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2007 Silver FJ ~130k
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Discussion Starter · #1 ·
I have an '07 FJ that has 120k miles on it. The spark plug change interval is every 30k. I have had various dealers change the plugs every 30k. Since I am now retired, I decided to change the plugs myself. Watched a YouTube video and the change did not look too hard. I've done plenty of plug changes in the old days. Everything went smoothly on my FJ until I got to the #6 plug (I think that is correct. It is closest to the firewall on the drivers side.). Access was not too challenging; however, when I put my 5/8ths plug socket in the hole, it won't grab the plug. It just spins. I shined a flashlight down the hole and there is a plug down there and the car was running fine. The other five plugs are the correct Densos for my model and came out fine with the 5/8th socket, but it appears the 5/8ths is too small for the 6th plug. I tried some of my bigger older plug sockets, but they are too big for the hole. Any thoughts? I just ran out and bought an 11/16ths deep socket, but ran out of daylight until tomorrow.

Any help would be greatly appreciated.
 

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The conversion of spark plug hex size 5/8 inch is listed as 16 mm. However, 16 mm is slightly larger than a 5/8. Maybe the plug in the number 6 position is slightly above tolerance, so the 5/8 won't fit. 5/8 inch converts to 15.875 mm.
 

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Discussion Starter · #5 ·
Thanks to all who offered suggestions. I took the problem to the dealer that installed the plugs. The blockage turned out to be the rubber insert from the techs socket. It was old and dried out and stuck to the plug when he removed his socket.
As an aside, I did install Denso Iridium TT plugs, #IKH20TT and they seem to work very well in my 07 FJ so far. I will be watching gas mileage carefully. Be sure to gap them at .043. They do not come pre-gapped. The package can be confusing. It can make you think they are gapped at .04. The actual gap of the plug out of the box is .035. Way too tight.
 

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Thanks to all who offered suggestions. I took the problem to the dealer that installed the plugs. The blockage turned out to be the rubber insert from the techs socket. It was old and dried out and stuck to the plug when he removed his socket.
As an aside, I did install Denso Iridium TT plugs, #IKH20TT and they seem to work very well in my 07 FJ so far. I will be watching gas mileage carefully. Be sure to gap them at .043. They do not come pre-gapped. The package can be confusing. It can make you think they are gapped at .04. The actual gap of the plug out of the box is .035. Way too tight.
Not sure where you got your information, but all Denso iridium plugs ARE pre-gapped from the factory, nominally set to 1.0mm (.039"), with a tolerance of .037" - .043".

If your 'measured' gap was .035", that's only .002" (two-thousandths of an inch) beyond the factory spec.

When you initially measured them, did you use a feeler gauge, or the correct spark plug gap gauge with graduated wire diameters? Using a feeler gauge for measuring plug gap will almost always give you a reading 'tighter' than using the correct wire gauge will.
 

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Copper WAS originally recommended way back in '07.

Long-life platinum and iridium plugs subsequently became available, and Toyota progressively used them in more and more of their new vehicles.

The major Japanese plug manufacturers (Denso & NGK) all offer iridium plugs for the earlier 1GR-FE engines that were originally equipped with 'standard' copper plugs.
 

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Discussion Starter · #9 ·
Not sure where you got your information, but all Denso iridium plugs ARE pre-gapped from the factory, nominally set to 1.0mm (.039"), with a tolerance of .037" - .043".

If your 'measured' gap was .035", that's only .002" (two-thousandths of an inch) beyond the factory spec.

When you initially measured them, did you use a feeler gauge, or the correct spark plug gap gauge with graduated wire diameters? Using a feeler gauge for measuring plug gap will almost always give you a reading 'tighter' than using the correct wire gauge will.
Interesting about the difference between a feeler gauge and a wire gauge. I would have thought that .035 was .035 no matter what the gauge. Can you please explain the difference for the benefit of the readers.

Regarding whether the plugs are pre-gapped, I purchased my plugs from Auto Zone and no where on any of the packaging does it say they are pre-gapped. Furthermore, my owner's manual says the plugs are to be gapped at .043. It does not give a range. The difference between .043 and .035 is not .002, but .007. Ergo, the need to adjust the gap.
 

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Interesting about the difference between a feeler gauge and a wire gauge. I would have thought that .035 was .035 no matter what the gauge. Can you please explain the difference for the benefit of the readers.

Regarding whether the plugs are pre-gapped, I purchased my plugs from Auto Zone and no where on any of the packaging does it say they are pre-gapped. Furthermore, my owner's manual says the plugs are to be gapped at .043. It does not give a range. The difference between .043 and .035 is not .002, but .007. Ergo, the need to adjust the gap.
A feeler gauge is only accurate when the 'gap' you are measuring has perfectly parallel opposing sides. Spark plug electrode facing surfaces will almost never be perfectly parallel, which is why you want to use a round gauge pin rather than a flat feeler gauge. The round pin will always measure the minimum gap, not always so with a flat feeler gauge. Actually, this is probably more of an issue when checking the gap of used plugs that will have uneven erosion of the ground electrode, but accurate measurement of a spark plug gap is always done with a round-wire gap-gauge.

Your owner's manual provides the recommended gap for the original copper plugs ... the iridium plugs are factory-gapped at 1mm (~.040"), which is correct for the iridium plugs when installed in your engine.
 

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Copper WAS originally recommended way back in '07.

Long-life platinum and iridium plugs subsequently became available, and Toyota progressively used them in more and more of their new vehicles.

The major Japanese plug manufacturers (Denso & NGK) all offer iridium plugs for the earlier 1GR-FE engines that were originally equipped with 'standard' copper plugs.
Copper was specd for the 07-09 with a 0.043 gap. Running anything else and the FJ runs like A$$. Copper plugs are cheap and easy to replace.
 

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Discussion Starter · #15 ·
"Denso’s gap spec for the iridium plugs is 1mm (.040”) with a tolerance range of .037” to .043”."

Where did you find that information? It is not on any of my packaging and I cannot find it on their webpage. I think that source would be helpful for the other members.
 

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"Denso’s gap spec for the iridium plugs is 1mm (.040”) with a tolerance range of .037” to .043”."

Where did you find that information? It is not on any of my packaging and I cannot find it on their webpage. I think that source would be helpful for the other members.
Flyrod -
I wasn't able to find the chart with the +/- 0.05mm .037" - .043" gap tolerance again tonight, I am pretty certain that it was either on a Denso.com or Densoproducts.com site. Denso.com has websites covering each different global market, and it may have been on a Denso Global site.

The Denso Spark Plug Training Manual has 100 pages of information about spark plug technology, electrode types and materials, heat ranges, ignition system design, troubleshooting, etc.
https://www.denso.com/global/en/pro...e-parts-and-accessories/plug/pdf/t-manual.pdf

Going back and looking for the tolerance info, I did find a Densoproducts page that has a part number decoder for the iridium plugs that define each character ... interesting that the IKH20TT plug is an extremely hot plug, 1 step from the hottest iridium plug that Denso makes.
DensoProducts.com: Denso Spark Plug Numbering System

Here's the detailed spec for this plug ... this is the only place I found that listed the internal resistor value (5K ohms); It also has the recommended installation torque values. Click the 'Product Specifications' link:
Denso 4704 IKH20TT Iridium TT Spark Plug

Here's the explanation behind the recommendation to use a wire gap gauge vs a feeler gauge, but more applicable to a conventional plug vs the fine-wire iridium plugs. If the plug has been used, so the ground electrode is eroded, or if the ground electrode has been bent to adjust the gap, the feeler gauge will indicate a smaller than actual gap ("B") vs the actual gap as measured by the wire gauge ("A").

1145421
 

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Copper was specd for the 07-09 with a 0.043 gap. Running anything else and the FJ runs like A$$. Copper plugs are cheap and easy to replace.
Regarding copper plugs vs iridium plugs, if the spark plug's reach, heat range, total spark energy, gap location within the combustion chamber, resistance value, etc. are all essentially identical, any difference in engine performance will be essentiall unmeasurable.

If changing from copper to iridium seemed to make some easily-felt difference in engine performance, then some other variable was at work, which could have included a defective plug (cracked insulator, etc.).

Before recommending a platinum (or now iridium plug) for any specific engine application, the spark plug manufacturers perform extensive dyno and on-the-road testing to ensure that the 'new' plug duplicates or exceeds the earlier plug's performance. The primary reason the vehicle manufacturers have adopted plugs with precious-metal electrodes is that engine performance, fuel economy and especially exhaust emissions can be maintained for much greater period of time than was possible with copper plugs.

Every Toyota engine that I've worked on that was originally equipped with copper plugs ran better, and ran better longer, when platinum or iridium plugs were used to replace the original copper plugs. That was especially true with the 'wasted spark' V6 engines that exposed each plug to twice as many firing cycles as engines with an individual ignition coil for every cylinder.

I don't think ANY current Toyota, Honda, Mazda, etc. engine uses anything except platinum or iridium plugs
 

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No. Copper core plugs are the best performance plugs for their ability to conduct energy ( copper being the best conductor next to pure silver ) from the coil to the plug (spark), the trade off for this performance if is life expectancy ( 20-30k mi )
All the fancy materials used now (platinum, iridium, dumbotaniuim etc) will extend the life of the plug but the trade off is performance. The exotic metals are less conductive than copper and the material is prone to overheat which affects spark delivery (weaker). This is the reason many of the exotic metal plugs have Ysplit ground electrodes, triple electrodes, notched electrodes etc is to fight this loss....not performance gains as the advertising claims. The other downside of the exotic materials is that it is very easy to mar/scratch them while gapping the plug, once that happens any benefit is lost. Considering that most mechanics have old school tech and thinking- either the gap disk, a set of wires etc - to gap new school plugs chances are a lot of the new plugs installed are ineffective( scratched).

There have been many '07-'09 owners who have noticed/felt the same with the plugs and many here on the forum - hot topic back then. IMO Toyota engineers will recommend what is best for their products and aftermarket will tell you why you should buy their product.

I will continue to run copper - it has served me well the last 14 years and you can run what you want.

Next thing you are going to tell me I shouldn't be running 91 octane in my FJ......
 

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Mikey, I knew you'd want to debate this, but technically you're incorrect.

If the core of your hypothesis is copper plugs are better because of the improved "conductivity' of copper vs platinum or iridium, that just doesn't hold up under scrutiny.

First, the total actual length of all the conductors carrying high voltage in spark plugs is less than an inch. In copper plugs the copper section is maybe 1 inch long, and far, far less than that for the tiny bits of platinum or iridium that are welded-on to the larger pieces of electrode material. With either copper or precious-metal construction, the total resistance of the metal conductors is in the milli-ohm range (thousandths of an ohm).

Now here's where your theory collapses ... both the original 'copper' plugs (K20HR-U11) and the later platinum and iridium plugs are RESISTOR plugs - ALL of them contain an internal 5,000 ohm resistor. This internal resistor completely negates any effect that the thousandths-of-an-ohm (0.001 ohm) electrode resistance has on spark energy or voltage rise time. At the 30,000 volt levels that the ignition system generates, even the 5,000 ohm internal resistor has very, very little effect on spark energy ... the resistor is there to reduce radiated EMI (electromagnetic noise) that couples into audio systems, etc.

To think that .001 or .005 ohms makes any detectable effect on spark a spark plug's ignition performance is like saying that you would be able to see the effect on distance traveled by adding one more drop of fuel to a full tank.

Toyota did not specify iridium plugs with the early FJs because iridium plugs were not available at that time.

I fully agree with you that the tiny 0.4mm diameter electrodes are much easier to damage by attempts to "adjust" the gap, and that's why Denso and NGK pre-gap the plugs and recommend that the gap NOT be adjusted.

Running 91 octane fuel is not MANDATORY for any FJ engine, but potentially you can get a little more power out of the engine, especially if you have carbon deposits on pistons or combustion chambers that might trigger preignition with lower octane fuels. The later dual-VVTi engines were specifically tuned to pick up an additional 20+ HP on 91 octane fuel, but were certified with 89 octane.
 
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