I'm just figuring that out now so bear with me if you knew why all along.

Its a waste-spark ignition system that uses a negative (-) to positive (+) spark on one plug and the other side fires with opposite polarity: positive (+) to negative (-). Since some spark plugs have a special tip made from precious metals (like platinum) and that metal is expensive of course some plugs are made with the special tip on the electrode and some have it on the tip. Or some have it on both the tip and electrode (like double platinum plugs). The direction of the polarity effects which side the plug wears out first and the special tip reduces the wear of the plug. I knew that from my welding experience, some welding is done electrode positive and some is done electrode negative.

So, (maybe) that's why Toyota sent out the 5VZFE from the factory with one type plug on bank 1 and a different plug on bank 2.
Edited:

More info: http://findarticles.com/p/articles/m...07/ai_n8876015

So I guess when replacing the spark plugs on the 5VZFE we need to either get plugs the special plating on the correct side or get special plating on both sides. Probably the double plated would be best so you don't get them mixed up.

Now a question. Does anyone know if the Denso iridium plugs have iridium on both the tip and the electrode? I suspect they are not because I've noticed more tip wear on my drivers side plugs.

 

I'm pretty sure the factory plugs were neither iridium nor platinum--just standard $2 or $3 NGK BKR5EKB-11 plugs on one side and the Denso equivalent K16TR11 on the other. I have read more than once that the only reason was that Toyota liked to multi-source their plugs and subsequent changes could be all one, all the other, or half and half. My '99 Toyota FSM states that either may be used and no suggestion that either is better in one bank or the other. There is also this sticker on the engine that says single-ground=bad and dual-ground=good. I have just used the cheapo OEM dual-ground NGK's for ten years, changing every 30k, and I'm very happy. I have read many posts suggesting to stay away from platinum/iridium in these motors but I can't say why. I also like looking at my plugs every 30K, obdII or no obdII. I think new plugs make my motor happy.

You got my curiosity up, however. The NGK Laser Platinum BKR5EKPB-11 is platinum on center electrode and single ground and so is the Denso equivalent, according to the company websites. The iridium plugs for both companies appear to be plated only on the center tip and are also single ground. So if you go this route, I guess you should go with platinum and not iridium.

 

My mom's 99 4runner had denso's in teh driver side i think and ngk's in the passengerside... when i changed them..

i put ngks in all of them, whichever plug was in teh manual, but it did have two prongs

i bought the same ones for mine..

 

yeah i read that article and what i got was that the system sends the traditional polarity spark to the cylinder under the compression stroke while sending the reverse polarity spark to the oposing cylinder in its exhuast stroke. Then it would switch so the oposing cylinder while under its compression stroke would get the traditional polarity spark while the first cylinder would then get the reverse polarity spark because it would be in the exhuast stroke. So the spark plugs get both spark polarity run through them. Its not resonable to have 2 different spark plugs for 1 motor. Unless its a p.o.s ford that was a 4 cylinder and had 8 plugs, 4 on intake side and 4 different plugs on exhuast side but we wont get into that garbage. And i'd think if toyota truly did design for 2 diff plugs there'd be an additional sticker next to the dual ground sticker saying it calls for 2 plug types. My parts guy at the dealer gave me all the same denso plugs for it. But i'll ask to verify.

 

As far as I heard through TTORA and other forums the heads were manufactured in two different assembly plants and thus came with different spark plugs.

Is says specifically in my owners manual to use only twin ground electrode plugs.....I'm fairly certain that I've seen something about not using platinum plugs on the engine.

Toyota just gives you 6 Denso dual electrode plugs, same that came in the pass side head.

 

Hummm...I'm not getting that, let me post a quote and read that part again.

 

Don't over complicate that each plug fires twice per cycle..exhaust and compression...This is why they are dual ground,beacuse if not a single ground plug would wear twice as fast..Now the polarity voltage issue..it dosen't matter if its ground or source switched as long as it can jump the gap.It's going to wear on both the electrode and the ground..obviously having more than a single electrode would not work..hence the dual grounds on the plug.

 

I understand that

I agree both will wear, but one side wears more than the other. From my DC welding experince the direction of the flow of electrons (polarity) heats one side more than the other. Here is a reference to that: http://www.tpub.com/content/aviation.../14018_653.htm

So if I can transfer that welding theory over the spark plug theory correct me if I'm wrong please. With straight polarity the flow of electrons is from the electrode to the ground, which creates more heat on the tip (ground). With reverse polarity the flow of electrons is from the tip to the electrode which heats the electrode more than the tip. All of this assumes the ignition system is DC, am I wrong about that?

 

That would agree with what you're seeing with your spark plugs.

 

You can always install platinum electrode double grounded plugs for longer service life if you like.

http://www.sparkplugs.com/more_info....72596&pid=2708

http://www.sparkplugs.com/more_info....72596&pid=9642

 

I did find a Denso iridium plug with a platium ground electrode:

http://www.globaldenso.com/en/produc.../features.html

So, I guess the Denso IK22 that I'm running now are nothing special on the ground side of the plug. That maybe why the ground side is wearing so bad for me on the drivers side bank. I guess that may be the reason some are recommending a dual ground plug. I'm just using these IK22 plugs because URD recommended them for supercharged 5VZs. But I think these motors need at least a dual platinum plug, for boosted motors anyway.

 

Here's an interesting link: http://au.geocities.com/ozbrick850/e...boschplat.html

quoted from abouve link:

Again it seems to me the dual platinums would be the way to go. But apparently single plats are bad. And by dual plats I mean plat on the ground and center electrode, not dual ground straps. It appears to me the only purpose of the 2 or 3 ground straps is to prolong life of the plug by sharing the duty.

 

It appears the Denso dual Iridium/Platinum plugs are sold in Europe under the names Iridium Tough and Iriduim Plus 2, see here: http://www.denso-europe.com/Iridium-...000000001.aspx

 

No. Dale is correct on this point. The spark polarity of a particular spark plug remains constant, either always standard or always reversed. This is confirmed by the presence of a diode in the coil pack secondary circuit.

 

Here's the difference between the Denso IRIDIUM POWER and IRIDIUM TOUGH: http://www.globaldenso.com/en/produc...ough/qa_5.html

 

ignore this post

 

Mt.Goat Do you use dielectric grease?
if not this could be an issue causing the wear the way it does!

 

Yeah on the outside of the plug, but what would that have to do with wear of the ground strap (in the cylinder head)?

 

honestly for some reason I was hearing your statement wrong!
I thought you were talking about the top wearing for some odd reason!

well in this case I may suggest running a two step cooler plug!
I have been running the NGK BKUR7ET I have been getting them at Advance
they employ a copper electrode and triple ground strap!
these plugs were suggested for forced induction but I have had good luck with them
in my normal aspiration eng!

 

They are 2 steps cooler LOL.