now have boost, and the PCM in turn enriches the mixture. If the MAP sensor is faulty, the PCM may never know you have entered boost and therefore no enrichment takes place and youre running super lean, causing a misfire. Again, this is just basic theory and Ive only really worked on this engine once, and it wasn't SC related. So don't quote me on this. These are just possibilities.
Wow Mike, this is a lot of info! Thanks! I'm hoping that this is just a mixture of small fixes and not gonna be some tremendously costful repair. I know very little about cars in this aspect.
Here check the pic out. Your supercharger has a bypass valve. Check the valve, actuator, hoses and boost controller.
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