Are Your Spark Plugs Gapped Incorrectly?

152671 Views 545 Replies 129 Participants Last post by wasney, Jun 2, 2015

XtremeRevolution

Discussion Starter · May 9, 2012

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:

http://www.cruzetalk.com/forum/27-fuel-economy/6468-spark-plug-gap-fe-1-4t.html

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.

Reactions: 5

21 - 40 of 546 Posts

Vetterin

· #21 · May 10, 2012

coinneach said:
It's the 5/8" spark plug socket and T-40 torx bit.

Actually it's a T-27 torx (same size that you use for your rear brake drum screw removal).
Anyway, I just pulled my plugs 10 minutes ago and sure enough, 3 were @ .024 and 1 @ .025. I regapped to .034 and can't wait for my drive to work tomorrow. The entire job took 15 minutes. Man do I love working on this engine. For those that are going to check theirs DO make sure you check the springs inside the spark plug boot as I found 2 that were kinked to the side and I don't think it was caused by me but installed that way.

sciphi

· #22 · May 10, 2012

Vetterin said:
Actually it's a T-27 torx (same size that you use for your rear brake drum screw removal).
Anyway, I just pulled my plugs 10 minutes ago and sure enough, 3 were @ .024 and 1 @ .025. I regapped to .034 and can't wait for my drive to work tomorrow. The entire job took 15 minutes. Man do I love working on this engine. For those that are going to check theirs DO make sure you check the springs inside the spark plug boot as I found 2 that were kinked to the side and I don't think it was caused by me but installed that way.

You sure you didn't do my engine? That's exactly what I found on mine. I regapped to a hair over 0.030". Good use for a traditional feeler gauge, and practice for the upcoming valve adjustment on our Honda.

XtremeRevolution

Discussion Starter · #23 · May 10, 2012

sciphi said:
You sure you didn't do my engine? That's exactly what I found on mine. I regapped to a hair over 0.030". Good use for a traditional feeler gauge, and practice for the upcoming valve adjustment on our Honda.

Sounds like you should up those a bit to .035.

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evo77

· #24 · May 10, 2012

AkotaHsky said:
The cost of the tool is my question. Thats the tool linked above? Or just a coin gapper? It looks like itd be more than $3.

Sent from my PC36100 using AutoGuide.Com Free App

http://www.autozone.com/autozone/ac...ByKeyWord=spark+plug+gapper&fromString=search

Reactions: 1

UR2NOZ

· #25 · May 10, 2012

Did this to mine yesterday. 1.4L Looks like all were right about .25-.26. I took them all up to .35. So far I wasn't in shock and awe after the adjustment but I didn't expect to be either. Car runs smooth fuel mileage seems the same based on my normal 80miles round trip to work each day.

XtremeRevolution

Discussion Starter · #26 · May 10, 2012

UR2NOZ said:
Did this to mine yesterday. 1.4L Looks like all were right about .25-.26. I took them all up to .35. So far I wasn't in shock and awe after the adjustment but I didn't expect to be either. Car runs smooth fuel mileage seems the same based on my normal 80miles round trip to work each day.

Wait till you fill up at the pump after the tank is through. I'd expect a 1-2mpg boost.

bubby2411

· #27 · May 10, 2012

going to check mine to see what they are, if they are at the .2 range i will be going to buy ngk spark plugs and putting new ones in my car! hopefully i can check it this weekend

XtremeRevolution

Discussion Starter · #28 · May 10, 2012

bubby2411 said:
going to check mine to see what they are, if they are at the .2 range i will be going to buy ngk spark plugs and putting new ones in my car! hopefully i can check it this weekend

No need for NGK spark plugs. The ones in the Cruze are excellent and are Iridium plugs as well. You'd see zero gains going with an NGK plug over what's in there already, but you'd see a hole in your wallet instead.

crzyfirefighter

· #29 · May 10, 2012

ok just got doing this to my cruze with the 1.4l turbo... man glade i did... one was gaped at not even .19 and the others not even close to .25... gaped them all at about .36... went and fuelled up.. will report back later in the week what my mpg are.. i've been getting about 25 to 27 mpg on a full tank....again glad i did this.. thanks for the heads up

Reactions: 1

XtremeRevolution

Discussion Starter · #30 · May 10, 2012

crzyfirefighter said:
ok just got doing this to my cruze with the 1.4l turbo... man glade i did... one was gaped at not even .19 and the others not even close to .25... gaped them all at about .36... went and fuelled up.. will report back later in the week what my mpg are.. i've been getting about 25 to 27 mpg on a full tank....again glad i did this.. thanks for the heads up

.19!!! Wow. It's disturbing to find that these are gapped so far off what they should be, and so inconsistently at that!

Did you notice any difference in how the car drove?

UR2NOZ

· #31 · May 10, 2012

XtremeRevolution said:
No need for NGK spark plugs. The ones in the Cruze are excellent and are Iridium plugs as well. You'd see zero gains going with an NGK plug over what's in there already, but you'd see a hole in your wallet instead.

Wait....mine has factory NGK plugs installed. Do they not all come with NGK anyhow? I am confused.

Reactions: 1

XtremeRevolution

Discussion Starter · #32 · May 10, 2012

UR2NOZ said:
Wait....mine has factory NGK plugs installed. Do they not all come with NGK anyhow? I am confused.

Are they NGKs from the factory? I never bothered to actually check what brand they were. If they are, even better!

UR2NOZ

· #33 · May 10, 2012

XtremeRevolution said:
Are they NGKs from the factory? I never bothered to actually check what brand they were. If they are, even better!

Yes Sir, says right on the plugs. I to was surprised.

Reactions: 1

crzyfirefighter

· #34 · May 10, 2012

XtremeRevolution said:
.19!!! Wow. It's disturbing to find that these are gapped so far off what they should be, and so inconsistently at that!

Did you notice any difference in how the car drove?

seemed a bit peppier.. didn't really have to drive to far for gas.. so i will pay attention tomorrow on the way to work.. and yes it was quite a difference in the gap... plus all the springs were wedged off to the side...

OnlyTaurus

· #35 · May 10, 2012

Here.. if you guys did not know.

GM's specified gaps(directly from SI):

1.4L - 0.0335–0.0374 in
1.8L - 0.028 in

Reactions: 2

XtremeRevolution

Discussion Starter · #36 · May 10, 2012

OnlyTaurus said:
Here.. if you guys did not know.

GM's specified gaps(directly from SI):

1.4L - 0.0335–0.0374 in
1.8L - 0.028 in

Yep, we've confirmed this. Thanks for confirming it again (being honest, no sarcasm). What confuses me is why they recommended such a small gap for the N/A motor and a larger gap for the Turbo motor, lol. Coineeach seems to be loving his .035 gap on his LS though.

UR2NOZ

· #37 · May 10, 2012

crzyfirefighter said:
seemed a bit peppier.. didn't really have to drive to far for gas.. so i will pay attention tomorrow on the way to work.. and yes it was quite a difference in the gap... plus all the springs were wedged off to the side...

Springs were not wedged originally. When you unseated the coils from the plugs they do that FYI.

Reactions: 1

OnlyTaurus

· #38 · May 10, 2012

XtremeRevolution said:
Yep, we've confirmed this. Thanks for confirming it again (being honest, no sarcasm). What confuses me is why they recommended such a small gap for the N/A motor and a larger gap for the Turbo motor, lol. Coineeach seems to be loving his .035 gap on his LS though.

I would assume the larger gap for more volume and dense air from turbo. Smaller for just atmospheric pressure. Like you said preivously, larger gap ensures all the mixture is burned.

crzyfirefighter

· #39 · May 10, 2012

UR2NOZ said:
Springs were not wedged originally. When you unseated the coils from the plugs they do that FYI.

my bad.. first time doing anything with this car... only had it for about 3 weeks now

XtremeRevolution

Discussion Starter · #40 · May 10, 2012

OnlyTaurus said:
I would assume the larger gap for more volume and dense air from turbo. Smaller for just atmospheric pressure. Like you said preivously, larger gap ensures all the mixture is burned.

Right, it's just that historically, they've used smaller gaps on forced induction motors to prevent spark blowout. The spark plug gap for my N/A 95 Regal was .060 to give people a comparison.

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