2.3L ('83-'97) Cylinder four mis-fire when cold

[ksimp]

1996 Ranger extended cab XLT
2.3L 260,000 miles
5 speed
400 miles on rebuilt engine

Engine skips while cold.
CEL starts to blink at around 124* and throws a code for mis-fire on cylinder four (always cylinder # 4).
When engine warms up, skip is gone and no more mis-fires are registered.

It is almost like there is something turned on when the engine is cold that is causing a vacuum leak and closes when the engine is warm?

Any suggestions are greatly appreciated.

Thank you

 

[Uncle Gump]

When cold... a richer mixture is required.

I would ask if you reused the old injectors... replaced them... cleaned them...?

I think i would try checking for a vacuum leak around number 4 when cold. I use propane...

 

[ksimp]

Hi @Uncle Gump. Thanks for your reply.
I replaced the #4 injector with a new Motorcraft unit from Rock Auto. It matches the old one (and the other three old injectors).
I'll try spraying around #4 with Carb cleaner when cold to see what happens. I've also thought of disconnecting and capping off the vacuum lines (except the fuel regulator) when cold for testing.

 

[SenorNoob]

Unless you seriously cleaned the old injectors, I'd bet they are flowing differently than the new one. The computer has no good way to measure that and adjust for it since it only has one O2 for all four cylinders.

 

[ksimp]

More info...
Before I rebuilt the engine, I'd installed four ebay cheepo fuel injectors. Thinking those may have been part/all of the misfire problem, I took the original Motorcraft injectors and worked on those. I ran pressurized cleaner through them while verifying the spray pattern. After installing those, I checked for the clicking while the motor was running. I also verified the wiring/PCM using a noid light on each injector circuit.
I've uploaded a new video to Rumble minus the sunlight glare at:
1996 Ford Ranger 2.3L Cylinder Number 4 misfire

 

[ksimp]

I've replaced the valve springs. The engine runs much better. Still a little mis-fire on #4 until it warms up to about 130*. No more CEL.