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Old 04-19-2011, 02:16 AM   #1
gtpmaddi
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1998 grand prix GTP 3.8L V6 supercharged, random misfire

1998 Grand Prix GTP supercharged. Random misfire on cylinder 3 seems to only happen when accelerating through 3000 RPM's... If the supercharger kicks in before it hits 3000 Rpm's then no misfire at all and full boost. If not, car engine seems to shake a little and the SES light flashes. When this happens the boost gauge shows full boost, but little occurs and car has basically no power when this misfire happens. Used a code reader and it confirmed random misfire cylinder 3 only as well as traction control being stuck off. When I tried to look for the issue under the hood, found that the belt has been a bit chewed up (but only in one section) and the silver coil packs ignition header is corroded (only the header connecting to cylinder 3). Any help or advice that could shed a light on this misfire's cause would be greatly appreciated !
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Old 04-19-2011, 10:37 AM   #2
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Re: 1998 grand prix GTP 3.8L V6 supercharged, random misfire

Welcome to AF!!

There are several possible issues here. First, how long since the plug wires were changed? Second, because the fuel pump kicks into high when the supercharger kicks in and increases fuel pressure there may be a problem with the injector on that cylinder. I would also do a compression check on that particular cylinder to see if you have a valve issue. I hope this helps with pinpointing the problem. If not post again and we can try something else.
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Old 04-19-2011, 08:16 PM   #3
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Re: 1998 grand prix GTP 3.8L V6 supercharged, random misfire

Plugs and wires is a good place to start. You mention the silver tip on the coil is corroded, that can cause the misfire too. Use a brass brush and give it a good clean, if the wires haven't been changed for a long time replace them too...

If the belt is chewed replace it too, it may be getting weak and a broken belt is something you don't want as it can happen while coasting and you might not notice it since you don't look at the instrument cluster all the time when you're driving...

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