Spark Plug Gap
- Thread starter Larry
- Start date
Papasonic
Active member
That is where my 1.4 manual trans - non tuned Sonics' plugs were gapped. Prior to checking and adjusting the gap, I noticed that on a cold start, the engine would shudder or wobble some during startup. It just didn't start crisply; like a hesitation and wobble before coming to idle. After adjusting the gap to a non-recomended gap of .030; an increase of just .004 from where they were; I truly feel that the engines' cold starting has improved, and I perceive a little more pull in the lower gears upon acceleration. Now I realize that I wanted to notice a difference, and some may say it's a placebo effect; but I'm pleased with the results; placebo effect or not.
I noticed that on the Chevy Cruze forum; many owners were adjusting their plug gaps to .035 and were experiencing better performance; again, maybe just perceived gains. I would at least set them to the current spec, and experiment some if you feel the need.
Papasonic
Considering most N/A engines come gapped between 0.038" - 0.045", it's no surprise that we have rough idles and poor throttle response.
CyberGreyTURBOZ
New member
I just checked mine tonight and had readings of #1: .021, #3-4: .026. i gaped them all to factory .028 specs, but after reading more i guess i might pull them back out and bump up to .030 or something in that ball park. It wouldn't take long to do it again after i just did it once and figured it all out first time. I took pics and plan on posting a few if nobody has done a how to page yet. Also a few of my plugs had a small amount of carbon and smelled like gas as well as looked wet. The car has not been started in 3 days so maybe a bigger gap will help burn the fuel better.
The plugs looked like that because it's not burning all the fuel, the excess fuel is coating the porcelain and creating soot in the exhaust.
0.028" officially. If you're stock you can go a little higher, but Trifecta recommends 0.028" for their tune.
Officially 0.028", but on cruzetalk they've had success up to 0.035"
Bogus
Senior Member
Really? What kind of success? Better MPG, power, etc.?
All of the above.
theenico
New member
Has anyone actually done before and after dynos on a car with .028 plugs vs .030 or greater?
From what I gathered on the Cruzetalk discussion, it's all butt dyno reports. I'm not saying that there isn't a potential benefit, but no one has provided any truly scientific data and documentation.
From what I gathered on the Cruzetalk discussion, it's all butt dyno reports. I'm not saying that there isn't a potential benefit, but no one has provided any truly scientific data and documentation.
Unless there is a very significant difference in gap, you won't see any gains. The "gains" are in drivability, idling, gear shifts, fuel economy, etc.
CyberGreyTURBOZ
New member
After pulling the plugs the first time and setting all at .028 the next morning i did it again real fast and changed the gap to .032. I have been driving it like that for 2 days with no issues and i have tested thoroughly and not had any spark issues. I can't say if it did anything since i have no physical proof, but i do think it runs better than it did with the improperly gaped plugs. It might be a bit more responsive, but I was not able to drive it right before and after the change to really see an effect. I will be taking it down to cedar point this weekend so i will check my mileage and see how it does. I also plan to take a few back out in a week or so and see if they are cleaner than they were the first time.
I also documented the change with High Rez pictures from my new camera.
I also documented the change with High Rez pictures from my new camera.
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dvn
New member
I re-gapped mine from the factory .026 to .035 as that seems to be the sweet spot for a stock tune over on Cruzetalk. I have to say there is a very noticeable increase in low rpm throttle response! I never understood how guys were getting away with shifting below 2k to achieve mpg as mine was pretty gutless down there. Now I can see it. Pulls much better down around 1.5k. I have also taken it to redline with no spark blow-out. Jury's still out on mpg improvement but time will tell. If I tune I might have to tighten it up a bit but very pleased so far. 
Papasonic
Active member
One concern I have about increasing the plug gap beyond specs is this: Is the ignition coilpack capable of the increased secondary output voltage demand? And if so, for how long? The wider the gap, and the more combustion pressure within the cylinder; (engines with a tune), demands higher coil output. This must be what some are referring to as blowout; experiencing a misfire with too much gap.
I have already experienced a coilpack failure with my 1.4 with a stock tune. I'm just wondering if the reason the factory plug gap seems to have a tighter than customary specification is that the ignition coilpack may be just marginal for its application. (Adequate, but nothing more)
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Papasonic
I have already experienced a coilpack failure with my 1.4 with a stock tune. I'm just wondering if the reason the factory plug gap seems to have a tighter than customary specification is that the ignition coilpack may be just marginal for its application. (Adequate, but nothing more)
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Papasonic
The stock coilpack is probably junk, which is why even with proper gap and fueling you still get a hint of misfire at idle, hesitation, etc. It's just a low-grade coilpack. For the longest time I swore I had a vacuum leak, because when I first crank the engine in the morning it bounces from 1200rpm to 1500rpm a few times. But it is also a sign of improper gap, so I check my gap and it was incorrect. Ah Ha! I thought... It's better, but still misfires and shakes at idle. The only thing I can think of is the coilpack.
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LS1notFOUND
New member
usually stock coils are better than what you find in the aftermarket...usually and GM rarely has problems with them...well in the V8 world anyway.
Also, the coils will fire, what ever they fire, regardless of spark plug gap, your not putting anymore strain on them opening the gap because it not really a draw, just a "shot of lightning looking for [a] ground". Honestly the batteries and charging systems in these little cars is more likely to blame for idle issues.
Another big thing that most likely effects the idle is EGR and other emissions bits trying to keep it clean. Its harder on the ignition system for part throttle and low RPM medium load situations than anything else. This is because under Wide Open Throttle (WOT) situation you are getting the cleanest air with the best fuel delivery, everything else is designed to have the air from the tail pipe cleaner than that of what enters the air box.
Combine that with possibly really leaned out idles and you just might not get a complete combustion cycle out.
Heck you may also notice better performance/idle at the beginning or end of fuel tanks. This is because with each fill your fill trims reset to readjust to the new fuel.
Try changing gas stations for the hell of it.
Also, the coils will fire, what ever they fire, regardless of spark plug gap, your not putting anymore strain on them opening the gap because it not really a draw, just a "shot of lightning looking for [a] ground". Honestly the batteries and charging systems in these little cars is more likely to blame for idle issues.
Another big thing that most likely effects the idle is EGR and other emissions bits trying to keep it clean. Its harder on the ignition system for part throttle and low RPM medium load situations than anything else. This is because under Wide Open Throttle (WOT) situation you are getting the cleanest air with the best fuel delivery, everything else is designed to have the air from the tail pipe cleaner than that of what enters the air box.
Combine that with possibly really leaned out idles and you just might not get a complete combustion cycle out.
Heck you may also notice better performance/idle at the beginning or end of fuel tanks. This is because with each fill your fill trims reset to readjust to the new fuel.
Try changing gas stations for the hell of it.