2004 Ford Ranger Edge SuperCab
3.0 Vulcan pushrod motor
265000km
New spark plugs and wires
Front pads
Front control arms/ ball joints
Rear drum hardware kit/brake assembly
Right rear brake cylinder
New ebrake cables
New right rear axle seal
C bearing for the differential
Crankshaft position sensor
New Coil Pack
New injectors
New Water pump and gasket kit
New Timing cover/gasket kit
New timing chains

Differential flush / gasket
Coolant flush

I've done a compression test all cylinder tested fine.

Opened the pcm everything good on the circuit board.

The spark for cylinder 4 is intermittent
Ex
Cylinder 1 0
Cylinder 2 0
Cylinder 3 0
Cylinder 4 -30
Cylinder 5 0
Cylinder 6 0

That's what the spark looks like
On idle.

I've always had a misfire in cylinder 4 only on idle
For example at a red light if I sit for too long it will misfire but only cylinder 4
It's will stumble for a couple secs with engine light flashing
Then it will stay solid and misfire is gone
A little help

 

Welcome to the forum

2004 to 2006 Rangers with 3.0l engine had a TSB for recessed exhaust valve seats.
Seen here: Ford Technical Service Bulletin (TSB) 05-26-3

Just a heads up
At idle compression is at lowest point when running, if #4 was even slightly lower compression than the average on cold test you may need to do warm engine test

Try running Seafoam or other injector cleaner in the gas tank
If injector tip is dirty fuel will drip at idle instead of spray this will cause misfire

On the coil pack cylinders 3 and 4 share the same coil in the pack, both spark plugs fire at the same time
Reverse 3 and 4 wires on the coil pack, see if problem moves to #3 misfire

Makes sure threads on #4 spark plug are clean and its wire is routed away from any metal that could cause reduced spark voltage at idle
The two Spark plugs are wired in Series, so one spark is "normal", center to tip, #3 I think, the other sparks in "Reverse", from tip to center, so threads are what gets the spark and sends it to center/wire and back to coil pack.

 

I changed the injectors and tested the wiring

 

I'm having the same problem. I have had the truck almost 3 years, and it's been a constant issue for the last 2. I found that running Seafoam through the brake booster fixes the misfire for a few days.

I am looking online now for a newer set of heads.

Also, I have to keep my left foot on the brake while stopped at a red light... and my right foot on the gas at around 1500 RPM to prevent the misfire.

I used to be able to just put it in park, and rev to around 1k RPM's and it would subside... not anymore.

 

That's the only thing I can think of but for one cylinder to be off spark it's weird

 

I replaced everything, on my 2005 Ranger STX, fuel pump, filter, coil pack, PCV, plenum gaskets, plugs, wires, injectors, MAF sensor, O2 sensors, crank position sensor, and PCM. I took it to a mechanic and they pulled the heads and number 3 exhaust valve was warped. I bought it new and I always thought that they had broke an exhaust manifold bolt off in the head at the factory but the mechanic showed me that it never had a bolt in it.
the missing bolt was on number 3.
Now it is misfing on number 4 and 5. I am going to bite the bullet and buy some rebuilt heads and get them installed in a couple of weeks.

 

Ford issued a TSB for the 2004 to 2006 Rangers with 3.0l engines
Seems there were a batch of exhaust valve seats that didn't match the heads, and they would recess and cause the loss of higher compression in that cylinder leading to misfires

Yes the fix was to install new heads

TSB here:
**************************
TSB 05-26-3

FORD: 2004-2006 Ranger

ISSUE
Some 2004-2006 Rangers 3.0L-2V "Vulcan" vehicles may exhibit:
- Malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P0300-P0306 and P0316
- Rough running at various RPM
- Rough idle
- Misfire

ACTION
This may be due to an engine exhaust valve seat recession causing a loss of compression. Refer to the following Service Procedure to diagnose exhaust valve seat recession.
SERVICE PROCEDURE
1. Perform a power balance rest to clarify if a cylinder is misfiring. Identify and keep record of any cylinder that has a concern.

2. Perform a manual compression test with the spark plugs removed to locate any cylinder that may have low compression. Refer to the appropriate Workshop Manual, Engine System, General Information, 303-00.

3. If no low compression is found per shop manual instructions, proceed with normal misfire diagnostics per the Powertrain Controls/Emissions Diagnosis (PC/ED) Manual for the appropriate model year.

4. If low compression is found and it is a cylinder that had a misfire on power balance, perform a leakdown test to determine the source of leakage that may be causing the low compression. Refer to the appropriate Workshop Manual, Engine System, General Information, 303-00.

5. If low compression is found in a cylinder that did not have a misfire detected then proceed with normal base engine diagnostics per the Workshop Manual, Engine System, General Information, 303-00.6.

If the exhaust valve is identified as the source, replace both cylinder heads with the newly released service cylinder heads. Refer to the appropriate Workshop Manual, Section 301-01A.

PART NUMBER / PART NAME
6U7Z-6049-A / Cylinder Head Assembly