TXMach

2003 Mach 1. K&N drop-in, Bassani catted X-pipe, Magnaflow cat-back system.

I noticed the car was hesitating and bogging under load, then about 60 miles later, the SES light came on.

I started by pulling the codes P0304 and P0316. I then read a few threads and decided to join the forum, so thanks for having me.

I checked the spark plug and it looks fine as it should, considering I replaced it about 15,000 miles ago. The coil itself also looked fine.

I swapped the coils from cylinder 4 and cylinder 1 and cleared the code. I then started the car and it seemed wayyyyyy better right off the bat. No bogging, rough idle, or hesitation as I pulled away for the test drive.

I let it get about half way to operating temp and floored it in 1st. There was a pretty big hesitation, then a loud backfire, then the car rocketed forward with no hesitation and a nice smooth rev all the way to 6,500 rpm. I shifted to 2nd and floored it again but then there was a slight bit of hesitation through the powerband so I backed off. I drove until the engine reached operating temp then floored it from 1st through 3rd. The car is honestly running wayyyyy better than it was before I switched the coils, but still not perfect. There's still some slight hesitation and a bit of power loss.

Now I'm just waiting to see if when the light comes back on it will throw a "P0301" instead of "P0304".

Does anybody have any other suggestions to troubleshoot this? What's peculiar to me is this: Why would switching two coils to opposite locations make such an improvement? If the coil is bad, I'd imagine that the problem would persist just the same. Only the cylinder of the misfire would change.

Stevo86

It's a longshot, but check the connectors for the COPs. I have seen some of them in the 4V motors get tore up over the years. It's possible you had a bad connection and then adjusted it to make it just better enough to make an improvement when swapping coils.

TXMach

Thanks for the suggestion. I'll check out the connectors. You may be right and it's possible I wiggled something around a bit and got a better connection. But still the engine isn't running perfectly. If you can think of anything else please let me know.

hpwrestler220

This same exact thing happened to me... Same symptoms and all.

I was getting no codes on my obd2 tuner so I went to my shop. They ran it for me and 2 of my cylinders were misfiring. I put on 2 other leftover COP's I had laying around and the problem went away. Was an easy fix for me. I, too, knew it wasn't my plugs bc I had changed them about 12k ago

TXMach

I really really really want to believe it's the coil. It'd be such an easy fix and I hope that's what it ends up being. Unfortunately I have no spare COPs to swap out, so I'm playing the waiting game with the SES to see if the misfire moves. So yours never threw a code?

petrock

See my reply in your other identical thread in the General Tech section:

https://mustangforums.com/forum/gene...n-cyl-4-a.html

TXMach

Thanks.

71_340

Had a misfire and a plug fouling (one cylinder) on my 02 GT, CEL never came on or any codes for that matter (not even a pending code). I replaced one COP and all is good now!

hpwrestler220

Bad COP's on these cars will NOT always throw codes...

If you can, get the car hooked up to a scanner at a shop and they will tell you which cylinders are misfiring. Switch the COP's (takes maybe 1 minute altogether) and let them run the scanner on the car again. If switching the COP's changes which cylinders are misfiring, than you know you have bad COP's...

I never threw a code. The shop just used the $10,000 snap on scanner on my car and it picked up that 2 cylinders were misfiring. I put different COPs on those plugs and VIOLA -- good as new.

TXMach

Yeah, I been reading a few related posts and have decided to just bite the bullet and purchase a new set of coils. I'm at 51,000 miles and it would probably be best to just replace them all if one has finally had it.

I went with a set of MSD blaster coils. Not sure if the plugs I use (NGK TR55s) will take full advantage of the increased spark capacity of the coils, but at least the problem will likely be fixed.

Thank you all for your thoughts and opinions, they have inspired confidence that the coil itself is the most likely culprit.

After the coils arrive and I install them I'll post again and say whether the problem has been fixed or not.