Spark plug gap - what does it do?

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I have an 01 sable with the duratec motor. The manual says to gap plugs from .052 - .056. I have heard that a wider gap gives better highway fuel efficiency but is harder to start especially in colder weather. Just curious what some thoughts are on this as I may do some testing. How small or large can the gap really be set and still perform ok?
 
I can tell you from my own experience that I have had turbocharged engine misfire badly in the upper rpms with too wide of a plug gap. After this happened I typically gap on the lower end if a range is given. You could probably adjust the gap one way or another until you can sense a decrease in performance.
 
Go with what the factory recommends. A wider gap makes a hotter arc and your plugs will wear faster as the gap increases.
 
I gap in the middle of the range. Remember, as the plug wears the gap will open naturally. I wouldnt worry about the turbo thing unless you have one. Tts a known issue with all types of forced induction. The higher cylinder pressures increase the voltage requirement to jump the gap. Since the same ignition system is typically used, the gap is made smaller to compensate. Such as .032-.034
 
If you gap plugs. (Lots of Platinum, Double Platinum, and Iridium plugs you DO NOT GAP.)
Gap towards the smaller end of the range.
As the spark plug wears that gap will enlarge.

There is resistance in a plug, hence the arc, and the timing of the engine is directly related to it. Play with that gap too much and you will get pre-detonation (ping), or a late/no spark situation.
I haven't played with spark plug gap since my 1983 Ford LTD died. Everything else took Platinum pre-gapped plugs and was computer controlled.

Computers and solenoid packs take a lot of guess work out of timing an engine. Don't know when the last time I used my timing light was.
 
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Two things determine the gap at the plug: 1) the voltage that the coil generates, and 2) the engine compression.

Higher compression makes it harder for the spark to jump the gap. If you widen the gap without changing the ignition voltage, you can certainly get misfires. You can always narrow the gap, but at some point you're not "exposing" enough spark to the air/fuel mixture to get reliable ignition.

So bottom line- go with the factory spec, or narrow it by a few thousandths knowing that the gap will widen as the plugs wear. A little on the narrow side is safer than a little on the wide side.
 
Not gapping Iridiums/Platinums are a thing of the past. As long as you're careful, no reason to not re-gap to fit your needs.

50% of the time, gaps are not correct anyways.

Cheers!!
 
The gaps on most of the iridium plugs I have bought have too large of a gap.

I usually gap it slightly less than OEM so I have to check them less often.
 
I bought Denso TT Platinum plugs that come pregapped at .040 when my car say it should be .052-.056. I have set them as close to .052 to .054 as I can. Sure would be nice to have a tool that would set it a little more accurate than bending with plier and checking. Also did not want to damage the electrode or arm.
 
Lots of information and misinformation above.
Of course you can and should check and adjust the gap on ANY plug type. If you are a clod, you are a clod. But you would still be a clod with old plain steel plugs.
I like biasing my plugs toward the wider side of the gap range. A bit better for lean conditions.
I actually go over .005" or so as normal in my own vehicles.
In a good ignition system, there is a lot of latitude.

I don't see how it is physically possible to make an engine 'ping' by changing the spark gap.
 
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Originally Posted By: spk2000
I bought Denso TT Platinum plugs that come pregapped at .040 when my car say it should be .052-.056. I have set them as close to .052 to .054 as I can.

NGK says they do not recommend opening or closing the gap more than .008 either way. You're exceeding that. Buy the correct plugs for your application.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqgap.asp?mode=nml

Originally Posted By: spk2000
Sure would be nice to have a tool that would set it a little more accurate than bending with plier and checking. Also did not want to damage the electrode or arm.

Pliers are the worst thing you can use. Too fat and too crude.

See this YouTube video from NGK:
http://www.youtube.com/watch?v=lk70oyUEftY
Note the tools the guy shows at the beginning. Those are the correct ones. And they are cheap.

In the chat below the YouTube video, the NGK rep says to tap the plug on a hard surface to close the ground electrode, but I think it's better to use the pry tool on the plug gapper, the same way he uses it to open the gap.
 
I have just driven over 300 miles today in the rain with my Sable. So far I was only able to change the 3 front plugs over to the Denso TT plugs and my fuel economy on this trip jumped from 24-25 mpg to 29 mpg. I can;t wait until I find to to get those back 3 changed and see what I get. When I first bought the car I was able to occasionally get 31 mpg in PA when speed limit was 55 mostly on turnpike. Today I was doing 70 most of the way and did great. Especially with these high prices I am pleased with the results. Are there any negative effects by mixing 2 different plugs for a short while? Is it hard on the engine or coil pack?
 
Originally Posted By: mechtech2
Lots of information and misinformation above.
Of course you can and should check and adjust the gap on ANY plug type. If you are a clod, you are a clod. But you would still be a clod with old plain steel plugs.
I like biasing my plugs toward the wider side of the gap range. A bit better for lean conditions.
I actually go over .005" or so as normal in my own vehicles.
In a good ignition system, there is a lot of latitude.



The gap they give you is a service recommendation. Kind of the opposite of a service limit. They count on it growing over time.
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Originally Posted By: spk2000
I bought Denso TT Platinum plugs that come pregapped at .040 when my car say it should be .052-.056. I have set them as close to .052 to .054 as I can. Sure would be nice to have a tool that would set it a little more accurate than bending with plier and checking. Also did not want to damage the electrode or arm.


Pliers? A gaping tool costs like 3 bucks eh.
 
I have a gap tool thst measures the gap but to get the correct gap my understanding was to bend the electrode independent of the tool. Otherwise you may damage the electrode. It was a slow and painful process so maybe i should have looked for alternative tools to my keyring gap tool.
 
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