Why Are Some Vehicles Super-Picky About Spark Plugs?

Just saw a Scion thread mentioning issues and a few folks mentioned the need to run NGKs, and I've certainly heard a number of instances of folks saying "yeah, that model will just basically freak out with the wrong brand of the right plug."

So what properties to spark plugs have that can make this so?

1. Heat range? Doesn't seem likely; if there was an "offset" with a brand being hotter/colder you could adjust the model, and it doesn't sound like it's a fouling issue, necessarily.
2. Resistor plugs? They have them or don't? Variation in resistance? Is it even a thing anymore? I was just reading a Kevin Cameron book on sportbike tuning which clarified that the resistors were basically there to kill the low-voltage trail that generated electrical noise after the brief powerful spark that emptied all the high-voltage charge, and that coil-on-plug having done away with the plug wire "antennae" it doesn't matter much anymore in most modern applications.
3. What about the core? Sometimes it sounds like a car will be happy with NGKs, and it doesn't care whether they're basic or platinum plugs, but won't work right with either variety from another brand? Once you've got a core of X material from electrode to connector, what differs?

What else varies from plug to plug? What's the actual crux? I mean, spark plugs don't have printer-cartridge style ID chips (yet), so it's not like the car can tell anything about the plug apart from its physical properties... If it's a quality thing, what are the flaws?

I note that the ones that came out of the FRS are the multi-ground kind. Says Toyota on the package

I could see quality in build being a factor, which could vary from manufacturer, beyond that I've never understood it either

Like running Champion plugs in a AC VW.

Something in the metal made them tend to seize

They ran fine.

I've bought a LOT of Mercedes that "don't run right, can't figure it out" that had multi prong plugs and when I put regular Bosch plugs in all was well. 

95% of all Chrysler products run "best" on the same E36 M3ty Champion plugs they've put in them for years, unless they have ngk's in them.

My avalanche hates the plugs I have in it currently, especially when cold, because they are way colder than stock. But I also have a way advanced timing from stock tune I'm running.

This has been an issue since the 60s when I started working on cars as a professional. I worked on imports during the 60s and 70s. NGK was the go to plug for Japanese cars and Bosch was what worked in German cars. British, French and Italian cars did not seem to be as picky. This was happening before unleaded gas as well when we changed plugs at 12.000 miles after cleaning them at 6,000 miles.

I put NGK copper or platinum in basically everything and have never had any issues. 

Agreed, NGK seems to be the answer for most things.  The NGK iridium is basically my go to these days.  

On T5 and T7 SAABs, from my understanding, you need to use NGK plugs because somehow the ECU used those for knock sensing.  Anecdotally, I have always used NGKs, clean and regap them every oil change and have never had one of the infamous DIC failures that seem to plague SAABs.

Gm v6's with the distributorless ignition hate bosch plugs.  

I have a theory.  You might have the same heat range, size, application, and flavor of each brand and they all test the same for everything on the planet when you use a multimeter with a 9v battery.

But then you throw 50,000 volts through it for a few million cycles, get it hot from running the engine a few hundred times, and maybe the alloy of copper/platinum/unobtanium that Champion uses is a little different than the one Bosch uses.... enough that the qualities of the high voltage from a Toyota ignition system acts differently than the one in a Chevy.

They seem so simple.  Conductor, insulator, gap, threads.  But as we all know, it ain't.

Sonic said:

Agreed, NGK seems to be the answer for most things.  The NGK iridium is basically my go to these days.  

Ironically, they make the early Duratec Focus's run like garbage. Copper 103s FTW.

Aaron_King said:

On T5 and T7 SAABs, from my understanding, you need to use NGK plugs because somehow the ECU used those for knock sensing.  Anecdotally, I have always used NGKs, clean and regap them every oil change and have never had one of the infamous DIC failures that seem to plague SAABs.

The SAAB Trionic system:

https://en.wikipedia.org/wiki/Trionic

one of the first ion sensing ignition system on a production car. The system puts a low voltage over the spark plugs when they are not fired to measure ionization in the cylinders. The ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire measurement function.

There's a lot more to modern ignition systems than just coils and plugs.

There's also things like older Chrysler 2.2/2.5L turbo motors tended to blow the platinum off of those plugs and have it ping-pong around the cylinder.  Basically they work perfectly fine with Champion or NGK copper plugs.  It wasn't a particularly fancy ignition system, but something about the combustion chamber pressures/temperatures/shapes consistently caused issues.

Stefan (Forum Supporter) said: The system puts a low voltage over the spark plugs when they are not fired to measure ionization in the cylinders. The ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire measurement function.

That's cool, but it sounds like an exquisitely undependable way to detect any of that stuff in a real, production application. Slide rule in one hand, bong in the other...

My Mazda used to *eat* sparkpugs. And it only ran properly on one particular type of NGK. And probably because that thing ran on the very ragged edge of detonation, it would  crack an insulator on at least one of them (at random) every 15k or so. I leanred not to ask it silly questions like "why just this plug and how and why do you keep breaking them" and just put a new set in when it started to misfire. 

All the older Fords I've owned that had a TFI ignition hated anything other than Motorcraft stuff. The '95 F150 had the stupid Bosch Platinum +4 plugs and parts store brand wires and distro cap/rotor when I bought it. It had a bad cold miss and the fuel mileage sucked. I replaced everything with Motorcraft parts and it ran much better and gained 2mpg.

I dunno why it works but it does.

It's some strange black magic for sure. I've had good luck with NGKs in almost everything, but I'll usually stick to oem if I can. Acdelco for chevys, motorcraft in the fords, Bosch in the VWs, NGK everywhere else. I don't touch champion plugs, but I don't do dodge so I have no need. 

In reply to (Jesse) Ransom :

I know the old school air-cooled vw bugs are picky do to super low compression.

As least that's what my dad tells me.  And if he doesn't know who does?

In reply to (Jesse) Ransom :

I wonder how much is monkey see, Monkey do?  Somebody changes worn out plugs with a different brand and that's the best brand!?!?! 
I used to play the heat range game I'd need a little hotter plug because I was  running rich. Or leaded fuel. Whatever. Or I'd get a load of race gas that needed a colder plug to keep from preignition burning things.  
different camshafts, different carb settings different timing. Heck I had to have some knowns. I could read a Champion and see what the engine needed. 
I've tried brands other than Champion and just didn't have the same comfort level with. NGK, BOSCH,  AC didn't matter  the fire ring would be in a different spot on the electrode, or different color, whatever.  One brand would have little blisters that showed up under the eye lope  or need a change in plug gap to run smoothly.  

I know my 80's BMW's and VW's would not run right unless they had Bosch copper plugs and I remember my 60's Mopar's only seemed to like champion plugs.

I experienced one really weird plug selection issue. The late Jeep 4.0 inline 6 seem to run better on Autolites than Champions. I thought that it was pure internet hogwash until I was trying to solve a miss on a Wrangler. Sure enough, it ran like crud until I installed Autolites.  It is bizarre. 

I've only had one engine that was particular about plugs. I had a Liberty that wouldn't run on anything that wasn't copper. Platinum plugs would make it misfire at idle. 

Everything I have currently has platinum plugs in it. I change then when I buy the vehicle and usually never touch them again unless they cross 100k miles.

In reply to Stefan (Forum Supporter) :

Thanks for that, I have had Trionic cars for 17 years or so and never bothered to look that up.  Its interesting to me that that system tried to simplify things, fewer bits to break.

My civic has had weird issues with eating plugs every 6 months or so that I ended up just buying the cheapest NGKs and replacing them when the misfires came back. Though I am starting to wonder if my issues were from the distributor as it recently seized up on me and I had to replace that, and upon start up car ran much better than before, so I'll be seeing if my random misfires come back...