Spark plug gap set wrong from the factory - MPG & misfires?

[Fastlerner]

Saw this mentioned in another thread here (it also has a dedicated thread over on Hyundai forum), but it's important enough that it deserves its own space here.

Apparently many of our cars are coming with incorrectly gapped plugs from the factory. The stock plug is a Denso ZX20hCR8. These are new plugs and are not available retail yet, but can be bought through the dealer for about $20 each.

Denso recommends a gap of 0.8 mm or 0.032 inches for the plug, however HMAservice shows a gap of 1.0 ~ 1.1 mm (0.0394 ~ 0.0433 in.) for our engine.

I checked all of mine and they were gapped between .026 and .028!! I regapped all of mine to .032 and after a quick test drive there did seem to be some improvement. I'll probably run on it for a week or so to be sure, then I'll try regapping to .040 or so.

Frankly I'm amazed at how widespread this short-gap issue appears to be considering they're coming this way straight from the factory. If you're one of the folks scratching your head as to why you seem to be getting sub-par mileage, or rough starts and random misfires, I would check this immediately.

Oh, you'll need a 5/8 plug wrench and a 10mm to remove the coils. Tightening torque is 3.9 ~ 5.9N.m (0.4 ~ 0.6kgf.m, 2.9 ~ 4.3lb-ft). And be careful with those electrodes! At only only .04 wide the iridium electrode is very thin.

[bmw7891]

Hmmm. Changing my oil today, so ill have to check mine while I'm at it

[LTR]

How hard is it to get the plugs on our engine?

[Fastlerner]

To get the plugs? Or to get TO the plugs?

You can get replacements at the dealership.

As far as getting to them, its VERY easy. Just open the hood and pop the cover off the engine. (It's secured in 4 spots and just pops loose when you lift straight up.)

From there the coils are right on top of the engine and each is secured with a single 10mm bolt. Pull the coil/boots out and a standard 5/8 sparkplug socket pulls the plugs right out. Reassemble in reverse.

As I said, be careful with the plugs as the iridium electrode is very thin.

[LTR]

Perfect thank you. I admit I've never popped that plastic cover off. Glad to here there easy to get to though.

[2.0T/Vic]

So any news on what gap is better for the engine ?

[Gixer1k]

After seeing this I regapped mine to 1.0mm. I commute 52 miles a day, so I'll provide an update in a couple days.

[Fastlerner]

I've been running all week with mine gapped at .032 and WHAT A DIFFERENCE! I've definitely been more heavy-footed than normal to get a feel for the change in power and even so, my mileage is the same as when I was babying it.

Now that I know how she drives at that gap, I plan on moving it to .040 this weekend for another test week. Updates to come.

[bmw7891]

Mine was all at .026 to .028 as well. I changed mine to .035. Let's see how it does when I go to work later.

[bmw7891]

I took a pic of the plug. Appeared to be carbon deposits on it. Is that normal for a DI engine?

[doeboy]

I need to buy me a feeler guage so that I can verify my gap. Man changing out these plugs looks very simple. On my last car I had to undo hoses, intake tube, and some other things which took some time to do it. It was a PITA. This looks like it could be done within a half an hour from start to finish if not sooner

[bmw7891]

Piece of cake. Took me about 15 min maybe.

[Fastlerner]

I took a pic of the plug. Appeared to be carbon deposits on it. Is that normal for a DI engine?

I saw that on a couple of mine too. I'm guessing it was due to wrong spark-gap resulting in an incomplete burn. Time will tell.

[bmw7891]

That's what I was thinking. Maybe less soot on the tailpipes now too lol

[Robfrmny21]

Cars are tuned a lil rich to protect the motor.