How Important is Spark Plug Gap???
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Post Fiend
Joined: Oct 2003
Posts: 9,176
Likes: 4
From: Western Central NV
How Important is Spark Plug Gap???
I found out today Spark plug Gap isn't very important. I changed the Plugs in my 95 F150 4x4 302. To my surprise the plugs in it were the original factory plugs. They were never changed since new. This truck has 138,400 miles. Since changing the plugs I notice no difference in performance or starting. With the OEM plugs I got 19.5 mpg. @ 65 mph this truck has a 5 speed. Monday I will see if I gained or lost mileage with new plugs.
I won't tell you guys the gap on the original plugs right now. I want to hear what you guys have to say & what do you think the plugs gap was?
Craig
I won't tell you guys the gap on the original plugs right now. I want to hear what you guys have to say & what do you think the plugs gap was?
Craig
Lead Driver
Joined: Dec 2012
Posts: 7,877
Likes: 49
From: Tennessee
The wider the gap past spec , the harder the ignition system has to work . The gap , is a set point . That gap will expand with with wear . A tiny bit gets worn away with each plug firing . Too small a gap can also cause issues just as too wide a gap . That said , modern ignition systems are much more forgiving than old point systems . I have seen .080 or more on worn plugs , with no complaint .
Last edited by JWC 3; Mar 1, 2013 at 09:50 PM. Reason: decimal point
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Post Fiend
Joined: Oct 2003
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From: Western Central NV
Anyway since you guys took a guess I will tell you. The gap was over 1/8th of an inch. Around .125-.150". I kept on of the plugs & if I get a chance I'll post a picture.
Craig
Fleet Mechanic
Joined: Nov 2007
Posts: 1,993
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From: Colorado
Because if you research you will find a BF42 was the factory plug. They don't even use that number anymore & from the looks & condition of the outside & gap. All the hoses, shocks, suspension parts, exhaust parts are all original.
Anyway since you guys took a guess I will tell you. The gap was over 1/8th of an inch. Around .125-.150". I kept on of the plugs & if I get a chance I'll post a picture.
Craig
Anyway since you guys took a guess I will tell you. The gap was over 1/8th of an inch. Around .125-.150". I kept on of the plugs & if I get a chance I'll post a picture.
Craig
Wanted to let you know I wasn't challenging you. I was curious how you knew, is all. I should have worded it better, sorry.
That s a crazy dang gap. I always keep my last couple sets of plugs, as I think they can tell me a story over time of what is going on in my engines.
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Post Fiend
Joined: Oct 2003
Posts: 9,176
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From: Western Central NV
Wanted to let you know I wasn't challenging you. I was curious how you knew, is all. I should have worded it better, sorry.
That s a crazy dang gap. I always keep my last couple sets of plugs, as I think they can tell me a story over time of what is going on in my engines.
That s a crazy dang gap. I always keep my last couple sets of plugs, as I think they can tell me a story over time of what is going on in my engines.
Anyway all is good here with me.
They were all burning clean. The exhaust on this truck is clean also in fact the end of the tailpipe has a rust color.
Craig
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Post Fiend
Joined: Oct 2003
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From: Western Central NV
If you look up Motorcraft plugs for this truck they call for SP450, (SF42CF4) Autolites are AP25.
Craig
Cargo Master
Joined: Jan 2004
Posts: 3,118
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From: South Dakota
With that kind of gap 138,000 miles would be short I would think. My '94 F-150 had 194,000 miles when I changed the plugs. It had Motorcaft plugs so I thought they were probably the originals. I bought it with 140,000 miles with no known history. Those plugs had a gap of about .090. Starting out at .044. That's how I came up with my confident, but inaccurate, guess under #3.
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Post Fiend
Joined: Oct 2003
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From: Western Central NV
Craig