Hello new member here. Looking to see if anybody can help me out with my 03 ranger 3.0l truck. Bought the truck drove it for about a year before the master cylinder went out and the clutch stopped working entirely. Truck sat for about 4 months as I couldnt afford to fix it then. Got the clutch fixed along with a full tune up. New plugs, wires, and coil pack (all motorcraft). Same day I did that it went through emissions perfectly fine. Few days later I get a flashing check engine light and a rough idle at a stop. On the highway it drove perfectly fine. I did new iac, tps, and cleaned the maf just to see if I'd get lucky. Problem still there. Code its giving is a PO305 cylinder 5 misfire and a misfire code for the first 100 revolutions. It appears to be getting worse as the flashing light was only at idle but now its flashing at highway speeds as well.

So I parked it and had a mechanic diagnose it. He hooked it up to a snap on code reader thing and said injectors were reading good. Compression was showing a zero across all cylinders except cylinder 5 was showing a -20. He said it could be a valve or a bad ring issue but impossible to say without tearing into the head. After doing research o found that valve recession is a common issue with the 3.0L engine. Before I go and buy some heavy duty heads with new valves and the whole shebang maybe somebody has any experience with these that it might be something else I'm missing. I could just fix the 1 cylinder 5 but last thing I want is to fix it and then have the same problem happen to cylinder 1,2,3,4 and I'm tearing down heads again.

 

Is your fuel filter clean?
Have you done a dry and a wet compression test?

Good info here: Part 1 -How To Test The Engine Compression (1995-2008 3.0L Ford Ranger) (easyautodiagnostics.com)

 

A wise mechanic taught me decades ago to always check the simple things first.
A great video that may help you locate the misfire problem:

 

Fuel filter was replaced along with the many other things I replaced to see if I got lucky and it wasnt an engine problem. Has new plugs and wires. New coil pack. The mechanic put another pack in it to see if that was the issue but the misfire still there. I personally have not done any compression tests. The mechanic that diagnosed it only ran it through a computer and cylinder 5 showed a 20 percent less compression than all the other cylinders. Thus we are thinking the problem is engine related, specifically cylinder 5 but not sure if its valve or piston rings. Engine has 180k miles and has never towed anything. Only abuse I'd say is the rare instance of an accidental down shift to a low gear since it is a manual. I did take it to another shop for a second opinion and they think it's an electrical issue. They said that a 20 percent lower compression out of 1 cylinder is normal for an older engine. I personally think those guys just couldnt figure it out either which I dont blame them from the research I've done it's not easy to track down a misfire that is likely engine related.

 

For the sake of anyone running into this issue in the future. The problem was a leaking exhaust valve on cylinder 5. The valve seat is recessed. Common problem with the 3.0L heads apparently the seats were made with an inferior metal and they tend to resess over time causing the valve to leak. Replacing both heads with reman heads from adv cylinder heads.com. They assured me that they address this problem by re inforcing thos valve seats. Have not installed yet but I will post back on results.