Hi!


So I have a 2006 GT automatic. I did the following upgrades on the car: K&N air intake, Graniatelli 62mm throttle body and SCT Tuner with tunes from AM and run full synthetic Mobile 1 oil, and Scott Drake fuel rails.

I am going through the following issue: leave the car overnight, start it up in the morning... engine runs ok... start driving the car and after a couple of minutes if starts giving cylinder misfire on #8 (the engine starts being a bit 'shaky' also). Run the car for a couple of minutes and as the temp needle starts getting close to the mid point, the misfire stops being as noticeable and then at some point it completely goes away and engine runs really smooth again.

I did the following to try and fix the issue: replaced all spark plugs (had Champion and put in Motorcraft), replaced the COP, swapped the spark plugs between #7 and #8. Had a broken locking clip on the spark plug cable on #8 so I replaced the plug. Tightened most of the screws around the #8 cylinder - intake manifold and the valve cover.

Any ideas on what the issue could be? Has anybody else ever experienced it? If i let the car run for about 5-10 minutes before I drive off in the morning the misfires don't happen... I am reaching my wits' end on this issue. Only thing left I haven't tried is returning the car to stock on the tune (and I will try that tonight)...

 

Well, if you replaced the spark plugs perhaps the next place to look is the coils? Maybe switch coils with cylinder 7 and 8 like you did with the plugs and see if the misfire switches too...

 

Already replaced the #8 COP with a brand new one in the process of troubleshooting this...

 

Oh, my mistake I missed that in your original post. Have you tried retuning the car to stock to see if it's tune related somehow?

 

I'm going to try that tonight... but other than that I am completely out of ideas...
Someone from Napa Parts told me something about the gaskets between the intake manifold and the engine and those causing issues but it doesn't quite make sense as the car works well if I let it idle... only once I start driving it from a really cold start it starts acting up and it doesn't last too long...

 

Did you try talking to AM?....

 

That's sounds like an issue I had with my Subaru last year. Could be a tiny bit moisture that got in somehow, and causing it to misfire until it heats up burns it all away. Maybe the gaskets are bad and with the extreme cold it allows the tiniest bit of moisture in?

 

Put the stock TB and air box on and put it to stock tune. See how it runs.

 

Ok. I'll try the stock tune tonight...
Then I will try Osiris's suggestion tomorrow night if it still fails.