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What Was Your Spark Plug Gap?

136829 Views 474 Replies 193 Participants Last post by  snowwy66
If you changed your spark plug gap per this thread or this thread, please report what the original values were here. If you have yet to change them, please remember to report the original values.

My case with GM has been escalated to a district case manager at GM to hopefully get some exposure on this issue. My primary goal is to allow people to go to their dealerships and have their spark plug gaps checked and corrected (as there has been a 100% error rate so far), and the more people and numbers I can present them with, the better.

If your username is on the below list, I already have your numbers down. If not, please post them. I need specific values, such as ".022, .023, .025, .025." I will also need the model year of your Cruze.

We have 37 cars recorded so far. I'd like to get at least 50. My current spreadsheet is also attached.

InsaneSpeed Steve
Red Dragon
Higgs Boson


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Good suggestion.

If those who have already reported their numbers would provide the year of their vehicle, I can certainly have that added to the spreadsheet. I will add those values for all newly reported gaps.
It would be nice to know if the engines are 1.8 or 1.4T as well. This may give us an idea about the severity of the problem for each engine.
2012 ECO MT, final assembly Oct 2011

0.023, 0.025, 0.025, 0.023

All now at 0.035 - 0.036
For those of you who work better visually, I graphed Xtreme's sheet after adding albow77. There is a very definite peak at 0.025 with the plug gap margin of error being -0.002 +0.001.

Line Text Plot Diagram Slope
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That visual graph sure makes it look like NGK thought they were supposed to be .025, and there were serious quality control problems on top of that.
Agreed. There are now enough plugs (> 100) in the chart to start doing statistical analysis, but I think just seeing it graphically is sufficient. It also appears NGK was given the same spec for both the 1.4T and 1.8 engines, which makes me wonder if they shouldn't both be 0.035 +- 0.002, despite what both the owners manual and the GM service manuals say.
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Checked today, 5/28/12:
2012 Cruze Eco 1.4, AT, 5800 miles: .028, .026, .028, .028. Only adjusted the .026 to .028. Now all in line with specs per the manual.
I would go with the 0.035" what's in the GM maintainence manual. It's more current than the owners manual.
For the two of you who reported the really small gaps, what are the last 6 digits of your VINs (if you don't mind)? I wonder if a shipment of spark plugs got banged up or dropped on the way to your cars.
Just did mine today. All four were at .025. I re-gaped to .031. Should I go to .035?

2012 cruze ls
The US spec is currently 0.028" - I saw this myself in the on-line service manual at my dealership. According to AC Delco Australia the overseas spec, converted to inches is 0.0315.
0.016 would explain why you were having such a hard time shifting smoothly.
Thanks. I think the chart just about says it all.
I can run 87 octane again - even in the heat of summer. Before I regapped I had to run 91. Yeah!!!

It sounds like you ran into the same problem that occurs in the US a lot - crappy dealerships. The service manager at the second dealership seems to know what he's doing.
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I just finished doing my spark plugs. All 4 were gapped at .025. I have regapped them all to .035. My car was built 3 weeks ago.
So either GM has done nothing or there are still misgapped plugs in the supply line. My bets are on both.
this point i doubt gm knows enough about it yet. Your best bet is to just gap them your slef and make sure your dealership knows about it. I printed this forum out and brought it to my dealership and they offered to regap them for free. I had already done it so it doesnt matter. The dealership let me know the process on how these things work and how slow the message would get to GM. R&D made sure the cars run, which they do. NGK has alot of the balme in my mind, in fact i messaged them and havent heard anything back yet.
NGK would only have blame for the inconsistency in gaps. It really appears GM gave the wrong spec to NGK. As for GM, they know about it. That's one of the reasons GM set up their Social Media unit - to let GM corporate know when owners of GM products find problems with their cars. Note to Stacy - this isn't a ding on your being here, just an observation on the mission of GM's Social Media unit. Whether or not GM will do anything unless the media gets involved is a different question entirely.
GM has probably closed ranks and notified their powertrain folks to not say anything by this time. I can see the variance being somewhat subjective, but the peak at 0.025 isn't. I know my two plugs that I reported at 0.023 were an estimate based on the wire gapper I have just barely not slipping through at 0.025. The 0.025 loop just slipped through the other two tools, touching the wire but not blocking it.
Just checked mine (2012 1LT).

.025-.026 across the board.

Regapped to .028

A lot of us have regapped to the 0.035 listed in the service manual. Please let us know how your car responds to regapping to 0.028".
I'm liking this Tom Read guy. He seems to prefer to respond to me via phone instead of email, and promptly at that.

He spoke to two service engineers who owned Chevy Cruzes, and they went out and checked the gap on their cars, then came back. One of them gave him exact specs, and said that they were at .025". Basically, GM now knows there's a big issue when their own engineers can confirm it with their own cars. He told me they have a lot of people working on this issue right now, investigating the assembly line as well as dealing with vendors to determine where the problem is. He mentioned a conference call he had in a few minutes regarding this very issue, so safe to say, my conversations with him have definitely created a great deal of exposure.

Thanks again to everyone who took the time to measure and report their spark plug gaps back. The spreadsheet I was able to put together with that information really helped push for an investigation. Now that the issue is confirmed internally, this should get interesting.

I also reminded him about the automatic transmission spec, and he said he'll ask about that as well in his next meeting.
Are you going to add "GM Engineer" 0.025 x 4 to your spreadsheet? Just a thought. I suspect and hope Mr. Read has pulled up CT and read through, and possibly printed, the threads concerning spark plug gap.

Good news! It's nice when you actually find someone in the chain of bureaucracy that can actually accomplish something, isn't it?

Reminds me of having to deal with Verizon at times...trying to get someone that actually knows what they're doing on the other end of the phone.

I'd be interested to know what they determine the preset gap is supposed to be, but I definitely won't be changing my plugs back. It runs swimmingly well on .035", so much so that I have gotten used to shifting under 2000 RPM most of the time around town and can be in 5th or 6th gear at 35 mph.

Before I was driving it like I thought was normal for a 1.4 liter 4-cylinder (and most other small 4-cylinders I've driven without a turbo) - at 3000 RPM or above. I still do when I need to keep up with faster traffic, but I feel like I have to push the car much less now, even with the AC running.
100% agree unless GM Powertrain can provide an engineering answer as to why the North American 1.4T Cruzen should be at 0.028 while the Holden 1.4T Cruzen are at 0.035.
Large company => lots of stakeholders. Making changes in any large company takes time. Xtreme, thanks for your efforts on this.
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@Xtreme: I've re-gapped the spark plugs to 0.038" (my stock is 0.044"). For the low speed, it is better than stock gap, but for middle and high speed, it lacks power in comparison with stock gap, so that I turn back to stock gap. I found in Google that, more wider gap (in limitation) will have more electric.

I think that before regapping the gap, it is necessary to consider which type of spark plug, because some car use different type of spark plugs. If default gap is more than 0.038", there is no need to regap spark plugs, but if default gap is below 0.03", it is better to regap spark plugs. My car uses NGK ZFR6U-11, and I think that 1.4L will use another type.
Do you by any chance have the all wheel drive Holden Cruze? That was the only cruze to use 1.1mm spark plug gaps.
has anyone read this thread from Vince at trifecta?

So... What exactly is the spark plug gap supposed to be on the 1.4 turbo?? - 1.4L Turbo (LUJ, LUV) and 1.6L Turbo (LLU) -

what are your guy's thoughts? i want to check to make sure my gaps are correct on my new car but it seems like it should be .028 not .035.
In a nutshell, if you have a tune, gap to 0.028". Otherwise the current GM Service manual says 0.035" +/- 0.05mm. GM is working on this issue and may come back and say 0.028" for all North American Cruzen, however.
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