Misfire - Please Help!
 

I have a modded 96 Cobra with a dual 77mm BBK Throttle Body and a Vortec Supercharger running 9# of boost.

Complete info on the car here: http://www.ariakristen.com/cobra/

I'm having problems with a misfire (for the 2nd time).

I recently had this problem and first tried the spark plugs because they had never been changed and were nasty anyway. The problem did not go away so I had a mechanic help me. He found a leak in the supercharger's plumbing - problem fixed. That was just a few weeks ago.

Yesturday the problem returned.

Engine is running rough (sounds just like a misfire - I assume it is)
The car has been smoking a lot on start-up (for the past couple months)
I go through a quart of synthetic Mobile 1 10W-30 every 200 miles or so
Oil is dark only 1000 miles after oil change

I checked the air plumbing for the supercharger and found no leaks or cracks. I tightened the heck out of everthing anyway. I've had the suggestion that it could be an O2 sensor, but I wanted more info before purchasing new ones so that I don't waste my money.

The car as 65K miles on it and the engine has never been taken apart. No forged pistons or any fun stuff like that.

Few questions in return:

1. What color is the smoke on startup? White or Black?
2. This may be a dumb question...but I don't see a tune anywhere in your mods...I see a dyno result, but no tune. You may want to have it datalogged on the dyno to see what your A/F is at.
3. Has a compression check been done? Could very well be your rings. Sounds like you may be getting some pretty nasty blowby.

Smoke is whittish-blue.

I haven't had it tuned or had the compression checked.

I'd like to do a rebuild with forged pistons and a hotter cam, but it's going to have to wait for money.

I'm more concerned with the misfire right now. I'm going to run it down to AutoZone to get the codes off the check engine light.

I'm thinking O2 sensors, mass air sensor, or timing could be a problem, but modern cars are very new to me. I've mostly worked on 60's Stangs and had help building a mild performance 5.0 with bolt-ons.

Get the car tuned or you will be rebuilding a block if its not too late already.

Please get a tune...your car will love you for it, especially with the blower and MAF. The rear O2's can be turned off, the MAF can be calibrated, and the timing set. I'm actually suprised its running as good as it is without a tune.

if your burning a quart of oil every 200 miles you got bigger problem something new o2 sensors wont fix. If its that bad either you got a really bad set of rings, or you have alot of oil leaks. the engine smoking makes me lean towards bad rings. if i was you and it ant a dialy driver i would pull the head and take a look. i bet the rings are bad.

White smoke is antifreeze. Very likely you could have popped a head gasket, and that has lead to other things. 9psi on a relatively stock internal motor with no tune and no intercooler is a crapshoot at best. Smoke on startup is an indicator that your valve seats are bad, they are letting oil seep down into the cylinder heads when the car is turned off, thats why you see it on start up. If it smokes all the time you have bigger concerns.


Adam