I have a 06 4.0 ford ranger that has a misfire on cylinder 5. I have replaced the spark plug, spark plug wire, ignition coil and fuel injector (looked very dirty to me). I've also checked the compression on the cylinder and it is at about 150psi. Does anyone have any recommendations on what to try next?

 

Assuming #5 misfire was present before doing any of the above work?
Possibly an IntakeManifold gasket leak at Cylinder5?
Can try swapping #5 Plug or Wire with another good Cylinder, see if problem moves to that other cylinder?
What Make+Model Plugs+Wires+CoilPack did you use?
Plug gaps were proper before install?

 

Yes the misfire was present before any work was done. Problem does not move to different cylinder when i swap plugs and wires. I used a oem coilpack and I'll have to check what kind of spark plugs and wires in the morning. The plugs are set to a .040 gap.

 

Compression test needs to be done on all 6 cylinders with all 6 spark plugs removed, at "one sitting", cold engine

150psi doesn't mean anything on its own because there is no reference point

If the other 5 tested as 180psi then 150psi is bad
This has to do with the gauge and the testing conditions at that "one sitting"
You could test just 4, 5 and 6 but I would test all 6

The 4.0l SOHC engine runs 9.7:1 compression ratio(CR) so 175psi would be expected
Generally speaking/rule of thumb, expected PSI is CR x 18
9.7 x 18 = 174.6psi

15 is sea level air pressure, + 3 for mechanical compression in the cylinder, that's were the 18 comes from


A "misfire" doesn't always mean the cylinder didn't "fire" at all, the computer reads crank/cam rotation down to the milliseconds, when a cylinder "fully" fires it will add to that rotation
If a cylinder "partially" fires it won't add as much "power" to the rotation, and that can be seen by the computer because of the change in rotational speed, usually based on cam sensor because if has more "resolution" spinning at 1/2 the crankshafts RPM
If compression in a cylinder is not within 10% of the other cylinders then it won't add the same power to crank/cam rotation, so it can have enough compression to "fire" but not add the same power

 

Plug gaps should be 0i054=0m0014; this may be at least part of the issue.
Plugs should be FordMotorCraft# agsf22fm\sp500or OriginalEquipmentMaker AutoLite# app103.
Non-OEM plugs are notorious for causing misfires in this engine.
Ditto on Compression check; RonD's advise is always good.
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