Iridium plugs in a 2nd gen 6

Why aren't people using Iridium plugs in their 2nd gen 6 cylinder engines? I keep reading the the old fashioned plugs that last 30K miles are just fine, but that makes no sense to me when the cost difference for all 6 plugs is less than $10. Is there some technical reason not to use the iridium plugs or do people have more time than I do to perform boring maintenance on their truck?

 

I ran Iridium plugs for 20K...I hated them. MPG's dropped, engine felt like it was being strained.
Took them off, replaced with Copper.....everything went back to normal. I'm not the only guy that has experienced this.

Edit: Not even 20K....I might have taken them off at <15K

 

Which ones did you use?

 

Have only used Denso Copper/Iridium

 

It's my understanding that Toyota put Iridium plugs in Super Charged 4.0L engines. Some believe this was done because of the increased complexity accessing the plugs with an SC setup- once every 120K vs. once every 30K.

If that's why it was done, why would these Iridium plugs not work in any other 4.0L engine?

In other threads at tacomaworld.com, I've read success stories by folks who ran Iridiums in the 4.0L and others professing failure with their use.

Makes me wonder if, in some cases, the wrong plugs were used or the gap was tinkered with.

 

There is actually a sticky thread on spark plug discussion, randomly read it last night.
https://www.tacomaworld.com/threads/the-truth-about-spark-plugs.152726/

From my understanding Iridium plugs will last longer than conventional plugs. But Iridium plugs aren't as conductive as your standard copper plugs, so they won't produce quite as hot of a spark. Should this actually make any difference performance wise I really doubt it if you've gapped your plugs properly, but there is only one way to find out for sure.

 

I just pulled the trigger on the iridium plugs. We'll see if it makes a big difference in performance or anything else. (my bet is that iridium plugs will be indistinguishable from copper plugs) I'm not too worried about the conductivity of iridium vs copper because copper is second only to silver in that measure. Also that measurement depends on what the metals are alloyed with. Pure copper beats pure iridium, but copper/nickel and iridium/platinum are about the same. And given a spark is a spark, if the ignition system has enough umph to push the electrons across the gap it will be plenty hot to ignite the fuel air mixture.

 

So today I installed the iridium plugs. I hope they work out because I really do have better things to do than change plugs.

The old copper plugs have about 40K miles on them and were worn from he initial .040 gap to .053. The iridium plugs were all gapped from the factory at .036 and I bumped them up to .040 to be within the range recommended by the factory. When I fired it up for the first time it ran like crap and threw a check engine light at me. My first thought was shit the internet was right these plugs don't work! My second thought was you dummy did you plug everything back in? After connecting the #2 cylinder coil pack the engine ran like normal. And, after running some errands the check engine light went out. As far as the butt dyno is concerned I couldn't tell any real difference. Maybe a little peppier, but it's hard to tell. After I run a tank of gas through it I'll report back. My bet is little or no difference.

I also crawled down the rat hole of spark plug resistance a little further and IMHO it is a non-issue for modern street driven cars and trucks. From the NGK web site:

I measured the resistance of the old copper and the new iridium plugs and they were within a few ohms of each other at 5,000 ohms give or take. Clearly the built in resistor pretty much overwhelms any difference between copper and iridium.

Bottom line - why doesn't Toyota go with iridium plugs from the factory? Your guess is as good as mine, but if you follow the money I'm betting that the $10 ish cost difference is a big part of it.

 

Here's a little something to consider. I'm sure you will have little or no performance difference but have you thought about what might happen when you try to remove these after let's just say 100,000 miles and perhaps six years or more. Some folks have had to pull the head to get stuck broken plugs out after extended use. I just change mine at 30k intervals. That's at least two years between changes and it takes me about a half hour to do. It's also a chance to read the plugs and maybe catch a problem before it gets worse.

 

I'm not worried in the least about the plugs getting stuck in the heads. The old ones had 45K miles on them and they came right out. I doubt double the distance will make much difference. Of course, I use anti-seize on any thread that I might want to take apart again. And, I use a torque wrench to get the exact 15 ft/pounds required. Did the guy that had the problem do all that? Or did he screw them in dry and crank them babies to some crazy torque?

As for reading the plugs, I guess that's still a thing. Any modern vehicle (1996 and newer) has a computer that's going to tell you right away if something is going wrong. I love how the spark plug reading charts all include a picture of a "leaded" plug, cause you know how easy it is to buy leaded gasoline nowadays.

I don't fault anybody for changing their plugs, it's your truck do what you want. But, my time is worth a lot and all of the reasons for not using iridium plugs seem to be based on old wives' tales and pseudoscience.

 

The trucks ignition system was designed for copper plugs. Iridium needs a hotter spark. This makes sense to why some experience subpar performance when running iridiums. Maybe closer gap would help, I dunno?

I'll stay with copper. I can handle 30k plug changes cause I luv my truck and the power it has.

My other two cars run Iridium, but the ignitions systems were design for that and I'll spend the $$$ as they are the proper fit.

Just sayin.

 

I don't see that as an issue really. I bought a 2005 DCLB two years ago with 117k miles on it and had no trouble getting the plugs out. Just be sure to put anti-seize on the threads.

 

Fine wire plugs will not make any "performance" difference as compared to conventional nickel/chrome fat wire plugs--anyone that claims they do is full of "it". They will however only have to be changed each 80k to 100k+ miles--so make sure to use never-seize and torque them properly (correct torque is vital for plugs that will be installed for 100k) so that when you do want to take them out they will come out.

There is no such thing as a "pure copper" plug, copper electrodes wouldn't last 20 miles. The copper in "copper plugs" is used as a core material to assist in dissipating heat, the actual electrode in so-called "copper plugs" is made of nickel/chrome alloy. Copper cores have been used in spark plugs from all manufacturers, regardless of electrode material, for 40-45+ years.

NGK's marketing department made a big deal about it and IIRC trademarked the "Copper" spark plug brand name back in the 70s; but even then most makers were using copper cores. NGK just decided to highlight that they did too to try and make their plugs stand out.

 

What makes you as think iridium needs a hotter spark? And, what is a hotter spark anyway? The coil delivers 40K+ volts across a 0.040 gap, that's going to be plenty hot to ignite the mixture. Both copper and Iridium plugs have a 5,000 ohm resistor built in, and if you look closely at the iridium plugs there are only two tiny pieces of iridium, so any discussion about the relative resistance of the two materials is moot.

There comes a point where marketing wank bumps up against science. IMHO what it really boils down to is the cost difference between the two. I paid an extra $1.40 a plug or 8.40 for the whole job. Buying in Toyota manufacturing quantities who knows what the difference is, but even if it only costs $1.00 more per truck over the years of manufacturing that amounts to a million or more dollars of profit. (I don't know how many Tacomas have been made, so what ever that number is is the savings to Toyota.)

 

Most COPs (Coil-On-Plug) are capable of ionising just about any gap any plug is likely to have--this is why they will fire conventional plugs with worn gaps you could "drive a truck though" (the problem with that is there will come a time the coil is so overloaded it will burn out.

Here is a video of a Ford coil-on-plug (COP) firing across a 16 mm (5/8") gap



The COP shown in the video is being fired manually by a coil tester of my design (see below). When firing across the 16 mm gap the coil is dumping 100% of its energy, something that never happens in service firing across a 0.050" gap. A rapid sequence of 7-10 firings across the 16 mm gap will make the coil so hot you cannot hold it in your hand; 12 to 15 will make it start to smoke; 25 to 30 will burn out the coil.

Here is my tester, using a triggering circuit identical to that used in 99.44% of modern ignition systems, and affectionately known as COPTesto--the Destructor for its abilities:



A coil's maximum output can be determined and compared to others by determining the maximum gap it can ionise and fire across. Eight Ford OEM COPs were tested and found to fire across a maximum gap of 16.8 mm, 55.4 kV output.

Eight Accel High Performance "Super Coils" were also tested; the best they could muster was a fire across a 15.2 mm gap, 50.2 kV out. So much for flashy yellow aftermarket "high performance" lies. I burned out a set in less than 10k miles on my '03 GT...

 

I'm not sure what you're saying, but it seems to be based on science rather than marketing wank so I'm inclined to like it. A 15mm gap is over 1/2 inch and about 15 times bigger than a .040 gap. Based on the size of a spark plug I don't see how you could even get a 15mm gap. I can say I've never seen anything that big.

What does your tester show with real world gaps of .039 to .043? And can it test the difference between plugs?

 

I agree, it is not possible to "gap" a spark plug to 15 mm. I used an adjustable gap spark tester (a tool well worth having) to determine just exactly how wide a gap various coils could fire across--specifically a Lisle 20700 tester (

$20 Lisle 20700 Coil-on Plug Spark Tester White

$20 from Amazon). Using this tool to check ignition output will 100% separate good coils from bad, any "good" coil should be able to spark across a 10-12 mm free air gap.

In terms of voltage requirement to ionise the gap and maintain a spark, a 0.004" difference in gap on new plugs would be insignificant and un-measurable, It would also have little to no effect on engine operation or performance--even if the increased gap were the result of electrode erosion any differences would be minuscule.

When a spark plug fires the voltage across the gap is as shown below. This is actually the coil primary voltage, which mimics the secondary voltage but is easier and less dangerous to monitor--in this trace each vertical division represents 50 VDC, each horizontal division is 1.0 ms:



At the far left beginning of the trace the voltage at the "ground" lead of coil's primary winding is +12 V, this is because the coil control circuit in the ECM is open; with no current flowing through the coil voltage at the grounded/switched the +12 V being applied to the primary's other lead registers at the lead to be switched to charge and "fire" the coil.

In the center of the trace you cans see that the primary's "ground" lead has been connected to ground by the ECM. This begins charging the coil (building up a magnetic field in the coil's iron core).

2.3 ms later the ECM breaks the ground connection and the magnetic field collapses generating voltages in both the primary and secondary windings--in this trace the ionisation spike in the primary is about 200 V; generating some 20 kV in the secondary winding and thus ionising¹ the air/fuel mixture in the gap so that electricity can flow through it, making a spark.

After the gap is ionised the spark happens, initially requiring 5 kV or so the voltage to sustain the spark drops to 2500 V for most of the spark event that lasts 1 ms give or take.

Once the spark is over any remaining power in the coil dissipates, this is the "ringing" seen just after the spark occurs.

As evidenced above it takes 20 to 25 kV to ionise the air/fuel mix in the plug gap (for high compression and f/i engines this can be higher running 25 to even 35 kV). Ionising the gap requires more voltage with "fat wire" electrodes than with "fine wire" (platinum or iridium) electrodes, and more voltage with eroded electrodes than with new.

These numbers are damned near universal for any mass production gasoline fueled ICE.

It is erosion of electrodes that pushes up voltage requirements as spark plugs age, with the loss of sharp edges (sharp edges require less voltage to ionise the gap) being just as influential as a widened gap. A recent posting here showing a conventional plug with 45k miles on it reveals extensive gap erosion as compared to a new plug:



That level of electrode erosion alone probably drove the ionisation voltage requirement up by 10 kV with the increased gap requiring another 5 kV.

Here are the ionisation voltage requirements for "fat wire" conventional plugs (24 kV) and various thin wire precious metal plugs (20 kV):


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¹ - The high voltage charge causes electrons to be attached to molecules of the air/fuel mixture making it electrically conductive.

 

Dang I stand in awe

I think in one post you pretty much blew up all of the arguments for staying with "copper" plugs.

So, iridium plugs take less voltage to fire than copper plugs. Which makes sense based on this statement.

Everything you say makes sense. So far I've only driven about 100 miles on the new plugs but if there is any difference I can't tell with the seat of my pants. The next test is gas mileage. We will see if there's a difference and I'm open to any result. But, my hypothesis that there is no performance benefit for iridium plugs would say there will be no change.

 

Fine wire plugs can cause the ignition timing to slightly advance (the actual point in at which the plug fires, but just very slightly) because the gap ionises and the spark happens a bit faster. I have only experienced this once, platinum plugs made my supercharged '93 Miata ping a tiny bit at full boost (22.5 psi) as compared to conventional plugs...

 

Wouldn't the knock sensor just retard the spark if that were a problem?