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Are Your Spark Plugs Gapped Incorrectly?

152827 Views 545 Replies 129 Participants Last post by  wasney
I'm creating this thread to increase exposure of what appears to be a very common issue (affecting 100% of Cruzes so far). This stemmed from the following thread:

My original experiment was to increase spark plug gap over what they are gapped from the factory and test for measurable gains in fuel economy. What I didn't realize was that I had actually gapped them to the correct spec, and they were gapped much too small from the factory.

AllData specifies a spark plug gap of .033-.037 for the 1.4L Turbo motor. Reports so far have come back with .024, .025, .026, and .029 as measured spark plug gaps from the factory iridium plugs. These should have been pre-gapped from the distributor, but clearly weren't.

Coinneach checked his spark plug gap on his Cruze LS with the 1.8L N/A motor and found a .020 spark plug gap, which is absurd for a N/A motor and is smaller than he or I have ever seen before in any engine. He increased that to .035 and had the following to say when I asked if he noticed a difference:

Like a whole new beast. It's not quite as zippy as the 1.4T in the Eco that I drove when I was shopping, but it's a *censored* of a lot snappier now.

I currently don't know what AllData specifies for the Cruze LS, but if someone can get that information into this thread, it would be of great benefit to everyone. Hopefully, someone will get a tutorial/video made soon. There are significant performance and fuel economy gains to be had by correcting the spark plug gaps on these cars.
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I checked my gap on my 2013 Cruze LTZ, 1.4L Turbo. 3 our of 4 plugs were just under .025", one was just over .025". I re-gaped them all to .036.

I can't say as I see any huge differences in the way the car runs. It might possibly have a little less lag from a dead stop, and maybe gets slightly better gas millage ( certainly not any worse ). If I am seeing any real difference in MPG, it's probably 2% or so. ( went from 35.4 to 36.1 MPG in my daily driving, which is about 70% high way (70MPH ) , 25% two lane blacktop rural hwy (45 to 55 MPH), 5% small city driving (very few jack rabbit starts or stops) ).

For GM to 'fix' the problem of the GAP not being right, I suspect they'd have to get the spark plug maker to 'fix' the problem. I highly doubt that anyone at GM is going to be re-gaping mass quantities of plugs. Also, the 2013 Cruze owners manual still lists .028" gap for all engines. Meanwhile the average person owning a cruze would likely never notice a difference between having their plugs at .025" vs .035".
Take a look at my first post in I did some computations on my OEM plugs when I pulled them and figured out why GM came back with 0.025-0.028" for the plug gap when installing them.
When I checked mine earlier when this thread started pumping my 13 eco m/t all read .028" .... all 8 of them

just kidding all 4
The owners manual calls for 0.028 gap for both 1.4L & 1.8L.
The owners manual calls for 0.028 gap for both 1.4L & 1.8L.
For the 2013 and later model years, and the footnote states this is for replacement plugs only. For 2011-2013 the 1.4T was listed at 0.033 to 0.037 inch. This is also what was in GM Global Connect.
Just read all 55 pages of this. My car has 118k miles. Guess I will set my new plugs at .035. Never expected to read so much on the subject of plug gap.
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lol yea I have read through this before too. If you buy copper replacements then gap them at .28. I recommend them, they seem to make the car drive better.
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