3.4 spark plugs?

I did a valve cover repair and spark plug change yesterday. First time I've ever changed them. What I found was dual denso plugs in the drivers side with single NGK on passenger side. Is this normal?? The plugs were extremely worn.

 

Yes, that's how they came from the factory. Mine were like that as well when I just changed them at 180k.

EDIT: I'm sorry, both are dual electrode.

 

Yes it's normal for all Tacomas from the factory.

 

Yup. When I changed mine I went dual Denso in all 6.

 

I just put in OEM NGK NICKEL SPARK PLUGS (

$6 BKR5EKB-11 NGK Spark Plug Stock # 3967

BKR5EKB-11) (6)

 

38k on NGK

Denso went back in

233k on 4Runner 3.4

 

I went by the manual...not to mention, mine had 5 Autolite plugs mixed with one Bosch plug plus Pep Boys plug wires. Went with NGK (TE66) wires too

 

can’t remember why they did that. Someone on a thread awhile back explained why it was Densos on one side and NGK on the other.

 

Yea I had heard Denso and NGK mix before but never single and dual mixed. I meant to take pictures but forgot...

 

I think it might be because different sides of the engine were manufactured in different locations.

 

Dual electrode Denso and NGK from factory yes, single electrode no.
The "most" likely reason for the factory mix is a business practice known as "Vendor Management" and the fact that Toyota owns a huge chunk of both Denso and NGK. There are no performance, operational or assembly theories that hold any water.

There are a couple things to note on "reading" these plugs. The NGKs from the factory and even some from aftermarket sources came "pre gapped" wrong. For a time NGK even listed the gap wrong, much smaller than the Toyota spec that the Densos came properly set with. IIRC it (NGK) was something like .023" with Toyota spec at .043".
In addition one side of the 3.4 fires center to ground while the other side fires ground to center. This can contribute to the perceived erosion and promote a bit of false "brand loyalty".
Below are the factory plugs form my truck at 30K. The Densos show a larger gap and much more erosion on the center electrode.

 

I just purchased a 2003 and plan on changing the plugs which ones do I choose? Seems like they have to be dual electrode? I was considering the new Denso long life iridium IK16TT long life but I'm pretty sure they're single electrode even though Denso claims they're fine. Do I buy all 6 of the same?

 

Standard copper generally perform best, yes they have to be changed more often but IMO from my 03 it ran best with standard copper over the higher end plug. Yes all y will be the same. All Tacomas come half Denso/NGK but you can get the Denso at dealership cheap.

 

I got my new Denso plugs from Toyota. They were like 2-3$ a piece

 

As the engine is moving down the assembly line, there are workers on both sides with tasks to do. They each have their own parts supply next to them. Whatever they stock them with is what gets put on that side. You do want to have more than one supplier, but some engines may still get all NGK and other get all Denso, some get a mix.

 

Same, I have never heard of duals being on one side and singles on the other. That’s not right. Someone else must have swapped one side.

 

When I got got th truck in 2003 it had 26k on it and no work had ever been done to it other than the oil changed. To the life of me I can not think of a time I would have had someone work on the engine other than the timing belt and water pump. Seems weird they would have only changed one side though....

 

6 Densos came out, 6 Densos went back in. Never had a problem. NGK wires though.

 

My 1997 had 181k miles on it when I finally decided to change them, and the wires due to reduction of mpg's.
Went from consistent 18-19mpg, down to 16mpg over a course of about 20k miles or so.

3 Densos and 3 NGK came out, 6 NGKs went back in.

At 218K miles now, getting 18-19 mpg.

 

Were the singles on the passenger side? Was there a white mark on the tip of all 6? I'm thinking if the 3 singles were in the passenger side, they were changed out because they were easier to access.