is there an objective DIY spark plug test?

[friendly_jacek]

When one reads spark plug reviews, people say the engine runs better with new plugs. While some of that could be due to better gap in new plugs, I'm afraid some of that is placebo, like better running engine after oil change.

Now, I understand that one can measure firing voltage via oscilloscope. Is there a simpler objective test?

 

[friendly_jacek]

I got it, the answer is: no.

 

[Gokhan]

Originally Posted By: friendly_jacek
When one reads spark plug reviews, people say the engine runs better with new plugs. While some of that could be due to better gap in new plugs, I'm afraid some of that is placebo, like better running engine after oil change.

Now, I understand that one can measure firing voltage via oscilloscope. Is there a simpler objective test?

That's already too simple and won't give you much information. You would have to test them in an actual engine to see if they provide any fuel efficiency, horsepower, or emissions benefits.

I had built some battery-powered high-voltage power supply and hooked it up to a plug. It's fun to observe the blue spark. The idea was to generate microwave radiation -- so, I used a nonresitor plug (without the 5k RF-suppressing resistor inside the electrode) to intentionally generate RF radiation. To build the receiver for the microwave was tricky; so, I didn't pursue it too much.

There has been a lot of research recently for replacing spark plugs with lasers:

http://www.sciencedaily.com/releases/2011/04/110420125502.htm

 

[Vikas]

Either you have complete combustion or not. Once you reach the complete combustion, a "stronger" spark is not going to give you any more advantage. I suppose most of the systems are like that but we being OCD, always think "moar is better"

 

[hattaresguy]

Placebo affect unless the old plugs were so bad they were causing a skip.

 

[friendly_jacek]

Originally Posted By: Vikas
Either you have complete combustion or not. Once you reach the complete combustion, a "stronger" spark is not going to give you any more advantage. I suppose most of the systems are like that but we being OCD, always think "moar is better"


No, there is more than that. Bigger, longer spark = faster combustion = more advanced timing = more fuel efficiency. This is why laser ignition will be in the future (if we still use ICE).

My problem is, can you measure it yourself?

From Denso (not sure how much science and how much advertisement):

 

[Vikas]

Don't quote me but the "bigger longer" spark is essentially determined by the coil and the air gap which needs to jump. Now unless there is insulation breakdown or crack in the plug construction, a fancy plug does nothing more. Better electrode material can resist erosion and keep the shape same.

I do not believe you could compare laser ignition with coil on plug scheme.

 

[bulwnkl]

You can determine burn efficiency relatively simply. Work with Dyson Analysis and be a careful record-keeper. IME you can identify small differences in combustion efficiency if you're careful about what you change and what you control.

 

[RobertISaar]

having to advance timing is indicative of a slower burn speed.

with laser ignition, you'll likely be able to fire a plug far after TDC, nearer the ~14-21* ATDC that is quoted as being the best place for maximum cylinder pressure to occur.

 

[morris]

many many many years ago i experimented a LOT with plugs. i did not learn near as much as thought i would. why? cause i was limited to one engine daily driver. but i DID learn this. 1. if you are making a big change do it on only ONE plug. so if it fails you can get back home. 2. it looks like the spark jumps as far as .25 " from the violence in the chamber pushing the spark. 3. a .010" wider gap will make the plug look like its 1/2 a heat range hotter. 4. surface gap plugs will easily foul out with to much gasoline. 5. surface gap plug likes propane fuel.

 

[SteveSRT8]

Originally Posted By: Vikas
Either you have complete combustion or not. Once you reach the complete combustion, a "stronger" spark is not going to give you any more advantage. I suppose most of the systems are like that but we being OCD, always think "moar is better"


Exactly. Modern ignitions are extremely reliable and nearly never misfire. They will quickly set a code if they do.

Spark requirements vary vastly from engine design to engine design. There is no one perfect plug. And any gains from amazing new tech are likely to be quite small no matter the tech...

 

[PandaBear]

If you have some OBD / CAN tool that you can read the individual cylinder's misfire rate, you can check the before and after, that'll be easier than using a scope at a precision controlled load / temperature / throttle.

Most of the great feeling people get are not placebo, but the sharp edges of a new plug over a worn out old plug.

In addition to gap and coil, the firing edge sharpness and electrode diameter also make the difference. Material difference usually only means you can tolerate the stress and make the tip finer.

 

[friendly_jacek]

Originally Posted By: PandaBear
If you have some OBD / CAN tool that you can read the individual cylinder's misfire rate, you can check the before and after, that'll be easier than using a scope at a precision controlled load / temperature / throttle.

Most of the great feeling people get are not placebo, but the sharp edges of a new plug over a worn out old plug.

In addition to gap and coil, the firing edge sharpness and electrode diameter also make the difference. Material difference usually only means you can tolerate the stress and make the tip finer.


Good point about the misfire rate. I took a screen shot from my OBD2 tool while the car idling with bosch +4, but it didn't include the misfire rate. I doubt there is any as the plugs have only somewhere 4000-9000 miles. I'm planing to capture similar data after the plug swap to Denso TT. Since I have the data on MAF, RPM, and injection volume, I should be able to see if there is any improvements in fuel efficiency at idle.

 

[friendly_jacek]

The misfire rate was 0 on all cyllinders. I have pre and post screenshots from Techstream while idling. Minimal differences, but the idle RPM went up slightly making idle a bit noisier. Not sure what it means.

I'm relived the +4 are gone as they seem to lose ground electrodes from time to time.