1997 Pontiac Grand Prix GTP 3.8 Supercharged, no mods....?

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Scott T

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I have a 97 GTP that will misfire when the supercharger is at about half boost and above. I noticed the other day that after giving it a good run, the header pipes were glowing red. Back pressure test showed no problem with the exhaust and the code is a P0300 Random/Multiple misfire.....any suggestions? Could the supercharger being going out or could have a lower octane fuel like 87 cause this, I always use premium, but you never know what they put in those tanks....any help would be appreciated. PS I have done everything with plugs, wires and coil packs.....all checked out ok.
 
I'm curious about your testing for backpressure. What kind of reading did you get and how did you go about getting it? there is a huge problem with W-car converters plugging up. I know, Delphi supplies the converters for that platform to GM and I work for Delphi. The spec in the service manual is 1.25psi @ 2,500 rpm. Do this by removing the front O2 sensor and replacing it with a M8x1.5 plug drilled and tapped for a 1/8" NPT fitting connected to a line and a gauge. When the converters plug up on these cars, they usually exhibit a loss in performance and a flashing check engine light for a catalyst damaging misfire and random misfire code P0300. The other common problem with these supercharged engines is the fuel pump resisitor. If you do not have a restricted exhaust, I would replace the fuel pump resistor available only through gm dealer, part number 88951182, list price $54.
 
It sounds to me like you are running lean making the engine run really hot. Make sure you never go heavy on it with this problem or you can experience detonation and damage your whole engine. Most common cause is not getting enough fuel for the amount of air you have. The octane could make a difference but I don't think it would be that significant. That's easy to test with your next fill up though, just use premium and see if it corrcts it. If it still does it, check your fuel pressure to make sure you are getting enough pressure to provide the fuel you need. Also, check your timing to make sure it didn't advance. You might also want to go to a tuning shop to test out your air/fuel ratio just to make sure. Good luck. Don't make my mistake and ignore it, you will blow your engine . . like I did : (
 
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