Hello! Long time reader of the boards, first time poster. I have a 2002 Mustang GT with only mod being K&N air filter. The backstory on the problem is that I parked it in November of last year and didn't drive it again until March. I STUPIDLY chanced it and drove it on the old gas. It misfires. Badly. I cannot siphon out the gas so I add octane booster and fill it the rest of the way (about a half a tank) with high octane gas. I drive it on that for a bit and it continues to misfire and throws the code for valve 6 misfire. It's due for a spark plug change anyway, so I get Motorcraft nickel plugs and change all 8. The old ones were gunked up, so I did use deep creep to loosen them (I have never had to use this in there before). I did the cautionary air compressor blow out before I removed the old ones. I also know that I rewired the boots correctly. I also used the torque wrench set at 13.5 ft lbs. After the spark plug change, it is now not starting. I expected some nasty smoke and time to burn off any of the deep creep that made its way down there, but I have cranked at 6 times with only 2 times producing a turnover which only lasted a few seconds. It has not thrown a code, but but shows monitors on misfire, fuel system and 'comprehensive components'. Should it have burned off by now? Am I looking at something else going on? All feedback welcome and thanks in advance.

 

PS. When I start it and give it gas is when it stays on a few seconds. I'm not giving it aggressive gas, but it revs up high very fast and then dies.

 

You might have a clogged fuel filter, sediment from the tank may have gotten into the gas line.
This is easy to test, see if it will start and run when you spay starting fluid into the intake.
I wouldn't run it more than 5-6 seconds like this, starting fluid tends to wash oil off the cylinder walls.

 

PPS. I gaped the plugs to spec (0.054). I have not changed the fuel filter in 3 years (and am getting a sick feeling that I need to now.) I did not have to touch the fuel rail to change the spark plugs, it was easy to work around it. I did double check that everything up there is securely in place. I do not know if the ignition coils have ever been replaced, but they did not look too gunked up inside and no burns. The battery is new. I don't see any electric arcs while it is starting. (Just trying to field out some of the obvious problems)

 

Thanks, Chromeshadow. I didn't think to test it like that.

 

something else you might want to check is vacum lines and if you have a cai ,check the seal between the maf, i had a problem back a couple months ago when i replaced my tb, kinda like what you described (revs up high very fast and then dies.) , i redid the connection between maf and cai and wala idle was back to norm

 

check the IACV idle air control valve. its on the throttle body with the large vacuum line connected to it... if the vacuum is clogged it will always die... mine was partially clogged when i bought the car...so didnt really die but when WOT it lost all HP... check all vacuum lines... make sure there in the right place also... one in the wrong place and it will DIE or stay redlined.... also make sure they dont callapse when running, old vacuum lines callapse under presure.

let us know...