XJ XJ8 / XJR ( X308 ) 1997 - 2003

Supercharger, inconsistant performance

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Old 02-18-2013, 06:58 PM
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Default Supercharger, inconsistant performance

2000 VDP, 4.0, 109,000....ok, this seems weird to me. I've been around SC's before, you mash the peddle, it provides mass air to the cylinders and the car goes like a bat outta there. So, since we're talking about a 4,000 lb car, it goes faster than a 4,000 lb car without one....theoretically.
Mine was barn burner the first few years I had her, used to eat Lexus'. Now, its like stepping in pudding. Its stock, I replaced the air intake seal and trim ring to the grooved one a few years back. So I have come to two possibilities, either the belt is slipping under power and I'm losing boost or its an electrical application that isn't applying itself properly. I could very well be wrong, but I am in trust that y'all can shed some light on this for me???

I can turn a wrench, rebuilt the front end, ..built my own collapsible front spring kit for $15 and redid the bearings, bushings, pins, shocks, ball joints etc.
Appreciate y'all's responses.....
 
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Old 02-18-2013, 07:03 PM
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possible bypass valve is stuck open / closed ?
 
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Old 02-18-2013, 07:09 PM
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I switched to the gator bite belt, but that was after a pulley upgrade
 
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Old 02-18-2013, 07:10 PM
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Ya' know, its some of the simplest things you overlook that can be seen by others. Its does sound like an open bypass valve Roger, thanks, I'll check it out in a couple days when I get home.
I will take others suggestions still if you have them ...just in case.
 
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Old 02-18-2013, 07:36 PM
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To add to this, if its simply a stuck bypass, can I use standard cleaners to free it up or is this specially coated and I need to be cautious?
 
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Old 02-18-2013, 09:49 PM
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Do you hear *any* ping? Could be a secondary fuel pump gone bad. You will run lean and the ecm will cut advance or ignition as required to protect the engine. The ecm can only detect a bad fuel pump relay, not a bad fuel pump.
 
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Old 02-19-2013, 04:38 AM
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No, haven't heard any pings, just sluggish performance.
 
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Old 02-19-2013, 05:52 AM
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I agree with Roger77 that the bypass valve is a good place to start. It is really hidden by the intercoolers so a small mirror will help to see the linkage and the vacuum hose connections. Also check the vacuum hose from the supercharger to the fuel presssure regulator - I found mine was kinked and closed off
 
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