1998 Ranger 4.0 misses for several min. when cold..

[raggedyann]

I replaced the upper intake gaskets. seemed to help some but it has a dead miss when first started. The colder out the worse it misses. shakes the truck.
About 3 minutes or so, it will smooth out and miss disappears ???

 

[RonD]

Old/failing Spark plugs can act that way.

Also leaking valve guide seals will cause cylinder to be oil fouled on first start up.

Cold engine, disconnect coil pack connector, you want a no start
Crank engine for a few seconds
Pull out all spark plugs and inspect for oil fouling.

While spark plugs are all out, if possible, do a compression test on all cylinders.
Low compression will cause your symptom as well.
4.0l should generate about 155psi - 165psi with good battery and no spark plugs in, on each cylinder, sea level to 2,000ft

If it was a coil pack issue I would expect a Check Engine light(CEL) which you don't mention, but the misfires should also generate a CEL as well so you may be looking at a computer problem, but they don't "fix" themselves after warm up.


Long shot is the start of a head gasket/cracked head issue, but you would notice more white in exhaust on start up and a small loss of coolant without signs of a leak, which you don't mention.

 

[raggedyann]

2 spark plugs were weak, well my buddy picked up a set and installed them . miss is gone now but the wrong plugs were installed.
autolite 764 were installed
ap-103 is what it calls for in the autolites
will the 764 harm it until I can install the correct ones ?

 

[RonD]

No, 764 is a colder plug but has the same dimensions, so won't harm the engine at all.
103 is a warmer plug.

Colder or warmer is the spark plugs heat range, 764 is a D15, 103 a D16, larger number = warmer range

What that means is that the 764 may be easier to foul with oil or rich fuel mix, a colder plug bleeds off heat through its threads faster than a warmer plug.

Too warm a plug can pre-ignite fuel(pinging) or melt at the tip


You can use the 764's until they wear out, they should wear out before a set of 103's but still will last quite a while

 

[Big Jim M]

Another way of saying colder and warmer is to say the more rpm the engine is turning the colder the plug you would want in there. As the more rpm the more HEAT the plug will receive. Then again an engine that never goes to high rpm will require a much warmer plug that normal.
As always the factory of all engines has done these tests for us. The FACTORY plug is always the one to choose. Disregard all plug advertising.
Big Jim

 

[enjr44]

You can use the 764's until they wear out, they should wear out before a set of 103's but still will last quite a while

And that "quite a while" is like 50,000 miles!!!