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Misfire on an 04 Mustang 3.9
02-21-2014, 10:18 AM
Post: #1
Misfire on an 04 Mustang 3.9
I have been trouble shooting a misfire condition in my 04 Mustang. I did a basic tuneup with plugs and wires and this did not cure the misfire. I tested the coil and according to the book it is good. What I discovered was the the #1 and #3 terminals at the coil have a weak of no spark condition. This confuses me because all test done on coil were correct and in the parameters suggested by the book. As you know that the coil is set up so that one coil fires two plugs as 1 and 5, 2 and 6, 3 and 4. Could one side of the coil function properly and the other side be bad? As with the #1 misfires but the #5 does fine and #3 misfires and #4 does fine. Thanks ahead of time.
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02-21-2014, 11:27 AM
Post: #2
RE: Misfire on an 04 Mustang 3.9
Yes, that is possible. To confirm, try swapping the good coil into another position and see what happens.
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02-21-2014, 02:54 PM
Post: #3
RE: Misfire on an 04 Mustang 3.9
(02-21-2014 11:27 AM)Rupe Wrote:  Yes, that is possible. To confirm, try swapping the good coil into another position and see what happens.

Thanks Rupe:
Replacing the coil pack did the trick. Thanks so much for your input. I am forever grateful.
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03-01-2014, 04:37 PM
Post: #4
RE: Misfire on an 04 Mustang 3.9
Here I go again. I am working on my son's 99 Ford Explorer, 4.0, 5 speed std.. It was missing on 3, 2, and 1 inter-mitten so I replaced the coil (it was bad) and the wires along with the plugs. I continue to have a inter mitten miss on #3 cyl.. Any ideas?
Thanks ahead of time
Rick
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03-01-2014, 05:55 PM
Post: #5
RE: Misfire on an 04 Mustang 3.9
Working on stuff like this with limited resources is always a bit of a chore, especially on an older vehicle. What I would do is swap the new coil to another location and see if the issue continues on the same cyl or follows the coil pack to the new home. It's one of those things where it's going to be hard to pin point a sticky injector versus a bad connection or another bum spark plug without a little hunting around. If you have access to a full function scanner you might be able to get a reading on fuel trim or O2 sensor output to nail it down.

Speaking of which, have you gone through all of the vac hoses on this 15 year old car? You may stumble on something there causing a slight skew in the fuel mixture. A vac leak near the manifold can lean things out and a vac leak near a MAP sensor can richen things up. See where this is going?

BTW, when you had the plugs out did you compare them to see if they are burning ok and the same color on all cyls?
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03-05-2014, 11:48 AM
Post: #6
RE: Misfire on an 04 Mustang 3.9
Thanks for your input. I will look for the vac leak to see where that takes me.
(03-01-2014 05:55 PM)Rupe Wrote:  Working on stuff like this with limited resources is always a bit of a chore, especially on an older vehicle. What I would do is swap the new coil to another location and see if the issue continues on the same cyl or follows the coil pack to the new home. It's one of those things where it's going to be hard to pin point a sticky injector versus a bad connection or another bum spark plug without a little hunting around. If you have access to a full function scanner you might be able to get a reading on fuel trim or O2 sensor output to nail it down.

Speaking of which, have you gone through all of the vac hoses on this 15 year old car? You may stumble on something there causing a slight skew in the fuel mixture. A vac leak near the manifold can lean things out and a vac leak near a MAP sensor can richen things up. See where this is going?

BTW, when you had the plugs out did you compare them to see if they are burning ok and the same color on all cyls?
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