99 Ranger P0304 And Running Rough! Help!

[hinton08]

1999 Ford Ranger 4WD 4.0L Automatic Trans. A few months ago, I swapped engines in it. It would always miss when you first start it and under a light load. I did a combustion check and found out there was a combustion leak. Owner insisted on swapping engines due to combustion leak. Before I swapped engines, it would constantly have a P0304 Cylinder 4 Misfire. We figured that was because of the antifreeze leaking into the cylinder. So, we swapped engines, and it run ok for a little while, and now its doing the same problem as it was. Every now and then, it will come up with a P0304 Cylinder 4 Misfire. It has new plugs I put in when I swapped engines, I swapped the ignition coil and wires over from the old engine because the owner bought them recently. We used the engine wiring harness off the engine we put in due to old harness having several frayed wires. New mass airflow sensor, coolant temperature sensor. Everything else, we left on the engine we put in. We are stumped as to what could be causing the cylinder 4 misfire? Another mechanic told the guy it needed an ECM so he took it to the Ford garage and had a new ECM put in and programmed...still does the same thing! The owner is okay with the engine swap because he insisted on it and there is not a combustion leak now but is kinda irritated he had to put a new ECM in it and pay $180 to have it programmed. Only conclusion i can come up with is the oxygen sensors are bad? But there is no code. I hooked my scan tool up to the truck, all O2 sensors fluctuate from around 0.1V to 0.9V like they should, although it seems like they are a little sluggish, but not enough I would think to cause the trouble it has? Any suggestions to point me in the right direction would be highly appreciated! Thanks and hope to hear from somebody soon!

[Davescort97]

This link will tell you all you need to know for P0304.

http://repairpal.com/OBD-Code-P0304

[mazda master]

Originally Posted by hinton08

1999 Ford Ranger 4WD 4.0L Automatic Trans. A few months ago, I swapped engines in it. It would always miss when you first start it and under a light load. I did a combustion check and found out there was a combustion leak. Owner insisted on swapping engines due to combustion leak. Before I swapped engines, it would constantly have a P0304 Cylinder 4 Misfire. We figured that was because of the antifreeze leaking into the cylinder. So, we swapped engines, and it run ok for a little while, and now its doing the same problem as it was. Every now and then, it will come up with a P0304 Cylinder 4 Misfire. It has new plugs I put in when I swapped engines, I swapped the ignition coil and wires over from the old engine because the owner bought them recently. We used the engine wiring harness off the engine we put in due to old harness having several frayed wires. New mass airflow sensor, coolant temperature sensor. Everything else, we left on the engine we put in. We are stumped as to what could be causing the cylinder 4 misfire? Another mechanic told the guy it needed an ECM so he took it to the Ford garage and had a new ECM put in and programmed...still does the same thing! The owner is okay with the engine swap because he insisted on it and there is not a combustion leak now but is kinda irritated he had to put a new ECM in it and pay $180 to have it programmed. Only conclusion i can come up with is the oxygen sensors are bad? But there is no code. I hooked my scan tool up to the truck, all O2 sensors fluctuate from around 0.1V to 0.9V like they should, although it seems like they are a little sluggish, but not enough I would think to cause the trouble it has? Any suggestions to point me in the right direction would be highly appreciated! Thanks and hope to hear from somebody soon!

o2 sensors would not cause a misfire on only 1 cylinder.So lets start with basics first. i assume your compression is the same on #4 as the rest of cylinders.next i would for sake of a few minutes change around 2 plugs to seeif misfire moves(seen quite a few ford platium plugs bad out of the box.
next change around 2 injectors(only fuel rail has to be let go,no intake has to come off to do this.)also can you watch this misfire on a scanner or can you just read codes?if you can watch the misfire occur (like on fords power balance test)does it occur at idle only or while driving underload or both.I have also seen intake gaskets leak on these but if you never had intake off with engine swap i don't think it would be the same cylinder.
just try some of tis and report back.good luck

[cam 540]

I'm having the very same problem with my 99 Ranger 4.0 so is a friend of mine with his 97 Ranger 4.0 we have the same #4 cylinder misfire code P0304. Both trucks are burning up a plug every 3,000 miles the plug turns brown and the trucks start missing really bad Both truck have had upper and lower intake gaskets changed full tuneups we just cant figure out whats causing this to happen even a Ford Mechanic friend of ours cant figure it out either it getting really annoying and wandering if you have solved your problem yet???? any help please!!!!

[KnobbyTires]

Is anyone losing antifreeze slowly...say a quart every month or two. That was to be my warning of a bad head gasket and eventually a warped head... then another one cracked... huge loss of compression noticable. I hope it's an easier fix.