Misfire in cylinder 4. I changed the spark plug and wire but it still misfires a bit at idle. Enough to shake the cab a decent bit. The check engine comes off and on. Wondering if this is enough of a difference in compression to cause the misfire? Or do you guys think it’s more likely the fuel injector or distributor cap?

 

Need lots more info.

What engine?
What year Ranger?
How many miles?
Are you the original owner with first hand knowledge of the vehicle's maintenance?

List all cylinders when reporting compression pressures. Knowing the compression of adjacent cylinders is often helpful.

Have you a code reader? Pull codes when the CEL is on, them report them here.

A distributor cap problem is not possible as your engine has a coil pack.

One easy thing to do is dose the tank with Chevron Techron fuel injector concentrate before a stint of local driving. You may get lucky.

Making this a poll question seems odd.

 

3.0 vulcan, 2002 ranger with 219k miles. I bought the truck a couple weeks ago. It’s a P0304 code. I included a picture of the compression of cylinder 4 (~130 psi) and the adjacent cylinder (~155psi). All the spark plugs have wires that come together at the coil pack I assumed that would be the distributor. It had me fill out information about the truck when I made my account, I thought that would be publicly visible, my mistake. Hope this helps. Thanks for the response!

 

Double the dose of Techron. Put the 12 oz. bottle in 6 gallons of gas etc.
At 219k miles, lots could be wrong. Beginnings of a burnt valve? Adapt air into the cylinder when both valves are closed and listen at the throttle body and tail pipe.
A valve spring could be bad.
An injector could be faulty or just clogged.
And yes, one side of each paired coil (waste spark system) can go bad.
Any smell of exhaust in the coolant reservoir?

Good luck