Johnphilo

My wife bought her first Mustang Saturday,which is also her dream car. It's still misfiring after I changed the wires and plugs Sunday,1-25-15 the previous owner got new calipers,pads, rotors and the Ignition Coil replaced and 3 tires not a year old yet and the fourth not 2 months old. Also a oil changed a week ago,new air filter,fuel injector cleaner,engine treatment andd Advance tested it and it showed the 3rd and 4th plugs were misfiring,which was my wife's Mustang's only problem. After everything done to it in just weeks and changing the plugs and wires less than 24 hours ago,I don't have the slightest idea why it's still misfiring. First Mustang I have worked on and would love someone's opinion who knows more about Mustangs.

houtex

It's the ignition coil, likely. But could still be plugs or wires. However, since you've done the plugs and wires, I'm going with the coil pack. Take a look at this:



You'll see there are only 3 coils in the coil pack, and they are used to fire two cylinders (not at the same time). The fact that 3 and 4 are not working indicates that coil 3 of the pack is bad.

It is also my understanding that this single coil-dual cylinder setup also fires a scavenger spark in the cylinder after firing to ensure all remainder fuel is burnt before the exhaust is pushed out. I could be mistaken, but I want to say that's what's going on.

In any event, it indicates the coil pack, while it may have been replaced by the PO, is the likely culprit, with secondary culprits being the incoming wire pin 1 of the connector, and outside chance to do with the computer or its connector.

I'd definitely pull the spark plugs on 3 and 4 and examine them to see if they're ok. Not being oiled up or something. Ensure gap is correct, right temperature range, that sort of thing. Maybe just get another two plugs as a check, or swap out with other cylinders and see if the problem moved.

Might also check compression in those cylinders. But even still, that would be *really* odd if they both had issues, being as they're on opposite sides and ends of the block. It'd make more sense if it were 2 and 3, or 4 and 5, say, being as those two pairs are on the same side and next door neighbors.

So yeah, I'm pretty sure it's ignition coil pack or the connector.

Hope that helps, and good luck!

StangMahn

I'd say its probably the coil pack. They have been known to last a long time or go out quickly. It's a pretty simple swap.

Having recently done it on my sisters v6, sounds similar to your problem.

Glenn

Pick one up cheap from the local bone yard??