Chevrolet Cruze Forums banner

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%

POLL - Regapped Sparkplugs = ± MPG?

16K views 51 replies 27 participants last post by  14'ecocruze 
#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.
 
#2 ·
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."
 
#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.
 
#4 ·
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.
 
  • Like
Reactions: DrVette
#10 · (Edited)
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!
 
#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?
 
#34 ·
I pronounce it "space ace" ... some like to say space case. Thanks for the info on gaps though! I'll have to run a few tanks with re-gapped plugs, then increase tire pressures to 40 and see how it goes.

BTW ... my best mpg on a road trip with family of 4 and luggage was 47.7 mpg on a tank. I'm also going to look into whether or not the fuel pump on the eco can be replaced with the "regular" fuel pump so we can fill our tanks to capacity without taking 20 mins to fill up! More to follow ...
 
#12 ·
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.
 
#15 ·
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.

Sent from my SAMSUNG-SGH-I997 using AutoGuide.Com Free App
 
#16 ·
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".
 
#17 ·
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.
 
#18 ·
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".
 
#19 · (Edited)
...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?
 
  • Like
Reactions: obermd
#22 ·
It takes a good bit of force to bend the prong. Doubt that's what's happening.

My gas mileage has DEFINITELY gone up after doing this. I'm getting low 40's on the highway whereas before I was getting 38 or so. This is from an LT as well with shorter gears than an ECO, running AC and driving 75-80 mph (~3000 RPM). Lag under 2000 RPM with the air conditioner on still exists, but it doesn't feel like its going to die when I have to take off from a stop.

Only 3500 miles on mine; hoping the mileage will go up as the engine continues to break in.


Sent from my Autoguide iPhone app
 
#23 ·
After one tank on 87 octane I am getting close to the same performance and MPG as before I regapped while running on 91 octane.
 
#26 ·
I'm pretty sure someone else mentioned this before but I'll mention it again.

Plugs that are "good" for 100k miles as these ones are won't last anywhere near 100k if they start life at the proper spec.

This is being done on purpose. The plug works it's best at the proper spec. However, it also works well slightly under and slightly over spec which is what gives it the long life properties.
 
#27 ·
I can not believe all the stir I caused after I set the gap to .034" in order to fix some issues. I consistently get 38-40mpg and that isn't putting around. It is driven fairly hard on a daily basis. I also have tire pressure at 40psi.
 
#28 ·
I'm done testing 87 vs. 91 octane. During the months of the year that the temperature stays below 70 I can run 87 octane. The rest of the year I need to run 91 octane to ensure low end power. As for MPG, because the 91 octane provides better low end power, it definitely helps my fuel economy because I can run lower RPM. The 87 in the winter will drop my fuel economy slightly, but it will still be as good or better than what I was getting before regapping.
 
#31 ·
Just checked all of mine. All 4 were at .023, even after 20K miles.

Gapped them all .034-.036.

I'll let my wife continue to drive it as she normally does and I'll keep an eye on the DIC over the next couple of months. If that doesn't register any improvement then there is no appreciable improvement.
 
#37 ·
The fuel consumed DIC estimate in my car has definitely gotten better since I regapped to 0.035". Before regapping I was consistently 8-10% high on the DIC. After regapping I'm see less than 5% optimism.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top