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.

 

wow lets start with the coil packs they are known to go bad.
do you have a gas smell in the oil? +over rich condition washing the cylinders.
smoke on startup-blue, black or white. blue=oil, black=gas, white=water/antifreeze usually a sweet smell.
any over revs/missed shifts to break a valve spring?
o2 sensors would be bad with all that oil or antifreeze soaking them.
I am not sure about the PVC system with the supercharger but it could be an issue.

 

Pull a plug and see what it looks like and or take a pic of it. Also, with a supercharged app, you are going to need to run a tighter gap than the stock .054. if you are running stock gap, chances are you have fouled more than one plug out. I'd suggest pulling them all and replacing with something like Motorcraft AWSF-22C (one heat range cooler and copper) gapped around .035-.040 and see if that makes a difference.

I am really interested in seeing how your plugs as of right now look.

 

I have 2 major problems right now:

1) Misfire - This is my daily driver and this should be fixed ASAP.

2) Oil burning

I posted both problems in case they were related. I recently bought this car so I'm still getting to know it.

for the Misfire...

I recently changed the spark pulgs (just a few weeks ago). I checked the new plugs and they look fine. I took a photo of the old plug that was in #7. Both times I've hooked the computer up to my car it has said that #7 is misfiring. The other spark plugs looked normal for 65K miles. Here is the plug from #7:


Again, this was replaced a few weeks ago. It was the first thing I tried. The problem wasn't fixed immediately, but I found an air leak in the S/C plumbing, then the problem was solved. But why has it come back?

I'm going to replace the wires tomorrow. I wasn't able to get any new cables tonight because the stores don't carry one with the right boot. I'm going to try a dealership.

If the new wires don't fix the misfire, I'm at a loss.

I thought the problems might be related, and maybe it is if burning oil has ruined the O2 sensors. This car has been raced quite a bit, so I was planning on a re-build soon anyway to replace any seals/rings/etc that have suffered because of the mods and racing. While the engine is apart, I'd like to add forged pistons and a hotter cam. This hasn't been done yet because of a lack of money.

I have not had a mis-shift or over-rev, but I'm the 3rd owner. I haven't had the opportunity to really play with it yet.

I haven't taken the car to the track yet, and I've been babying it until these problems are fixed.

I will let you know if the problem is fixed after the wires.

Thank you so much for the help!

 

You got something going on with #7... do a compression check ASAP and see what it comes up with.

 

i have heard horro stories about supercharged stock bottom end 96-98 mustangs that are un tuned.

 

Turns out it was tuned. The previous owner just didn't know it. I talked to the performance shop where everything was done to get the history.

It turns out the misfire was pretty serious. The #7 piston is broken and has caused damage. It looks like I'm in the market for a new long block.

The guys at my performance shop said that if a piston goes out, it's usually the #7 for whatever particular reason on the 4.6L.

This problem has been overlooked for years. The previous owner first had a problem with it in 2000. The non-performance shops he too it to (one was the dealer) replaced other things, made the "check engine" code go a way for a while, but never found the problem.

I thought I'd post the results of this problem in case someone else runs into this problem.

Also, since I'm putting a new engine in, I'm trying to decide what performance mods, if any, I want to (can afford) to put in while it's out of the car.

Are forged pistons really worth it?

Any major successes with cams? Prorpably looking at com cams.

I may leave the motor with the stock set-up and put the BBK T.b. and super back on.