how much spark plug gap difference is close enough?
- Thread starter apollo18
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My company truck went in for plugs a month ago- complained about a random miss.........faulty gap.
Bitog logic:
- Don’t check the spark plug gap - despite pretty much all service manuals listing what the gap should be, meaning it should be checked
- Don’t use anti-seize - if manufacturers wanted you to use it, they would say so in the service manual.
- Don’t check the spark plug gap - despite pretty much all service manuals listing what the gap should be, meaning it should be checked
- Don’t use anti-seize - if manufacturers wanted you to use it, they would say so in the service manual.
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- May 31, 2024
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Wider gap = higher voltage, not higher current.
Higher required voltage creates possibility of "leak" (short) to ground before the gap.
Yes it wears out ignition parts sooner. But the engine will probably not exhibit any performance issues.
An old trick to get a flooded vehicle to start, was to pull the plug wires out slightly to get a "hotter" spark.
Higher required voltage creates possibility of "leak" (short) to ground before the gap.
Yes it wears out ignition parts sooner. But the engine will probably not exhibit any performance issues.
An old trick to get a flooded vehicle to start, was to pull the plug wires out slightly to get a "hotter" spark.
People (even mechanics) also forget on a distributor the spark is also ionising and jumping the rotor-to-cap terminal gap. When the timing advances at idle and light throttle, this can be a big 30 deg+ jump and become an .080" and larger gap.
I had problems (spark scatter) with small cap dist V6 vortec engines; sometimes swapping in a NAPA rotor with a semi-circular contact tail would help. Main problem is the dist cap diameter is too small for HEI, terminals are too close together. I actually cut a window in the distributor cap to try and diagnose this spark scatter issue in the 90's with my otherwise stellar and comfy GM 4.3 5 speed W/T. GM and Delco Remy are usually smarter than this. They are Ignition "masters"
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I check every new plug. They're sensitive creatures and if the box was dropped it may have affected the gap. Have you seen the brain trusts that work the parts counters AND shipping warehouses??
I've had RA toss individually boxed (like they broke up two 4-packs to get 6 plugs) plugs in a larger box with heavy items.
I've had RA toss individually boxed (like they broke up two 4-packs to get 6 plugs) plugs in a larger box with heavy items.
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Coil on plug eliminates so many potential problems. I've still seen shorts develop in the plug boot on those.
The Ford 4.6 coils commonly go bad due to that issue.
Spark demand on acceleration rises all on it's own - without involving the advance inside a distributor.
When an engine skips/misfires on acceleration that has always been a symptom to look at the ignition system.
The engine can run fine at steady RPM, but when the spark demand rises - the voltage can rise above the threshold of where the "leak" occurs. Losing the spark elsewhere before the plug gap.
The old AC Delco rotors were famous for burning a hole through the center, and shorting to the distributor shaft.
I remember when some rotors had a resistor built in - for European RFI regulations.
0.001” is about the thickness of heavy-duty household aluminum foil /
I wouldn't even think about adjusting spark plugs by this number.... /
I wouldn't even think about adjusting spark plugs by this number.... /
Just to not confuse the reader, an 0.080" gap in a distributor is not the same as the one inside the engine on a compression stroke-- with 10:1 compression, it's 10x harder to jump a gap inside a running engine.
This is why spark testers have an adjustable gap that goes out to around 3/4 of an inch, to simulate the difficulty of sparking under real conditions.
It's also why waste spark was so successful-- the wasted spark was on a "nothing" part of the engine cycle and very easy to jump, so the spark energy would find work to do on the companion plug under compression.
Modern engines with well designed combustion chambers and efficient ignition systems are light years better than your old small block Chevy or Ford. There is absolutely zero fuel efficiency or reliability to be gained by modifying the stock ignition system. That said, small deviations in plug gap are not going to hurt (or help) anything, but a significantly wider initial gap will reduce the time before the plug gap is too wide to work correctly due to electrode erosion. The wider gap accelerates electrode erosion, too.
I don't think I have ever gotten a set of "Pre-Gapped" plugs that there wasn't at least one or two off a bit.
Observer effect?
I wish I had a time machine. I would love to go back to 1960 and show it to my cousins who used to tune up their own hot roads back in those days of coils, distributors, condensers, and breaker points.
Which specific reader is that?
I was primarily responding to a suggestion of "pulling the plug wires out slightly" to build a higher voltage.Ir plugs and COP have benefited small engine performance greatly along with high flowing 4V cyl heads.
I recall they days of economy 4 cylinder engines; 70 - 80hp slugs from the 80's and then the worst offender the 70's Datsun B 210 Honeybee that was actually about 55 hp on a good day and barely had enough power to move around a parking lot
I liked the waste spark on my wife's older subarus, not so much on Fords. Ford was never very good at making robust, low misfire count ignition systems. My last Ranger 4 banger had iggy problems - along with a full list of other major issues. At FORD quality is job NONE!
Everyone keeps saying Iridium gaps are .043 to 0.044 but neglect the GTDI engines. EcoBoost is 0.028 to 0.031 most are pregapped to 0.030 and many are running .026 to .028 especially with higher boost.
These are Laser Iridiums NGK made to Ford spec, which from what I can tell, are mainly the narrower ceramic insulators at the firing tips.
I found my NGK Ruthenium gapped to .028 became 0.032 after only a few thousand miles. I thought it was the ground electrode being softened from adjusting the gap. I don't see any signs of wear at the electrode tips as they are Ruthenium at the tip and Platinum discs at the ground electrode.
These are Laser Iridiums NGK made to Ford spec, which from what I can tell, are mainly the narrower ceramic insulators at the firing tips.
I found my NGK Ruthenium gapped to .028 became 0.032 after only a few thousand miles. I thought it was the ground electrode being softened from adjusting the gap. I don't see any signs of wear at the electrode tips as they are Ruthenium at the tip and Platinum discs at the ground electrode.
I regularly measure things down to .0005". It's pretty easy to change a small thing in the way you measure, like the angle of the tool you're holding, that could induce an error of a few thousandths on something like a spark plug gap.
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