Inline spark testers - any good?

As I was diagnosing my broke-ass parts runner pickup on the side of the road today (breaking down around the corner from your shop and a block-and-a-half from AutoZone is "good luck" of a sort, kind of like when you don't get that much dog E36 M3 on your shoe) I began wondering about spark testers. Without having the means to clean up any potential grounding points on the side of the road, short of scraping the metal with a knife/screwdriver/spark plug electrode, it's hard to positively rule out a bad ground on the plug when you're trying to test a no-spark condition.

So, in the future, could I grab a cheapo spark tester from my local big box parts store and trust it to perform in a consistent manner as a diagnostic tool?

The neon tube ones suck balls, they'll light up even if the spark is too weak to jump the gap on the plug.

The best kind are the ones that look like a sparkplug with an alligator clip on the side.

Shawn

Or you could toss an extra plug in the truck and just use it with your jumper cables.

I just use a known good plug from a previous tuneup.

Trans_Maro said they don't work right but I used my "KD" brand version for decades with total success. I finally dropped it and broke the glass shield. So I bought a HF version. I haven't used it much so I don't have an accurate report to give. I do recall using it to successfully diagnose a riding mower.

To be clear, I'm talking about the kind that you unplug the wire and put it inline with the plug. I have my doubts about the type that you just touch to the outside of the wire.

They do light up, but if you've got a bad condenser or a wire with high resistance, they'll still light up. It doesn't take much to make a neon tube flash.

I'm just saying jumping an actual gap is a fer better way of checking for spark.

Shawn