Paul 5/7/2010

1998 Mercury Grand Marquis LS 8Cyl4.6L - Engine

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any ideas whats causing pre ignition

pre-ignition, ambient temp 80 deg.+, 30mph up, cruising, level ground.
Mash gas pedal, clatter increases for split second and quits.
Does not happen in cooler weather.
EGR syst. OK
87 or 93 octane, no difference.
Air filter cln.
Plugs 20k mi.
oil chng, 3 - 5 k mi.
Drive 90 mi./day, all hwy. 55 - 85 mph

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  MOONSTER_TOOLZ 10/15/2010

  Did you check ignition timing if correct? Check for over-advance ignition timing. Also it is a possibility that your EGR valve is stuck closed and your compression ratio in the combustion chamber is high. Moreover a defective knock sensor can also be the cause. Have you done with scan tool service? If not, I recommend having your engine scanned to retrieve trouble codes stored in your computer.

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