Issue while changing spark plugs

I did my 120,000 mile spark plug change yesterday with OEM Denso K20HR-U11 plugs. After finishing up, I took the truck on a test drive. After driving less than a mile, the truck started running rough (RPM’s surging, misfiring) and the check engine light started flashing.

I limped it home and pulled the codes.
P0300 random misfire
P0303 3rd cylinder misfire
P0304 4th cylinder misfire

I pulled all the plugs and rechecked spark plug gaps (all within spec) and reinstalled them, then started the truck again. It was immediately running rough and threw a check engine light after about a minute.

I then pulled the 3rd and 4th plugs and replaced them with 2 of the old plugs I had just taken out. The truck now runs perfectly.

Is this as simple as getting 2 bad brand new plugs? Or is there something I am missing?

 

Try new plugs. The new ones may have been dropped and cracked.

Other possibility is you got some fake ones. There's lots of fake OEM spark plugs floating around Ebay and even Amazon. I get mine from the dealership and for whatever reason they are cheaper than I can buy in the store or online.

If the old plugs work, it is a problem with the new ones.

 

If changing the plugs solved the problem, more than likely it was bad plugs.

There is a small chance you didn’t get the coil snapped on the plug good. Or the actual coil pack connector plugs on good. But they aren’t really know to be difficult to connect.

I’ve heard the 4.0 is easy to break the porcelain on the plug if you tighten them too much. But I’m about 90% sure I got mine over torqued. And nothing happened yet. I have never used a torque wrench on plugs.

 

Thanks. That's what I assumed, just wanted to make sure I wasn't missing something else. I did get the plugs from Ebay, but they were from a highly rated seller that I have used before with no issue.

I don't think it was bad connections, because I changed the plugs twice and checked all the connections really well.

 

I picked up a set on Amazon and they turned out to be fakes. Denso posted some resources to help identify.

https://www.denso-technic.com/fighting-the-fakes

 

Sadly, Amazon hasn't been great about counterfeit items in some product categories that are critical on quality.

 

@irayfz6 For giggles you should show us a pic of the box and a plug. Let's see if you got burned by fake Ebay plugs.

 

Hi Joey

Can't do much other than try again with a new set of plugs

 

I’m not criticizing you bud.

But spark plugs are relatively cheap to begin with. Anytime you find them “cheap”.
You have to ask yourself, “Where is the profit at?”

I still go to my local auto parts store or even the dealer for somethings.

 

Totally agree. Still amazes me why more folks don't use parts.toyota.com to order through. A lot of the (local) dealers that sell on there offer a hefty discount off MSRP.

 

This exactly. Especially when considering Toyota offers free shipping on all orders over $75(?) with the "freeship" coupon code. Just shop around and find a dealership near you that comes close to matching toyotapartsdeal.com, use the free shipping code and boom, you saved a bunch of cash.

 

My first Amazon plugs looked to me like they were counterfeit. Some of the U grooves were badly off center. I ran them for quite a long time, engine ran fine, swapped them out early.

It's an easy mistake to do, so don't be insulted if you know better. Is it possible you missed getting the plug into the coil?

 

Unfortunately I already threw the boxes away, and today was trash day so they’re long gone. But here’s a pic of two bad plugs. One is definitely cracked

 

Howdy Alex

 

It’s not the cost savings if there even are any. Just availability. I don’t live near a Toyota dealer, so eBay is easy

 

Hard to tell. They look legit. I'd say you have 2 cracked ones. Other one just isn't visibly obvious. Get 2 more and call it good.

 

I just avoid sparkplugs from ebay or Amazon and get them from rockauto. Never had a problem with denso plugs from them.

 

Well speaking of counterfeit toyota parts :
https://youtu.be/FVA4RYql9KU

 

Why would anyone go the trouble of of counterfeiting spark plugs that only cost a few bucks to begin with?

 

These are cheap enough that I would just go to the dealer and redo them and go from there