Random misfire on a 1998 Cadillac Deville with flashing "Check Engine Soon" light on/off

Hey Scotty,

I have been noticing my 1998 Cadillac Deville (Northstar engine) to misfire at different driving intervals. My "Check Engine Soon" light will blink for 20-30 seconds and then turn solid. I noticed this issue to happen during certain speeds, which would cause my car to back/misfire, then settle back and drive within perfect parameters once I reach 55-60 MPH and no longer have any issues. As I pointed out the Check Engine Soon light does not constantly stay blinking which makes me wonder what is going on with it. I do not have an OBD scanner and worry about the cost of diagnosing + repairing the issue. I bought the car from an older couple who rarely drove it so it has relatively low mileage (110,000). I suspect that the spark plugs may be the issue, however am uncertain about vacuum leaks or fuel related issues. Have you experienced a similar situation that might help me troubleshoot my issue? Is it common to have a Check Engine Soon light to flash occasionally but not constant? Here's some more info about the vehicle: 1) I know it has an issue with passenger side air-ride suspension... small leak. 2) The fill tube has a small crack in it that causes gas to spill out when I fill it to fast (therefore I have to pump and let off, pump and let off, etc.). 3) My front blowers have stopped blowing through heat, but will blow through A/C with no problem. Heat only comes through defrost and floor vents. 4) Check engine soon light is constantly on due to a P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1) , which has been looked at by a mechanic. Was told this is due to a charcoal canister and an optional replacement that should not negatively affect my car, but however cause my exhaust to be more rich. I have not fixed this issue because Cadillac has informed me that it would cost about $750, which is money I do not have. Well that is all the information and I look forward to hearing your thoughts on the "flashing" check engine light and on at least #3 for the additional information. Maybe my issue has something to do with a disturbance to multiple issues my car is currently having, hence the term "two birds with one stone". Thank you for your time! ~ Eric

Comments (1)
No. 1-1


cat will show bad data when engine runs poorly and changing the cat will not fix an underlying problem like that. But that 20 year old caddie, sounds like it's time to say goodbye. if you can't afford 750, you should get rid of the car, odds are it needs a LOT more than that to fix it all