1991 ford ranger 2.3 litre 4 cylinder. Engine runs rough when driving, misfires. Ran diagnostics said coil pack right side, changed right side coil pack, not the problem, no spark to one of the coils, also, when Tachometer is malfunctioning, the engine misfires and no power, sluggish.
When tachometer is functioning properly engine runs fine. Starts fine when at temp, rough when cold, tune up next, maybe cylinder not firing on back left sparkplug? EGR or PCV valve?