Bad Coil Pack on 1994 Ranger 4.0?

[JAlvarado]

Hi,

I have been chasing this issue for a few months. Truck seems to be misfiring. I tested the coil pack with ohmmeter and it is within spec. I understand that this is a "Waste" coil pack as each spark plug fires at compression and exhaust strokes. Most times, the timing gun shows some spark plug wires at 1600 rpms and some at around 800. I think this means that spark plugs may not be firing at the appropriate moment or twice as it should. See video here:

Does this mean that the coil pack is failing?

Spark plug cables are ACDelco about 4 years old with about 20K miles. Spark Plugs are about 6 months old. I have the same results with original coil pack and one from the junkyard. I hate to throw parts at it and not get it fixed if not necessary.

Thanks,

JAlvarado

 

[RonD]

Never tried a tach on coil pack spark plug wire, but what you see could be correct

Like you said it is waste spark system, so spark plugs are wired in Series, so one spark plug fires in REVERSE, tip to center, and maybe that's confusing the tach meter
If 1, 2, 3 showed 800 and 4, 5, 6 showed 1600, or visa versa, then that's what it is

the tach meter expects 1 pulse per 2 RPMs, so 400 pulses = 800rpm
But waste spark is 1 pulse per 1 RPM so meter would show double, 1,600rpm

Generally misfires at idle are dirty injector tips or narrow gaps in spark plugs, 0.054 is spec
Misfires under load(driving) are usually compression related, but can be cracked spark plug or arcing spark plug wire

I am still running my stock 1994 4.0l coil pack, new wires in 2010, after 16 years, lol
I have gotten steady misfires from cracked spark plugs, doesn't happen often but does happen
Motorcraft, autolite or in a pinch NGK will work, other brands never seem to last long

Only use regular copper or Double coating, single coating is a waste of money, because of waste spark, reverse firing on one bank