Just changed the spark plugs

[BaDave]

Did they also teach you how to fix the plugs that blow out of the expedition motors.lmao @ fords

 

[Howard]

Feels like the low-end torque went up...

 

[Raduque]

Originally posted by: Pacfanweb

SO,
NEVER LET YOUR COIL DISCHARGE WITH OUT A CONTROLLED GROUND PATH!
Test plug made from an old spark plug and a piece of wire is fine, don't pull plug wires or coil wires...

This reminds me of something my dad used to do while working on his older cars "Here son, hold this (wooden handled) screw driver (with the plug wire from the distributor stuck on the tip of it ) near the fender while I crank it and tell me if it sparks" He cranks the car, I jump two feet in the air. Only got me once.

 

[jagec]

Originally posted by: Iron Woode
hotter spark means more intense and that means more current. Voltage is fixed by the coil and so is current. Your point is valid but its moot. There is a difference between factory gap specs and an engine's optimal gap. Any improvement from an increased gap will be short lived.

I dunno, this isn't really my specialty, but it seems to me that if the plugs are getting no voltage at one time, and full voltage at another, it has to have a finite rise time and fall time, unless the entire system is superconducting (yeah right). When the primary winding in the coil is disrupted, the collapsing field will induce a rising voltage in the secondary winding. Once this voltage gets high enough to jump the gap across the spark plug, it does so. Well, if the gap is larger, the voltage will be higher by the time it's able to fire (That means the spark will be slightly retarded, but it shouldn't be a big enough difference to matter). I can't say for sure what this would mean for amperage, though...I could well imagine that the smaller gap actually has a higher-amperage spark. Still, if the larger spark ignites more molecules of gasoline and inhibits less of the flame front, it could well lead to a cleaner burn.

I don't see it as making a huge difference in mileage, but you can't claim that nothing will change.

 

[Pacfanweb]

Originally posted by: jagec

Originally posted by: Iron Woode
hotter spark means more intense and that means more current. Voltage is fixed by the coil and so is current. Your point is valid but its moot. There is a difference between factory gap specs and an engine's optimal gap. Any improvement from an increased gap will be short lived.

I dunno, this isn't really my specialty, but it seems to me that if the plugs are getting no voltage at one time, and full voltage at another, it has to have a finite rise time and fall time, unless the entire system is superconducting (yeah right). When the primary winding in the coil is disrupted, the collapsing field will induce a rising voltage in the secondary winding. Once this voltage gets high enough to jump the gap across the spark plug, it does so. Well, if the gap is larger, the voltage will be higher by the time it's able to fire (That means the spark will be slightly retarded, but it shouldn't be a big enough difference to matter). I can't say for sure what this would mean for amperage, though...I could well imagine that the smaller gap actually has a higher-amperage spark. Still, if the larger spark ignites more molecules of gasoline and inhibits less of the flame front, it could well lead to a cleaner burn.

I don't see it as making a huge difference in mileage, but you can't claim that nothing will change.

That's actually a really good description of what happens there. And no, it won't make a HUGE difference in mileage, but even 1 mpg you'd notice. Think about it: Get 1 mpg more or less, and that's 20+miles either way out of a tank in any SUV or truck.
And you definitely can make a difference on certain cars by tuning the plug gap, if you so choose.
Lots of people have...there's lots of info out there to be had that shows how they did it.
That's all I was ever saying before this got off on the technical side.

 

[Blunc]

I have a few cents to add to this discussion.

jagec is basically correct regarding the "mechanics" of the electrical side of ignition, I would add that for quite a while (from the mid-seventies) GM HEI (which could generate 100KV sparks) regularly spec'd plug gaps wider than the previous standard of 0.30" or 0.35", some as wide as 0.80" on Oldsmobile engines.

I believe this was required due to extremely lean fuel mixture required for emissions and engines with low compression. The wider plug gap exposed more spark to the fuel charge in the combustion chamber. I recall the ignition timing was very advanced during the 1970's and 80's, some as high as 18deg BTDC.

too small of a gap or using a spark plug not rated for the engine use and environment will almost always adversely affect engine performance.

 

[Howard]

I think you're missing a 0 in there somewhere, Blunc.

 

[LTC8K6]

"I think you're missing a 0 in there somewhere, Blunc."

Yeah, now those are some gaps!

 

[Blunc]

Originally posted by: Howard
I think you're missing a 0 in there somewhere, Blunc.

D0H!!!

 

[PandaBear]

Originally posted by: Pacfanweb
That's normal. I've been 90k+ on regular copper plugs. Today's ignition systems can jump a plug gap far larger than the factory spec.

The ignition system has to discharge a bigger/hotter spark to jump the big gaps, so your gas mileage will tend to increase as the gaps get bigger.
I will say that the increase isn't as dramatic with today's OBDII systems and distributor-less ignitions as it used to be.

I remember in the early 90's when the Explorers came out. They had platinum plugs, good for 60k. So I did a few, and other guys in the shop did them when they started hitting that mileage, and customers started coming back a couple weeks later complaining about reduced fuel mileage since the tune up. Reason was, the gap had gotten large enough to create a really big spark, and the combustion was better.

It will lose some fuel economy and it runs rough, plus put more stress on the coil and that thing is expensive ($50-120 depends on where you get it). If you don't have to take out the intake manifold (FWD V6), then just change it every 30k, it is a cheap insurance.

 

[PandaBear]

Originally posted by: LTC8K6
The coil has no clue what the gap is and it generates the same voltage all the time.
The fact that that voltage will also jump a larger gap, doesn't mean that it's better.
If a larger gap would work better, the mfg would use it.

E = V/d. The E (electric field) stays the same and if you increase the d (gap), V (voltage) increase.