I have an 01 Ranger that has a misfire in cylinder 4 (according to the CEL). I’ve replaced plugs, wires, coil pack and fuel injector. Seems after I installed the injector the rough idle and miss got worse. What should be my next thing to check?
Thanks!

 

Welcome to the forum

First thing you should check when you have a misfire, even with no code, is compression, this is a mechanical function so is good or bad, no grey area, and it saves time and Money
Cold engine
Remove all spark plugs first, keep them in order 1 to 6, so you can inspect the tips
Test 1 cylinder at a time and write down results
Press gas pedal down to the floor while cranking engine over for the test, need to hear at least 5 "hits" of compression stroke, you will know

There is no "correct number", that is not what this test is for, numbers vary by pressure gauge used, starter motor and battery condition(cranking speed)

Test is to compare all 6 numbers, to see if 1 or more cylinders are lower than the others
If 5 cylinders are 155-165 and 1 cylinder is 140 then that would be an issue, usually burnt exhaust valve, the most common reason for a misfire on all gasoline engines
You can do a WET test after to confirm its a Valve leaking not Rings

Changing spark plugs, wires and coil is fine, these ALL wear out over time
But compression test should have been next


A Gasoline engine needs 3 things to "fire"
1. spark, at the right time
2. fuel mixed with air
3. compression, liquid fuel can NOT be ignited by a spark, only fuel VAPOR will ignite with a spark, compression HEATS up(compresses) the fuel to vaporize it

Out of the 3 things only one has no way to be intermittent because it mechanical, it is either good or bad and doesn't change "states" randomly, compression

Spark and fuel can both be intermittent, so can be a pain to diagnose, so best to rule out compression issue FIRST, just to get that off the table or find out it IS the issue

 

Thanks for the input! Turns out cylinder 4 is only holding 90psi. The other 5 are holding 150psi. Guess I’ll be making a trip to my local mechanic

 

Bummer
Swapping or repairing the heads is just wrench work, no special knowledge or tools are needed, well a torque wrench but just for the head bolts

 

I’ve done some research on the 3.0 and apparently it’s very common for the Exhaust Valves to recess downward over time and cause a rough idle without any codes popping up, ultimately causing lower compression sometimes. That might be the issue.

 

That was 2004 to 2006 3.0ls that have that issue, its was not "common" but there were enough Ranger 3.0ls for Ford to issue a TSB about it

TSB seen here: https://www.therangerstation.com/for...n-tsb-05-26-3/

I would expect 2003 and 2007 might have some spill over but 2001 would be a long shot for this issue

But exhaust valves are the most common issues for misfires not related to spark plugs on ANY gasoline engines
They just run very very hot, so any slight defect or glitch will cause them to leak