I have a 1999 Mustang GT 4.6L with 45,500 original miles. It is running rough as if it has a misfire and running off only 7 cylinders but I have no check engine light on. While running I removed each coil wire plug 1 at a time to see if there was a spark issue. When disconnecting 1 at a time at the engine begins to stumble even more until I get to cylinder #3 (2nd from from on passenger side). When I unplug that coil there is no change on the idle so replaced that ignition coil and it still does the same thing. I used my volt meter and it registers at almost 15volts which is normal. I even removed the coil and using a spare plug to make sure it is sparking and TRUST me it gets spark. LOL! I have checked the TPS, MAF, and IAC which working properly but again no check engine light on and I am stumped. Can anyone provide me with ideas as to what else to check?

 

Clogged/malfunctioning injector? If you are getting spark to that cylinder, I would think no fuel would be the next most likely culprit.

 

It could have a vacuum leak on the intake at that cylinder. Could also just be a fouled plug in that cylinder.

Also check for oil or anything down in the hole.

 

Have you done a compression test on the cylinders? If that finds something wrong with a cylinder or cylinders, a leak down would be the next step to figure out the exact problem.

Could be a valve isn't seating properly or you've got excess blowby on the rings? Those types of misfires don't always throw a CEL.

Any smoke out the rear?

 

OK update.......... Now have codes p0300 and p0302. The I checked #2 cyl and seems to NOT be getting voltage and I checked the other cylinders and the voltage is speratic ranging from 0.6v - 1.8v. How is this possible and the car run and be driven? The volts should be 10 -12 if I am correct. Also what would cause the low voltage? It has a new PCM that was installed a couple of months ago. I am working on printing out wire diagrams so I can check the grounds but this is strange and I am at a stand still. HELP!! LOL!!