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'97 Deville engine misfire and eating spark plugs


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I have a '97 Deville D'elegance with 95k on it. The car had 81k when purchased. Since then I have replaced spark plugs & wires twice, replaced the coils once. Last week the car started to "miss" again, and yesterday the service engine soon light came on as the car was running rough. P0300 code for engine misfire as well as stall code plus two transmission codes are now present. When the plugs were replaced with AC Delco plugs at about 85,000 miles and again at about 90,000 miles some of the platinum tips were burned right off the plugs. This was the case the first time I replaced them. What is happening to shorten the plug life so dramatically? Any help would be appreciated.

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What ignition wires and coils are you using? Pull the vacuum hose on your FPR and see if you have fuel present. Are you using regular gas when premium is called for? Pre-ignition could be present. Before you got this mis, how was it running? How was the idle?

Are you sure the plugs are the correct part number, using the wrong part number could pose a heat range problem. Do you see a check engine light and what are your codes, besides the P0300?

I found this:

Signs of the spark plug being hot or blistered and/or melted center and ground electrodes are indications of initial preignition. Check that the correct heat range spark plug is being used, assure ignition timing and air fuel mixture are appropriate, assure entire ignition system is functional and check its specifications. Pay special attention to the EGR system and/or knock sensors. Routing of spark plug wires on some engines can contribute to cross induction which will lead to pre-ignition. Excessive carbon deposits in the combustion chamber may contribute as well.

Melted center and/or ground electrodes and/or a melted insulator are symptoms of sustained pre-ignition. See initial preignition, description above.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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BBF has covered the bases pretty well. It would help to have all the codes, as BBF suggests. There is one last thing to look at: how old is the air cleaner? If you have one or both of thes:

# P0171 - Fuel Trim System Lean Bank 1

# P0174 - Fuel Trim System Lean Bank 2

then you may have a clogged air cleaner. Also, make sure that the air cleaner housing is firmly seated in the fender well and the hose between the throttle body and the air cleaner is on correctly and is not kinked or dented. If the air cleaner not well seated, the engine will take in some underhood (i.e., hot) air instead of cool air from the space in front of the radiator. Any restriction in the air flow can cause the fuel injection to fail to add enough fuel to avoid a lean condition when the engine is under load, such as high speed freeway or turnpike driving.

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