# GM's Official Statement Regarding Spark Plug Gaps



## XtremeRevolution (Jan 19, 2012)

As promised, here is the official statement from GM. Tom Read (GM Powertrain Communications) has run this by both GM Service Engineering-the guys who engineer fixes for issues (Detroit), and GM Product Engineering-the guys who designed the motor (Germany for approval. This is about as official as it gets. 



> Hello Andrei,
> 
> In a follow-up to your question regarding the correct spark plug gap for the Cruze 1.4L turbo engine I worked with our product and service engineering teams to get these answers back to you. Feel free to pass this information on to others.
> 
> ...


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## XtremeRevolution (Jan 19, 2012)

My personal comments:

It is worth noting the choice of words when he said "_potential _negative effects." While many on this board are currently running a .035 gap on both 1.4L Turbo and 1.8L N/A engines without issues, each owner needs to decide for themselves what spark plug gap to set their own car to. Many owners who have increased their gap to .030-.035 (non-tuned motors) have experienced immediate and noticeable improvements in throttle response and an undeniable reduction in lag/hesitation/bogging. It is my personal opinion that a reduction in spark plug life is a small price to pay for the improvements in drivability, and the change from .028 to .030-.035 is small enough that ignition coil durability/longevity will not be significantly compromised. 

Not addressed in the above statement is the issue of inconsistency, which continues to cause issues in owners' cars. Regardless of what you believe that your spark plug gap should be, it is recommended that you check them and ensure that all gaps are set to the same dimension. Enough cars have reported significantly off-spec gaps (11% to be exact were under .023), even given the new specification, to make this worth checking. 

In an effort to consolidate and keep things under control, please continue discussion of this topic in the existing threads:
http://www.cruzetalk.com/forum/10-e...6688-your-spark-plugs-gapped-incorrectly.html
http://www.cruzetalk.com/forum/10-engine-technical-discussion/6958-what-your-spark-plug-gap.html

If a moderator believes it is appropriate, please sticky this topic.


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## Bohdan (Apr 28, 2012)

I wonder if having different sparkplug gaps in the engine will cause Piston damage over time. They say that changing there specified spark plug gap may cause potential negative effects. So how come so many engines have different plug gaps with each cylinder. Its like they have assumed that they are all gapped up correctly.


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## XtremeRevolution (Jan 19, 2012)

Bohdan said:


> I wonder if having different sparkplug gaps in the engine will cause Piston damage over time. They say that changing there specified spark plug gap may cause potential negative effects. So how come so many engines have different plug gaps with each cylinder. Its like they have assumed that they are all gapped up correctly.


They did assume, but of course, we've proven them wrong. Personally, it might be possible. With severe variations in gap spec, there might be a difference in how well the fuel burns. Keep in mind, the O2 sensor reads your oxygen levels to determine air to fuel ratio as a collection of all cylinders, not individually, so it is perfectly possible that some cylinders may be running a bit more lean if the gaps are severely out of spec or inconsistent. My suspicion is that this isn't the case though and the piston damage is a result of oil burning.


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## obermd (Mar 3, 2012)

Significant variations in the gap are probably causing a lot of low end power issues that people are reporting as fixed after regapping. Different gaps cause different ignition results in each cylinder. I highly doubt the ECU is designed to handle this situation.

Also, I notice GM came back and gave a gap spread that would cover the 0.025" that NGK claims they were told to supply but doesn't cover the 0.028" spec in the owner's manual. The range GM gave in their answer actually puts the owner's manual slightly out of spec on the high side. 0.6 - 0.7 mm = 0.023622 - 0.027559 in.

Xtreme - thank you for chasing this down for us.


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## deerebilt (Apr 6, 2012)

Thanks for your work xtremerevolution


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## boats4life (May 28, 2011)

Gentleman and a scholar, this one. lol

Good work, Andrei.


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## OnlyTaurus (Mar 20, 2012)

Nicely done, Andrei! GM Service Information has been updated thanks to you.

Ignition System Specifications 
Application

Specification

 Metric

English

 Ignition Type

Coil-On-Plug

 Firing Order

1–3–4–2

 Spark Plug Type

Refer to Electronic Parts Catalogue

 Spark Plug Torque

25 N·m

18 lb ft

Spark Plug Gap

0.7 mm

0.028 in


It makes me wonder if they are going to set out yet another recall(or atleast a service bulletin) to ensure the plug gaps in all the Cruzes are where they should be.


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## The Wolf Wagon (Mar 5, 2012)

As usual, thanks Xtreme for the GM piece of the puzzle!


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## The Butcher (Apr 6, 2011)

Just re-gapped last night to .028 after reading this and I actually think the car is doing the best it's done so far! Initially they were .019 - .022 and I re-gapped to .035 about two months ago. I think the larger gap and all this AZ heat was causing spark blowout at higher RPM's,cause the car felt like it would nose over around 4,000 rpms, now it seems more consistent under heavy acceleration... Thank you for putting in the time with GM to get clarification on this issue!!


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## GoldenCruze (Dec 18, 2011)

> The spark plug gap is determined by many engineering factors including durability. While there may be seemingly short term advantages to changing the manufacturer’s specified spark plug gap there are potential negative effects. We appreciate customer’s desire to improve performance but please know your engine has been engineered to perform optimally with the original manufacturer’s specifications and we do not recommend altering these specifications.





XtremeRevolution said:


> My personal comments:
> 
> It is worth noting the choice of words when he said "_potential _negative effects." While many on this board are currently running a .035 gap on both 1.4L Turbo and 1.8L N/A engines without issues, each owner needs to decide for themselves what spark plug gap to set their own car to.


This is where we could really use more specific information from GM. While we are cautioned not to vary the gap from the engineer's specification, we are not told what the specific negative consequences are. Only that something negative could happen. With that lack of information, we are left to making our best guess about it. While that guess can be backed up by a lot of knowledge and experience, it is still a guess.

The information that we do have is that there is a specified gap. And we also know that cars have left the factory with gaps set all over the place. Given that information, the safest thing to do is to make sure the gaps are set to the specification. Beyond that, we take a chance with using a different setting.

I would really like some specifics from GM about the "potential negative effects" before changing the gap to an unspecified setting.


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## rbtec (Feb 3, 2012)

GoldenCruze said:


> This is where we could really use more specific information from GM. While we are cautioned not to vary the gap from the engineer's specification, we are not told what the specific negative consequences are. Only that something negative could happen. With that lack of information, we are left to making our best guess about it. While that guess can be backed up by a lot of knowledge and experience, it is still a guess.
> 
> The information that we do have is that there is a specified gap. And we also know that cars have left the factory with gaps set all over the place. Given that information, the safest thing to do is to make sure the gaps are set to the specification. Beyond that, we take a chance with using a different setting.
> 
> I would really like some specifics from GM about the "potential negative effects" before changing the gap to an unspecified setting.


I want a TSB for checking/regapping the plugs.


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## XtremeRevolution (Jan 19, 2012)

CruzeEcoBlueTopaz said:


> So my 2012 cruze eco is at 42k miles @ 50k I plan on putting in new plugs. I care about 50-60mph fuel efficiency what should I set my sp gap to 0.6 mm - 0.7 mm ??? Im not concerned about throttle response or acceleration.
> 
> Also I plan on using AC Delco GM brand plugs or are there other reccomended plugs I should be using ?


Not to be rude, but please post this in one of the threads I provided a link to in my second post and I will be glad to respond. I don't want to use this thread to troubleshoot or give advice, but simply to forward what GM has officially said. 



rbtec said:


> I want a TSB for checking/regapping the plugs.


You're not going to get one. Tom Read has already made this clear to me. Considering most of these spark plugs (~85%) are within the correct range and they haven't been able to duplicate this inconsistency, a TSB is not something he believes is necessary.


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## rbtec (Feb 3, 2012)

CruzeEcoBlueTopaz said:


> So my 2012 cruze eco is at 42k miles @ 50k I plan on putting in new plugs. I care about 50-60mph fuel efficiency what should I set my sp gap to 0.6 mm - 0.7 mm ??? Im not concerned about throttle response or acceleration.
> 
> Also I plan on using AC Delco GM brand plugs or are there other reccomended plugs I should be using ?


Good luck.


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## Beaker (Mar 21, 2012)

While they were implementing their dremel tool recall fix yesterday they checked my spark plug gap. .028. So I'm leaving it alone.


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## NYCruze2012 (Jan 16, 2012)

After all info was presented through the various posts and all the threads we had for spark plug gap I went conservatively for .30 and have been very happy with that thus far. At this point is anyone planning on regapping to the lower numbers? Meaning that after GM's statement did anyone make a determination that we should return to the smaller 0.25 to 0.28 gaps?

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## XtremeRevolution (Jan 19, 2012)

NYCruze2012 said:


> After all info was presented through the various posts and all the threads we had for spark plug gap I went conservatively for .30 and have been very happy with that thus far. At this point is anyone planning on regapping to the lower numbers? Meaning that after GM's statement did anyone make a determination that we should return to the smaller 0.25 to 0.28 gaps?
> 
> Sent from my DROID3 using AutoGuide.Com Free App


I've been at .038 for a long time and will gap down to .032 this weekend.

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## hawkeye (Mar 31, 2012)

I was a little hesitant about moving them up because of durability concerns, but had moved them to .034. To be honest, I hadn't noticed much of a difference, and recently my mpg has been worse. I have attributed that to the 95 degree weather. I have even tried premium gas, and haven't noticed any mpg increase. I'm doing a trip to LaCrosse Wisconsin that I made a few weeks ago and saw 37mpg with my ECO automatic. We'll see if the gap lowered down to .029 will make a change. In reality the higher gap probably won't cause any durability problems, but I'm the type that would worry about it.


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## Blue Angel (Feb 18, 2011)

Subscribed.

"potential negative effects" is a very broad statement, and is probably written that way for very good reason. Negative effects could be anything from a perceived "placebo" non-issue to complete engine destruction, though the latter is likely not a concern.

If GM issues an official document admitting an issue with a specification they open themselves up to a world of problems, not the least of which would be customers blaming non-related issues on this spec.

While most of us on this board will (and likely should) know better, Joe average will simply interpret this as an "internal engine problem" and get worried about it, most likely for no significant reason.

I'm not an SME on combustion chamber design, but based on my own limited experience an improper gap can cause rough operation, reduced mileage, increased emissions, increased chance of misfire and/or plug wire damage, and the list will go on and on. Piston or other structural damage is not on that list as far as I can reasonably conceive.

Having said that, I will be checking my plug gaps and would suggest that others do the same. I would imagine if there is a real issue here, that any dealership tech checking plug gaps will simply set them to spec regardless of what they were at, and report that everything was ok under the hood. 

Once again, thanks XR for the bulletin!


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## XtremeRevolution (Jan 19, 2012)

hawkeye said:


> I was a little hesitant about moving them up because of durability concerns, but had moved them to .034. To be honest, I hadn't noticed much of a difference, and recently my mpg has been worse. I have attributed that to the 95 degree weather. I have even tried premium gas, and haven't noticed any mpg increase. I'm doing a trip to LaCrosse Wisconsin that I made a few weeks ago and saw 37mpg with my ECO automatic. We'll see if the gap lowered down to .029 will make a change. In reality the higher gap probably won't cause any durability problems, but I'm the type that would worry about it.


High heat and 87 octane don't mix well with the 1.4T motor. That will hurt your fuel economy alone by a few miles per gallon regardless of other factors. You need to be running 89 octane at minimum during the hotter months. A/C use will also have a significant impact on fuel economy.


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## jtisch (Jun 21, 2012)

I just changed mine last night to .035 and I immediately noticed the bog/hesitation is gone (minus typical Turbo lag). Since it only took about 15 minutes to do I think I will lower mine back down to 30 and see if it is still smooth.

Thanks for the leg work, much obliged!


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## hawkeye (Mar 31, 2012)

I've seen the 89 octane improve my drivability slightly over 87, but my mpg is the same. The 91 and 93 didn't seem to change the mpg, either. In MN, I've been cranking the AC since April, so that isn't the main factor. June and July have been pretty consistently in the mid 80s to mid 90s, and I think that may be the main reason the mpg has fallen.


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## XtremeRevolution (Jan 19, 2012)

hawkeye said:


> I've seen the 89 octane improve my drivability slightly over 87, but my mpg is the same. The 91 and 93 didn't seem to change the mpg, either. In MN, I've been cranking the AC since April, so that isn't the main factor. June and July have been pretty consistently in the mid 80s to mid 90s, and I think that may be the main reason the mpg has fallen.


Here's the concept behind all of this. Hotter air going into the engine will cause it to be more likely to pre-detonate the fuel and cause knock. The engine knows this and has a table mapped to reduce timing based on the intake temperature reading, and it is an aggressive reduction in timing. A reduction in timing reduces efficiency, and lowers your overall fuel economy. It may not be something that you will notice immediately based on how fast the car is or something that will show up on your DIC, but compare the readings at the pump, and you'll see a difference. Increasing the octane prevents knock from occurring in this scenario. If 89 octane improved drivability over 87 octane, it most certainly made a difference in fuel economy. It is almost certain that there were other factors that caused your fuel economy to go down, cancelling out the gain your engine experienced by going up an octane level. 

It is a proven and well-known fact that these engines pull timing both due to KR and due to the IAT spark table as a result of heat. When heat-soaked, the engine may even bog down and feel like a slug. 89 octane will help alleviate this, and 91/93 octane will go a step further. I cannot speak for the difference between going from 87 octane to 89 octane and the difference going from 89 octane to 91/93 octane, but what I do know for a fact that increasing your octane level above 87 octane will have an effect on fuel economy. 

Any affect in drivability will have also have an effect on fuel economy, although your mileage may vary depending on your driving habits and typical route driven.


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## rbtec (Feb 3, 2012)

hawkeye said:


> I've seen the 89 octane improve my drivability slightly over 87, but my mpg is the same. The 91 and 93 didn't seem to change the mpg, either. In MN, I've been cranking the AC since April, so that isn't the main factor. June and July have been pretty consistently in the mid 80s to mid 90s, and I think that may be the main reason the mpg has fallen.


I have found no difference in drivability or mileage between 87, 89 and 93 octane. I've tried them all.


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## sedanman (Dec 10, 2010)

rbtec said:


> I have found no difference in drivability or mileage between 87, 89 and 93 octane. I've tried them all.
> 
> Sent from my Autoguide iPhone app


Bang 1 or 2 spark plugs down to 0.020" and then see if you notice a difference between high and low octane. Especially after the intercooler is heatsoaked.


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## hawkeye (Mar 31, 2012)

The only drivability concern that I experienced was a slight surging sensation on a cold engine under light throttle with 87 octane. It didn't happen after a minute of driving. The 89 octane didn't seem to have the surging sensation--hence slightly improved drivability and no noticeable change in mpg for me. I'm glad some of you are experiencing the mpg increase with the changes in octane, gap, etc., but unfortunately for me it isn't happening. I won't complain about my mpg, overall, because I am satisfied. We'll see if lowering my gap changes the mpg when I drive to LaCrosse this weekend.


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## XtremeRevolution (Jan 19, 2012)

rbtec said:


> I have found no difference in drivability or mileage between 87, 89 and 93 octane. I've tried them all.
> 
> 
> Sent from my Autoguide iPhone app


I've noticed drivability differences are less prominent with automatic transmission equipped Cruzes. The manuals rely more on low RPM power, where you really feel every little difference. You're also generally more aware of how your car behaves when driving a manual, which might contribute to that.


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## obermd (Mar 3, 2012)

XtremeRevolution said:


> I've noticed drivability differences are less prominent with automatic transmission equipped Cruzes. The manuals rely more on low RPM power, where you really feel every little difference. You're also generally more aware of how your car behaves when driving a manual, which might contribute to that.


That's why both my sons learned to drive sticks. It puts you much more in tune with the car and environment around it.


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## danimal (Oct 4, 2011)

What's better for hot weather .035 or .028? Its consistently been 95+ here the past few weeks except for a few days here and there.


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## XtremeRevolution (Jan 19, 2012)

danimal said:


> What's better for hot weather .035 or .028? Its consistently been 95+ here the past few weeks except for a few days here and there.


If you just want to play it safe, go with .028. I don't think air temperature has any effect here.


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## 8141cruzer (Jul 14, 2012)

For what it's worth... I just bought my Cruze LT 1.4L last week (manufactured in June 2012). After reading the discussions and carefully following instructions given to remove and re-gap my plugs, I found them to all be at .025" which is within the GM spec of .6 - .7mm gap. My car has been running fine but I have a 6 sp manual trans so maybe that's keeping it from bogging down as some have noted. Many thanks for the info and instructions for this newb.


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## XtremeRevolution (Jan 19, 2012)

8141cruzer said:


> For what it's worth... I just bought my Cruze LT 1.4L last week (manufactured in June 2012). After reading the discussions and carefully following instructions given to remove and re-gap my plugs, I found them to all be at .025" which is within the GM spec of .6 - .7mm gap. My car has been running fine but I have a 6 sp manual trans so maybe that's keeping it from bogging down as some have noted. Many thanks for the info and instructions for this newb.


It's the guys driving with a 6 speed manual that have noticed the biggest difference when increasing spark plug gap, whether it's from .020" or from .025".


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## 8141cruzer (Jul 14, 2012)

Maybe my big fat size 13 right foot is keeping it from bogging down! My clutch life should be a cluehmy:. Great posts!


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## danimal (Oct 4, 2011)

We'll maybe I'll back it down to .028 this weekend, I've been running .035 and my "seat of the pants" dyno felt like it bogged less initially after the change. But its been so **** hot here with 100 and max AC in town not much helps. I think the temps are supposed to be the same next week so we shall see.

*i didnt realize the "d" word was an expletive :uhh:


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## XtremeRevolution (Jan 19, 2012)

danimal said:


> We'll maybe I'll back it down to .028 this weekend, I've been running .035 and my "seat of the pants" dyno felt like it bogged less initially after the change. But its been so **** hot here with 100 and max AC in town not much helps. I think the temps are supposed to be the same next week so we shall see.
> 
> *i didnt realize the "d" word was an expletive :uhh:


A/C will make your car bog down like crazy, especially if you have a manual transmission. If I have A/C on, I have to keep my revs up above 1900 to get any decent amount of acceleration.


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## coinneach (Apr 10, 2012)

XtremeRevolution said:


> A/C will make your car bog down like crazy, especially if you have a manual transmission. If I have A/C on, I have to keep my revs up above 1900 to get any decent amount of acceleration.


Agreed, but I'm not driving without A/C in 110F weather. I can put up with with the bog until October (when AZ generally cools back down).


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## Blue Angel (Feb 18, 2011)

Just checked the gaps on my '12 ECO MT, built in May, and all were between .025" and .030" (my gap gauge has wires at those two sizes for a go/no-go). If I had to guess I'd say they were all closer to .025" as there wasn't much freeplay with the gauge in the gap.

Has anyone seen a spark table for this engine yet? Hate to be blunt, but all the discussion about high intake air temps causing spark retard are kinda pointless unless you know for a fact the exact temperature that happens.

On a turbocharged engine there are two intake air temps that are important; the ambient air coming into the intake and the temperature of the air in the intake manifold, which will be higher or lower than ambient depending on the relative pressure and the efficiency of the intercooler when under boost.


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## XtremeRevolution (Jan 19, 2012)

Someone did post the spark table for IAT retard in another thread. It's significant. With IATs in the 100s, the PCM pulls 6+ degrees of timing, up to 10-12 if I remember correctly. That intercooler heat soaks pretty badly in traffic with the A/C on.

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## Chevyderek72 (May 16, 2011)

My plugs were at or just under .025, I re-gapped them to .035 and everything was great. I noticed rpm's coming up much quicker making my 1.4 MT much much easier to drive. After this official number came out I just re-gapped them down to .028 and again it is very sluggish, mainly when heat soaked. I forgot I re-gapped them and while driving today I realized my engine was terribly sluggish from a stop. But I remembered it was the plugs and had to get used to driving it like that. So I didn't notice much while not heat soaked, but definitely noticed it when it was.

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## unitednations161 (Mar 13, 2011)

so if we have them at .35 should they be regapped back down to .28?


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## obermd (Mar 3, 2012)

I'm leaving mine at 0.035". This was dead center in the original GM Service Manual for the 2012 Cruzen.


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## Aeroscout977 (Nov 25, 2010)

Stickied.


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## Chevyderek72 (May 16, 2011)

You don't have to drop it down, I just did with GM stating there could be adverse effects from making it larger than .028. I just like to sway toward the cautious side though.


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## unitednations161 (Mar 13, 2011)

Chevyderek72 said:


> You don't have to drop it down, I just did with GM stating there could be adverse effects from making it larger than .028. I just like to sway toward the cautious side though.


GM prolly thinks everyone who tunes the cruze is bad too :th_coolio:


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## Ranscapture (Jun 20, 2013)

So I'm confused. I need more power, my 1.8 is terrible in SF. But if I happen to run to a hot weather area, I don't want things to go bad as well. Should I stick to .028, or compromise and go to .030? .032? Any help please. I see on other threads your definitely stating .035 is the way to go. But here it seems .028 and that's where mine are at.


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## obermd (Mar 3, 2012)

Ranscapture said:


> So I'm confused. I need more power, my 1.8 is terrible in SF. But if I happen to run to a hot weather area, I don't want things to go bad as well. Should I stick to .028, or compromise and go to .030? .032? Any help please. I see on other threads your definitely stating .035 is the way to go. But here it seems .028 and that's where mine are at.


The 1.8 engine in the LS was always spec'd at .028" - leave them there. As for power, try premium gas. There is a noticeable difference between 87 and 91 octane in Penguin LS.


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## bobbykeene (Jul 5, 2013)

First time post - 2013 Cruze LTZ. Factory AC Delco plugs were all gapped to .025. Bought Autolite Iridiums and gapped to .034. Wow. Huge improvement with responsiveness and significantly reduces hesitation. Made my car way more fun to drive.


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## obermd (Mar 3, 2012)

When I regapped jxski07's plugs last week I set them to 0.030". He has a 2013 ECO MT and I didn't want to go higher since he doesn't have the tools to change the gaps. I was also concerned that GM may have done something to the ECU software for the 2013s that would make the 0.033 - 0.037" original 1.4T Cruze engine spec too big for the 2013s. His car is noticeably smoother and has more low end power. Original gaps were less than 0.025" and I also discovered that all four ignition coils were jammed in the sides of the boots. I unjammed the ignition coils while I was at it. The plugs were labeled AC Delco.


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## tlucas (Jan 11, 2014)

I just got the chance to check the gaps today on my new 2014 Cruze 1.4 and found that they measured .024" with feeler gauge. I changed them to .035" since this is what seems to be recommended. I haven't really noticed any driveability issues from an engine standpoint, but car is new and I'm still getting used to it. Acceleration is smooth, but tranny could be smoother. I have noticed one thing though. While on the interstate with cruise set at 65mph and going down a long hill, I feel a minor jerking, or a "cutting in and out" feeling. Wondering if this a normal feeling--maybe the engine cutting the fuel in a partial coasting situation, or trying to maintain speed on a downhill, I don't know. Not sure if this is the right place to ask this, or maybe I will start a new thread with the question. Thanks everyone. Can't even begin to say how much I'm learning on this forum. It's great!


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## obermd (Mar 3, 2012)

tlucas said:


> I just got the chance to check the gaps today on my new 2014 Cruze 1.4 and found that they measured .024" with feeler gauge. I changed them to .035" since this is what seems to be recommended. I haven't really noticed any driveability issues from an engine standpoint, but car is new and I'm still getting used to it. Acceleration is smooth, but tranny could be smoother. I have noticed one thing though. While on the interstate with cruise set at 65mph and going down a long hill, I feel a minor jerking, or a "cutting in and out" feeling. Wondering if this a normal feeling--maybe the engine cutting the fuel in a partial coasting situation, or trying to maintain speed on a downhill, I don't know. Not sure if this is the right place to ask this, or maybe I will start a new thread with the question. Thanks everyone. Can't even begin to say how much I'm learning on this forum. It's great!


The fact that all your plugs were consistent is a small miracle in itself.

The power surges you're feeling are DFCO engaging and disengaging and is completely normal. This can happen as often as once a second. If you pay attention these surges will alternate between power drop (you go forward in the seat) and power up (you go back in the seat). You can also see DFCO by switch your DIC to metric and watching the instantaneous MPG readout. When it drops to 0.0 L/100KM the car is in DFCO. In the automatics it takes about four seconds off the throttle to see the drop, two seconds in a manual. When running on cruze control it will happen much quicker as the computer is managing the entire throttle system.


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## tlucas (Jan 11, 2014)

At 65mph, I'm taching approx 2300 rpm's in 6th gear. So it is normal for DFCO to engage and disengage even at this rpm? I just didn't expect it to happen in this rpm range. I will check the DIC thing next time I'm out. Thanks for replying so quickly. Kinda thought it was normal. Just didn't expect to actually feel it.


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## obermd (Mar 3, 2012)

I've seen DFCO engage/disengage at 6,000 RPM. DFCO can engage anytime you let completely off the throttle and the engine speed is above 1500 RPM for two seconds (manual) or four seconds (automatic) and will disengage when the engine speed drops to 1250 RPM, you press the throttle, or press the clutch (manual). In the automatic DFCO is maintained through ECU managed downshifts. DFCO can also engage in any forward gear. I haven't tested in reverse but I don't see why it wouldn't work.


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## ZadeStorm (May 2, 2012)

I Gapped My Plugs to .35 back when this thread was first written.I have a 2011 Chevy Cruze with the 1.8L Motor.Today Is 1/23/14 and my car has 82000 miles on it and is now in the shop for a Check Engine Light.Chevy Dealer has concluded that the Ignition Coil And the Spark Plugs Need to be replaced.Now i'm not suggesting that this was because of the gap change but i was posting on here for people to be aware.I am by no means necessary a mechanic so please feel free to comment.Thanks


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## Blue Angel (Feb 18, 2011)

ZadeStorm said:


> I Gapped My Plugs to .35 back when this thread was first written.I have a 2011 Chevy Cruze with the 1.8L Motor.*Today Is 1/23/14 and my car has 82000 miles on it and is now in the shop for a Check Engine Light.Chevy Dealer has concluded that the Ignition Coil And the Spark Plugs Need to be replaced.*Now i'm not suggesting that this was because of the gap change but i was posting on here for people to be aware.I am by no means necessary a mechanic so please feel free to comment.Thanks


Did you by chance measure the gap of the plugs before taking it in for the CEL? Also, how many miles did you drive after your plugs were gapped (i.e. what was the mileage when you gapped them)?


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## ZadeStorm (May 2, 2012)

I had them regapped professionally at exactly 10,000 miles and no I did not have them checked before putting the car in the shop. I suppose that would have been worth looking into thanks.


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## prince_bigd (Jul 16, 2013)

if you started with a gap of 0.035 even with iridium plugs after 72k miles youve seen some significant gap growth. Im going to hazard a guess that your gaps were probably over 0.040 or greater after that long. If so then its entirely possible the only true issue was the gap which could have been solved with just new plugs. If you were running copper plugs then they were probably completely shot after that length of time.


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## Blue Angel (Feb 18, 2011)

Plug gap growth is definitely a concern after that long. Not to discredit the tech who gapped your plugs, but there's also a chance they were set wide unless you verified them after they were set... if you say .035", they may think .035" +/- .005 is good enough. Setting plugs consistently takes patience.

Possibilities:

1. Misfire. With an excessive gap there's a chance the spark found something easier to jump to than the ground electrode. Once a misfire happens a carbon trail forms and it happens more and more frequently.

2. Coil pack failure. There are some complex physics involved in the collapsing of the coil voltage that change dramatically with a change in plug gap. It's possible if the gaps were crazy big the coils may have failed due to increased stress. I can't remember the details off the top of my head, and I'm on my cell phone typing microscopic text (not the app)... searching is a pita.


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## billbo (Oct 9, 2012)

Hey guys,

I've never gapped/cleaned or replaced my spark plugs. I'm sitting at 80 000 km. Am I due for an upgrade?


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## obermd (Mar 3, 2012)

billbo said:


> Hey guys,
> 
> I've never gapped/cleaned or replaced my spark plugs. I'm sitting at 80 000 km. Am I due for an upgrade?


I'd check the gaps but they should be good for another 20,000 km.


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## cumminsdieselfreak (Jan 26, 2015)

Has anyone switched to the NGK laser iridiums from the AC Delco Iridiums? If so, what was the overall performance difference?


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## jblackburn (Apr 14, 2012)

cumminsdieselfreak said:


> Has anyone switched to the NGK laser iridiums from the AC Delco Iridiums? If so, what was the overall performance difference?


They are one and the same. NGK makes the AC Delco IFR series plugs in the car. 

Give the BKR iridium series a try. (BKR7EIX - stock heat range or BKR8EIX) Lots of people have good experience with them.


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## cumminsdieselfreak (Jan 26, 2015)

10-4


Sent from AutoGuide.com Free App


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## road_dog (Dec 21, 2015)

i bought brand new Iridium spark plugs Acdelco part#41-121 and according to the Orielly website and the hot white chick at the counter said these plugs i pruchased are at the .027 inches (.7 mm) gap after reading previous threads and including this one then this should be good to go i dont have a feeler gauge to check them should i take thier word that they are properly gapped... thanks in advance




XtremeRevolution said:


> As promised, here is the official statement from GM. Tom Read (GM Powertrain Communications) has run this by both GM Service Engineering-the guys who engineer fixes for issues (Detroit), and GM Product Engineering-the guys who designed the motor (Germany for approval. This is about as official as it gets.


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## obermd (Mar 3, 2012)

road_dog said:


> i bought brand new Iridium spark plugs Acdelco part#41-121 and according to the Orielly website and the hot white chick at the counter said these plugs i pruchased are at the .027 inches (.7 mm) gap after reading previous threads and including this one then this should be good to go i dont have a feeler gauge to check them should i take thier word that they are properly gapped... thanks in advance


No. If one of the plugs was dropped it can be under-gapped. Get a set of feeler gauges - they're cheap - and verify the gap yourself.


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## zen_ (Mar 15, 2015)

road_dog said:


> i bought brand new Iridium spark plugs Acdelco part#41-121 and according to the Orielly website and the hot white chick at the counter said these plugs i pruchased are at the .027 inches (.7 mm) gap after reading previous threads and including this one then this should be good to go i dont have a feeler gauge to check them should i take thier word that they are properly gapped... thanks in advance


The set I bought was gapped precisely to those specs, but like obermd said, it's possible that between manufacture and install, that could change since auto parts can get shuffled around many times before they are placed in your hand. 

If you have any inclination whatsoever to mess around with spark plugs, get one of the wire type gauges like the KD 165 that has a 0.028" wire (GM spec) and 0.032" wire (max recommended). It cost all of $6, and is a superior tool for checking the gap on a worn ground electrode. For whatever reason, the 1.4T is ridiculously sensitive to the spark plug gap. Having it set precisely correct, and being able to check it if something feels amiss is very much worth the time and effort.


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## Tmiller39 (Oct 18, 2016)

I just purchased the Bkr8elx they came gapped at like .22 should I regapp them to .28 or what looking through all these posts I can't decipher what to go with


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## nds76 (Aug 14, 2016)

What brand plugs would you recommend for my 2012 Cruze 1.4L Turbo? Is AC Delco the way to go? Is the proper gap 0.6 - 0.7mm?


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## 2015LT2 (Jan 20, 2017)

I guess this would bring _closure_ to the subject of spark plug gaps (pun).:tongue:


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## benissimo (Sep 17, 2018)

Speaking of inconsistency.
I went to get new plugs for 1.4L. Just to get the stock delco 41-121. Says gap is .028. I looked at them with the gap checker at the counter- I know this 1 dollar thing is probably not the gold standard of measurement, but all 4 were different, ranging from .020 to almost .050. Wondering if I have ever had correctly gapped plugs before. Also, isn't it generally discouraged to mess with the gaps on these fine wire plugs?


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## intrigued214 (Sep 8, 2018)

I gapped mine. Used feeler gauges and gently pried on ground strap with pliers as necessary. If they needed to be closed I tapped them gently on a piece of wood


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## power4utoo (Dec 11, 2018)

OnlyTaurus said:


> Nicely done, Andrei! GM Service Information has been updated thanks to you.
> 
> Ignition System Specifications
> ApplicationSpecification MetricEnglish Ignition TypeCoil-On-Plug Firing Order1–3–4–2 Spark Plug TypeRefer to Electronic Parts Catalogue Spark Plug Torque25 N·m18 lb ftSpark Plug Gap0.7 mm0.028 in
> ...


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## Thebigzeus (Dec 2, 2018)

So what is the recommended "tuned" gap? Smaller or larger or the same?


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## jblackburn (Apr 14, 2012)

Thebigzeus said:


> So what is the recommended "tuned" gap? Smaller or larger or the same?


0.024-5" or thereabouts.


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## Jarret (Feb 4, 2021)

The Butcher said:


> Just re-gapped last night to .028 after reading this and I actually think the car is doing the best it's done so far! Initially they were .019 - .022 and I re-gapped to .035 about two months ago. I think the larger gap and all this AZ heat was causing spark blowout at higher RPM's,cause the car felt like it would nose over around 4,000 rpms, now it seems more consistent under heavy acceleration... Thank you for putting in the time with GM to get clarification on this issue!!
> 
> 
> Sent from my Autoguide iPhone app


I agree with that, I tapped to .035 and it had great off the line but above 3800 it would just kind of lose everything it had, so you recommended .028?


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## Blasirl (Mar 31, 2015)

Jarret said:


> I agree with that, I tapped to .035 and it had great off the line but above 3800 it would just kind of lose everything it had, so you recommended .028?


Untuned - .028
Tuned - .024


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