Hey All, i have an 05 ranger xlt with the 4.0, it has a missfire (0301) code, i have done plugs, wires, coilpac, and injector, compression test shows 124 psi, but still has miss, check engine light flashes at times and i know that can damage the cat so i dont want to drive it if i can help it, but im at a total loss here, money is super tight and will be for a while so any advice would be super helpful as i cannot afford to just throw parts at this thing but i need it to get to work, thanks in advance, and i hope someone knows whats going on with this thing

 

oh ya and i havnt found anything in the forums yet that has been helpful

 

Welcome to the forum

4.0l SOHC engine runs 9.7:1 compression ratio

That would put expected compression at 175psi
The 124psi would cause a misfire

I would test a couple of other cylinders with your compression gauge, just to make sure the 124 wasn't a gauge issue.
On the SOHC there is a possibility that all the compression numbers will be lower than expected because of timing chain issues, but #1 is just low enough to cause the misfire.

If other cylinders test above 160psi then I would do a Leak Down test on #1 to see which valve is leaking, i.e. listen thru the intake and exhaust while #1 has air pressure

Leak down test is when you put the cylinder at TDC and then put a KNOWN air pressure in the cylinder thru spark plug hole.
If air pressure is KNOWN to be 100psi and gauge at cylinder reads 95psi then you have 5psi leaking out which is 5% leak down, which is good to normal, over 10% is a problem
But with this air pressure in the cylinder you can go to tail pipe or intake manifold and listen for the hiss of air leaking out
Usually it is a burnt exhaust valve
But intake valves can "tulip" if overheated, causing a leak