Re: Ignition warning, is it true or false?
The problem with the timing light trick -
If the wire is partially broken the light will still flash.
If the plug's fouled or shorted, the light still flashes too.
All it's telling is there's high voltage in the wire, but not how much or how it's firing in the chamber.
Same way with the MM neon light testers.
The phoney plug testers in the pictures - the ones made specifically for HEI have a longer gap - since the HEI can fire a bigger gap. They look the same, but the center electrode is back inside further, giving that longer gap.
A separate plug will work too. Just ground the shell and look at the spark - set the gap to about normal.
Should be a bright blue thin spark with a definate "snap" to it.
Not bright, intermittant, or a red spark indicates troubles.
But - like was mentioned - a good scope will tell you much more at a glance. Even then, sometimes all the ignition voltages are correct - because the ingition system is fine.
But a dead cylinder, or partly dead, still can be detected by pulling wires. That's why any decent automotive scope has the ability to kill cylinders one at a time and in groups. They are safer, they don't allow that cylinder to fire by shorting the primary, there's no high voltage generated that can destroy something like pulling wires could. But ya gotta do what ya gotta do.
Remember Factory service manuals are constantly calling out special "factory" tools and reasons you need to take it to the dealer - and pay him. Most factories have their own "authorized" scope. I know, I spent most of my life involved with supplying those dealers with their test equipment - and training them.
A dead or partially dead cylinder (misfire) can be caused by many things other than ignition - most common is lean mix, usually due to a vacuum leak, low compression, flat cam, EGR leak, weak spring, valve action, injector, etc. - lots of things.