[XtremeRevolution]

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.

The 2012 North American Cruze Service Manual spark plug gap information was incorrectly listed as 0.85 - 0.95 mm. A change is being implemented to correct that information to 0.6 - 0.7 mm. This information is in the process of being updated in dealers online service information. A service bulletin will not be issued. The spark plug gap for the Cruze 1.8L engine is the same: 0.6 - 0.7 mm.

The 2012 and 2013 North American Cruze Owner’s Manual spark plug gap will remain unchanged at 0.7 mm as they are already printed. The gap is the same for all North American model Chevrolet Cruze models with the 1.4L and 1.8L engines regardless of model year.

We are investigating changing future Owner’s Manual information to state the range, vs. just 0.7 mm which is the high limit, to be consistent with the Service Manual.

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.

I hope this resolves your questions. Thanks to you and all of the Cruze owners for bringing the plug gap discrepancy to our attention.

Best regards,

Tom Read
GM Technology Communications, Powertrain

 

[XtremeRevolution]

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.

 

[Bohdan]

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.

 

[XtremeRevolution]

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.

 

[obermd]

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.

 

[deerebilt]

Thanks for your work xtremerevolution

 

[boats4life]

Gentleman and a scholar, this one. lol

Good work, Andrei.

 

[OnlyTaurus]

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.

 

[The Wolf Wagon]

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

 

[The Butcher]

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]

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.

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.

 

[rbtec]

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.

 

[XtremeRevolution]

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.

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.

 

[rbtec]

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.

 

[Beaker]

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

 

[NYCruze2012]

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]

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

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[hawkeye]

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.

 

[Blue Angel]

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]

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.