06 GT random misfire

[Tom Manner]

2006 GT 5speed. I'm having a problem that figure put at all. Short version of the symptoms. Random cylinders misfire at idle and low to mid-ish rpm's under load, and it lopes. Burnt matches/sulphur smell from exhaust. I have checked all the plugs and coils. Checked the MAF. Changed the TPS. Changed the fuel filter. Checked all 8 injectors and they are functioning. Run injector cleaner through it (do that regularly anyways). The battery and alternator are both ok, I changed both and no difference. Air filter (KNN cold air) is fine as is the throttle body and TB motor. I feel like I'm missing something else ive checked but idk long day. Have a pressure tester so I'll check for a blockage in the exhaust tomorrow. Don't know how to check the Evap system. I only have two ideas at this point what it could be and I don't even want to think about it(2 catalytic converters $$$$). Anyone else have ideas/suggestions/help? Thanks a lot guys.

 

[SpartaPerformance]

Are you getting any codes?

 

[Tom Manner]

Something like "misfire on random cylinders". More or less no particular cylinder seems to misfire more than any other is the gist of the code. Thanks for the reply too. Any other ideas?

 

[SpartaPerformance]

So you're getting a p0300. You need to find somebody with a scan tool that can do a power balance test, injector flow test, relative compression test. One of those should reveal the issue.

 

[Tom Manner]

I really appreciate everyone's help. I feel like a dumbass right now. At least 3 plugs went bad AT ONCE. 100k mile plugs my left nut. They looked perfect, but they weren't. 8 new plugs and she runs perfect. In short, please remember Occam's Razor. And again thanks for all the help from everyone.

 

[bigb427]

Ford came out with a bulletin awhile back that states if the vehicle is used in "severe duty" to change the spark plugs on 3-valve motors at 60K miles. I recommend to everyone to change them at 60K miles regardless of usage. The plug gap shows quite a bit of wear at 60K miles on most vehicles and this wide gap puts more stress on the coils, which in turn can cause them to fail. The higher the mileage on the O.E. plugs, the higher the risk of coil failure. I have seen this a lot on 5.4 3-valve engines in f-150's and Expeditions, and to a lesser degree on Mustangs and Explorers with the 4.6 3-valve engine.

 

[Tom Manner]

That's exactly what I think was wrong with these. Since you can't adjust the gap(wonderful idea Ford) the gap obviously widens as the electrode wears. My case certainly isn't heavy duty either.