spark plug gap

[mrscullini]

did a search and to my surprise not one thread with a gap spec.

the emissions label says 062 to 068, this seems huge, the owner's man say 052 to 056. i can't remember what i did last time. which is it?

is the 062 spec some california bs?

 

[Bob Ayers]

What engine do you have?

 

[Big Jim M]

The purpose of the gap being larger or smaller is to make sure there is a combustable mixture in the gap when the spark occurs.. A SMALLER gap taxes the coil less using less voltage to jump the gap. As long as the engine doesn't MISS use the smaller of the choices... A LARGER gap has no use whatever if the smaller one doesn't cause missing from lack of mixture..
Big JIm

 

[mrscullini]

What engine do you have?

sorry, minor piece of info missing.

'02 4.0l sohc, 141k mi.

 

[gotmudd]

The purpose of the gap being larger or smaller is to make sure there is a combustable mixture in the gap when the spark occurs.. A SMALLER gap taxes the coil less using less voltage to jump the gap. As long as the engine doesn't MISS use the smaller of the choices... A LARGER gap has no use whatever if the smaller one doesn't cause missing from lack of mixture..
Big JIm

the increase in plug gap is because todays motors use a "HIGH ENERGY" ignition system to produce the spark. the purpose of the the increased gap is so that you get a hot enough spark to your plugs to produce the proper detonation. follow your owners manual unless your manual specifies to follow the VECI label. and FYI Big Jim, it don't matter how much gap your plug has, THE ENTIRE CHAMBER has what you refer to as a combustable mixture,without the proper gap it will run like a turd.

 

[Big Jim M]

Gottmud Maybe you need to read up on fuelies a little more.. Sparks and coils did fine as long as the mixture from carbed engines was as rich as it was.

When injection came to the front the mixture was sometimes so LEAN that there wasn't fuel in the .032 gap.. And the engine would stumble a little so it was needed to put a wider gap in the sparks to make sure there would be enough fuel in the GAP to start the fire..

This wider gap needs more power to jump a spark.. So in turn "hotter" coils need to be used.

The POWER of a coil is only needed to make the spark EXTRA power is never used.. coils build up until the spark happens.. If it takes 21,000 volts to make the spark, having a 80,000 volt coil is having bout 40,000 volts that NEVER get used.

Guys purchase huge racing coils all the time thinking they have helped something in their vehicle..WRONG! If the present coil fires the plugs..No new coil will out preform it.

Guys also wide'n the gap thinking they have done something...if the present gap isn't causing a miss here and there then a wider gap won't do anything except require the coil to work harder..
Big JIm

 

[Big Jim M]

By the way... The fuel mixture doesn't care a hoot how "hot" the spark is! A small yellow spark will light the mixture in the same amount of nano seconds, and the explosion is the same no matter how it started.
All these things in the chamber happen in the blink of an eye.. It is an explosion for gods sake! Once started it don't know what started it.
The demos on the counter at the parts house are for the UNINFORMED!
Big JIm

 

[MAKG]

I agree with the gist of this.

However, it's not an explosion. It's a burn. It makes a nice smooth pressure curve. That is, unless there is a shock wave in there (due to multiple flame fronts or whatever). THEN it's an explosion (detonation/pinging/spark knock).

It's amazing how often it's misunderstood, but the point of combustion is ONLY to heat the air (plus add some volume of water vapor and carbon dioxide). If you could heat the air the same amount by other means, it would work pretty much the same. Pistons don't move by shock waves; they move by the expansion of heated air. Or they break.

Another way to think about lean misfires is that there have to be at least a few fuel droplets in the spark gap to fire it off. If you widen the gap, you get more in proportion. If you make the mixture richer, likewise.

Anyone who has been close to a large firework can tell you the difference between a detonation and a deflagration. The SAME burn happens, but one of them whacks you in the chest and the other doesn't.

 

[mrscullini]

i still don't see a gap spec, hahaha.

no worries, i went with about 053. check the comp in each cylinder, range between about 160 and 170. i figured not bad for 141k.

question about the coil pack, the back row is 1, 2, 3 left right. the front row is 5, 6, 4 left to right. at least this is the way mine is. is this correct?

seems to run/idle fine, no misfires or lack of fires. keeping consistent, it seems 4 and 6 or 5 and 6 should be swapped.

02 4.0l sohc.

 

[MAKG]

The coil pack has the cylinders labelled on it. Clean the crap off it.

 

[shadetree]

With lean burn engines, as most modern engines are, the lean mixture is slightly harder to ignite. Most also have some kind of swirl to insure a good mix of fuel/air, so the amount of fuel in the combustion chamber is the approximate same no matter where it is, spark plug gap, or somewhere else. The larger gap requires a higher voltage to jump the gap due to increased resistance in the circuit, hence, more energy to light off the lean mixture.

And, Gross is right, it is a burn not an explosion. In fuel burning dragsters, it is an explosion, not a burn. One mistep results in much damage. shady

 

[Bob Ayers]

The larger gap requires a higher voltage to jump the gap due to increased resistance in the circuit,

Wrong, a 0.050" air gap has the same resistance as a 0.032" air gap (infinity=infinity). The wider gap needs a higher voltage for the ionization field (spark) to take place.

Combustion is a lot like being pregnant, there is no such thing as a little bit pregnant.

 

[Bob Ayers]

According the Motorcraft website, the correct plugs for your truck are AGSF34FP, and the correct gap is 0.065.

 

[Bruce]

Yep thats the plug(AGSF34FP) i just took out of my 2002 Ranger and i put XP5144 Autolite in it which is the Iridium plugi gapped them at .060.

 

[shadetree]

Wrong, a 0.050" air gap has the same resistance as a 0.032" air gap (infinity=infinity). The wider gap needs a higher voltage for the ionization field (spark) to take place.

Your stupid arrogance and condescension aside, you are omitting the resistance created by cylinder pressure from compression. I'm not talking about the damn air gap with the plug out of the engine. I'm talking about what the circuit sees in order to create enough voltage for the spark to jump the gap.

Combustion is a lot like being pregnant, there is no such thing as a little bit pregnant.

Whatever this is supposed to mean, it doesn't make sense.shady