: 1999 STS V8 Northstar Engine Misfire / Smoke

06-11-10, 10:32 PM

I looked at a 99 STS tonight with the V8 Northstar in it. The guy is selling it for $900! But it does have some engine problems. He says he was out driving one day and it stalled out on him. He was able to get it back home but it had started misfiring after the stall.

He also mentioned that there was an oil leak and he had been putting in about 2 quarts of oil every couple of weeks.

He had a guy come out with a computer and the car was giving the misfire code (he did not say what the actual code was).

The body and interior are immaculate. I would like to purchase the car but I would like a rough idea of whats wrong with it and how much it could cost to fix it before I buy.

Am I looking at a complete engine replacement here, or something less severe?

Thanks for any help you guys can give. I am going out with a mechanic tomorrow but would like an idea beforehand.

Thanks again,

Mark C
06-12-10, 08:29 AM
Could be as simple as a bad ignition coil, ICM, a bad wire or spark plug, up to bent valves. If you can figure out what cylinder is misfiring and get the oportunity, just swap that ignition coil with another one on the ICM and see if the misfire moves to the new cylinder. A new coil is about 30 bucks.

06-12-10, 10:01 AM
Know that the 1999 Northstar is statistically the worst year for blown head gaskets due to cylinder block bolt hole corrosion/failure.

IF you need a new engine or extensive work on the 1999, the repair cost alone will put you in a mint 2000-2001 STS.

Missing, smoke, shakes, oil leaks = WALK, and fast.

YOU can read the trouble Codes on any 90's - 2004 Cadillac all by yourself - study the thread at the top of this Northstar main page titled "How to pull codes". Print the page and carry it with you.

Also, look at the "VIN to RPO converter" in the top threads of the Seville and Deville pages - enter any car's VIN and you're taken to a list of what's built into THAT car. (The car will not be rare - that's triggered by hidden line sequence codes).