Not 100% true in my experience. That will only verify that current is flowing through the spark plug wires. A timing light will still flash with fouled plugs that do not throw a spark at the tips.

 

you aren't really going to do much damage out of boost and up into a few psi of boost ranges, once you start really working the turbo to cram air into the engine is where advancing too far will cause real damage.

only if your wires are arcing to the engine block at the spark plug should you get a signal. the inductive pickup is reading the voltage passing through the plug wire. a fouled plug won't allow voltage to pass through it as the current stalls in the coil. kind of like holding back a hiccup. maybe your timing light is super sensitive, but mine is also and i haven't ever not found a fouled plug using this method. unsurprising these cars have lots of ignition issues due to the overly rich mixtures and combination of raw oil they often times have to deal with.

 

Negative. A fouled plug can allow discharge to occur along a build up path on the ceramic insulator. I've seen it in person and it's not an uncommon problem... just google carbon fouling.

Take a look at the attached PDF from NGK. Many of the conditions needed for carbon fouling are inherent to our engines.

OP - do check your plugs out of the engine and grounded... or just replace.

 

i had almost the same issue on my single turbo fd
as i program my power fc myself i solved it

so let me tell you the reason this happens and the solution
powerfc default maps have the cruising split timing set to 0. having 0 split means that both leading and trailing sparks fire at the same time. this raises the temps in the combustion chamber and also the exhaust gas temps. put on top of that that you run a 14+ afr on cruising this also raises exhaust temps (the leaner the hoter) you surely have an exhaust gas temperature issue. high EGTs. dont you have a gauge to check them? they are something very important in an engine and tunes should be made around them.

so you should get an EGT gauge. you will probably see that you temps while crusing go well over 800-900 C and thats too hot for cruising.
*also the fact that you have a cat means you have more exhaust backpressure and that raises temps even more.

SO THE SOLUTION is to either lower your AF ratio to 12-13 (i tried this first on my car and it did lower EGTs to 700-710C ) but as this lowered my MPG i tried another approach and this was to raise the split to 10 degrees on the cruising cells. this lowered the EGTs to sub 700C while i also kept my AFRs at 14.7 and kept my MPG