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POLL - Regapped Sparkplugs = ± MPG?

  • DEFINITE increase in MPG ( ++ )

    Votes: 9 15.3%
  • SLIGHT increase in MPG ( + )

    Votes: 19 32.2%
  • No DISCERNABLE change in MPG ( 0 )

    Votes: 19 32.2%
  • SLIGHT decrease in MPG ( - )

    Votes: 1 1.7%
  • Too EARLY to tell ( ? )

    Votes: 11 18.6%
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Discussion Starter · #1 · (Edited)
Regapped Sparkplugs = ± MPG?

OK, what's the "running" verdict on regapped sparkplugs yielding improved fuel economy?

We'll leave the question as to "...increased HP?" for later.
 

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I'm playing with octane now. I borrowed a ODBII Bluetooth interface and installed Torque Lite on my android phone. At 89 octane I have no Knock Retard occuring and the car feels the same way it did on 91 octane before I regapped. I'm now testing 87 octane. If I have no KR at 87 I'll also test 85 octane. Because of the lower air pressure at altitude engine knock issues drop making lower octane feasable. Just being able to run 89 instead of 91 will pay for the regapping in one full tank of gas. I'd call that a pretty good return on the $2.15 investment I had to make to purchase a wire gapper.

As for increased MPG, there are several stretches of my daily commute that I had to be in 5th gear. I can now drive those same stretches in 6th gear. This should improve my MPG because I'll be running at a lower RPM, but I don't know by how much yet.

This is for my ECO MT. I haven't regapped my son's LS MT yet.

Question - can we go back and change our answer to the poll later? I'm currently marked as "Too early to tell."
 

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Discussion Starter · #3 ·
Question - can we go back and change our answer to the poll later? I'm currently marked as "Too early to tell."
If one of the Moderators or Admins will be so kind as to go change it, "Yes," but I can't change it now.
 

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2 mpg increase, as verified by the DIC and ScanGauge II. Went from 45 mpg DIC to 47 mpg. Same routes, similar/worse weather (using A/C more), and needing to play catch-up a few times. SGII went from 43 mpg to 45 mpg. It's there for me. Might not be as discernible for others.
 
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My fuel economy is down 2 mpg, but I'm using the air conditioning now, so who knows?
My fuel economy goes down 3-4mpg for every tank that I have to use AC for at least 50% of the driving.

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Impossible for me to really tell, as I drive a different route each day. Also, my spark plug gaps were not as far out of spec as most others. Regardless, my average mpg's per tank seems to still be going up, even after 18,000 miles and 6 months of ownership.
 

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2 mpg increase, as verified by the DIC and ScanGauge II. Went from 45 mpg DIC to 47 mpg. Same routes, similar/worse weather (using A/C more), and needing to play catch-up a few times. SGII went from 43 mpg to 45 mpg. It's there for me. Might not be as discernible for others.
So ... what gaps are people using in order to see this mileage improvement? I haven't messed with plug gaps yet, but DID notice improved mpg when switching from lowest octane available to highest octane available in my area ... about a 4-6 mpg increase, which more than pays for the extra 20 cents per gallon for the highest octane!
 

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Discussion Starter · #11 ·
...0.035" instead of 0.025" roughly, unless they've had their ECU reprogrammed for performance by Vince or someone else.

...spaycace -- curious, how do you pronounce it: space-ace or what?
 

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OK - I don't have any appreciable change in MPG, but I was able to save 25-30 cents per gallon by dropping from 91 to 87 octane with no drop in MPG or overall performance. Basically the cost of the plug gapper will be more than covered in one tank of gas.
 

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Mine was down 1 MPG on my first tank but I also noticed myself above 4k rpms a lot during takes offs since its do smooth now and I had lots of 72 - 75 MPH driving instead of my normal 65. I will go back to my normal driving habits on this tank and I will post back up in 5 days or so. I am expecting 37+ out of it.

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OK. This improper spark plug gap setting on many Cruze engines is a fantastic find. Now we should ask WHY spark plug gaps are not being set properly during vehicle assembly. One possibility is that time factors during assembly are being squeezed to the point that some assemblers are NOT gapping spark plugs properly, while in a hurry. Anyone have input into the seemingly simple ability to gap spark plugs properly?

Seems that experienced assemblers could almost visually see that spark plugs are not gapped properly between 0.025" & 0.035".
 

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Spark plugs are supposed to come correctly gapped. The people assembling the car shouldn't have to check and regap the plugs before assembly. In this case, however, I think it would be in GMs interest to set up a spark plug "regap line" before the plugs actually get the the car assemblers.
 

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OK. This improper spark plug gap setting on many Cruze engines is a fantastic find. Now we should ask WHY spark plug gaps are not being set properly during engine assembly. One possibility is that time factors during assembly are being squeezed to the point that some assemblers are NOT gapping spark plugs properly, while in a hurry. Anyone have input into the seemingly simple ability to gap spark plugs properly?

Seems that experienced assemblers could almost visually see that spark plugs are not gapped properly between 0.025" & 0.035".
 

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Discussion Starter · #19 · (Edited)
OK. This improper spark plug gap setting on many Cruze engines is a fantastic find. Now we should ask WHY spark plug gaps are not being set properly during engine assembly. One possibility is that time factors during assembly are being squeezed to the point that some assemblers are NOT gapping spark plugs properly, while in a hurry. Anyone have input into the seemingly simple ability to gap spark plugs properly?

Seems that experienced assemblers could almost visually see that spark plugs are not gapped properly between 0.025" & 0.035".
...the OEM supplier (NGK) is supposed to be delivering them already pre-gapped to GM specifications; they are not being "gapped" individually as each one is installed in each engine on the production line.

...but, that also begs the question: where's the GM Quality Control "inspections" which are supposed to be ensuring that everything is "...per specifications & tolerances..." before things leave the factory?
 
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...the OEM supplier (NGK) is supposed to be delivering them already pre-gapped to GM specifications; they are not being "gapped" individually as each one is installed in each engine on the production line.
You bring up a point now that I am trying to get to. Yes, I'm sure plugs are being pre-gapped & probably accurately to GM specs. I think after the plugs are placed in their boxes & shipped, the jouseling & banging they are receiving might be tapping the plugs down to under 0.3". I would think that plugs should be gapped by the assembler himself or as you say, a pre-assembler, while on the line.
 
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