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MD-80 PILOT
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Discussion Starter #1 (Edited)
I've always found it interesting the factory installs NGK on one side and Denso's on the other. I'm not sure if or why the Engineer's would design the engine that way. I find it hard to believe this is not done intentionally. I guess if anyone who has changed their plugs on a Mexican built Tacoma would chime in...this would certainly answer the question if this was the intension of the Toyota Engineer's or just the way the plugs are installed at Nummi. Check out this thread...I find it interesting to see how the NGK vs Denso plugs respond to the same engine. It seems to me the NGK's run rich and the Denso's run leaner. I think when I replace mine at 30K...I may just spend the $12 on the Denso iridium's.

http://www.toyotanation.com/forum/t194813.html
 

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MD-80 PILOT
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355 Posts
Discussion Starter #3
Actually, the Tijuana plant started out making the composite beds but now produces approx 30K+ fully assembled Tacoma's. Also, from what it sounds like maybe more in the future. Evidently Toyota management in Japan is concerned about the escalating costs over at Nummi.

http://www.signonsandiego.com/uniontrib/20050202/news_1b2toyota.html
 

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i <3 Toyota
2007 Tacoma X-Runner
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199 Posts
Can't you determine the manufacturing country by the VIN number?
 

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MD-80 PILOT
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355 Posts
Discussion Starter #5 (Edited)

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Registered
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Denso

My Denso iridiums are being installed monday morning. I heard there is a bit of a performance boost from using them. We'll see. . .:smokin:
 

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Humble Servant
2012 DC PreRun Auto
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1,158 Posts
It may have the appearance that the NGKs run rich, but I can't think of any way that the plug can affect the mixture and make it rich. (I guess, a long shot, would be if it did a poor job of igniting, that excess O2 might cause the ecm to add fuel, but that would likely affect all cylinders.)

More likely that the NGK may be a bit colder than the Denso, or some other phenomenon of differences in surface finish or coatings that would make precipitants form on the NGk more than the Denso. Another possibility may be differences in the engine itself, from right to left bank ? Thoughts?
 

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MD-80 PILOT
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355 Posts
Discussion Starter #8
Same fuel, same ECU, same type coil packs..different looking plugs. This not only the case with Pb plugs, but with others who have replaced there plugs as well. It seems to me the Denso's for some reason are running hotter and maybe the copper electrode is of a different grade(different thermal properties); resulting in the igniting of the combustion at a slightly hotter temperature? I wouldn't think a finish or coating would make a big difference with respect to the appearance of a more cleaner and leaner looking plug...but then again...who knows..I've heard of stranger things.


msibille said:
It may have the appearance that the NGKs run rich, but I can't think of any way that the plug can affect the mixture and make it rich. (I guess, a long shot, would be if it did a poor job of igniting, that excess O2 might cause the ecm to add fuel, but that would likely affect all cylinders.)

More likely that the NGK may be a bit colder than the Denso, or some other phenomenon of differences in surface finish or coatings that would make precipitants form on the NGk more than the Denso. Another possibility may be differences in the engine itself, from right to left bank ? Thoughts?
 

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Denso's

My Denso Iridiums are going in tomorrow morning. If they run hotter, i'm glad because I need all the help I can get at 7000 ft. above sea level. I guess 45,000 miles is a good time to change them.:hammer:
 

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Toyotanation
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6,972 Posts
Do you think the type of plug "Denso" would noticeably make a difference in MPG?

But that still would not do anything to explain why they use two different types on the same engine.:dunno:
 

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MD-80 PILOT
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355 Posts
Discussion Starter #12
If one plug is burning significantly leaner than the other...I believe it could make a difference.

toku58 said:
Do you think the type of plug "Denso" would noticeably make a difference in MPG?

But that still would not do anything to explain why they use two different types on the same engine.:dunno:
 

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Black V6 6pds AC
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How do you determine ifa plug set is burning too hot?
 

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Surfing TN via iPhone
05 Tacoma DC 4x4 TRD
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Google Spark Plugs. There's some info about how to "read" a used spark plug.
 

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Humble Servant
2012 DC PreRun Auto
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flyman767 said:
If one plug is burning significantly leaner than the other...I believe it could make a difference.
But again, the plug may be "hotter" or "colder" but it is not likely to have any effect on mixture (lean or rich). A slightly colder plug might accumulate the deposits without fouling badly and (noticeably) adversely affecting performance.

As to why???
Perhaps it's a simple economic issue- maybe Toyota has supplier contracts with both so as to avoid interruption of Toyota production if there's a prblm at either of the plug manufacturers. In order to maintain the contracts, they purchase/install the same number of plugs from both vendors (unless one has a production interuption). Instead of using one plug one day and another the next, they find it just simpler to load one line (side) with one and the other w/ the alternate. I've got no other guess as to their reasoning.
 

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MD-80 PILOT
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355 Posts
Discussion Starter #16
True, a colder plug will collect more deposits. Also... another possible explanation is the inherit design of the electrode itself. Someone else just replaced the stock ngk's and denso's and said the electrode on the stock ngk's were somewhat smaller and more rounded off than the denso's. Maybe, this is why the ngk are running colder due to the fact the fuel(due to the design of the electrode) is being ignited sooner?

http://www.toyotanation.com/forum/t200973.html




msibille said:
But again, the plug may be "hotter" or "colder" but it is not likely to have any effect on mixture (lean or rich). A slightly colder plug might accumulate the deposits without fouling badly and (noticeably) adversely affecting performance.

As to why???
Perhaps it's a simple economic issue- maybe Toyota has supplier contracts with both so as to avoid interruption of Toyota production if there's a prblm at either of the plug manufacturers. In order to maintain the contracts, they purchase/install the same number of plugs from both vendors (unless one has a production interuption). Instead of using one plug one day and another the next, they find it just simpler to load one line (side) with one and the other w/ the alternate. I've got no other guess as to their reasoning.
 
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