V6 has a miss in it

49,000 miles on my V6 14 DCLB. A couple months ago it had developed a miss at idle. At first, the miss was so bad that I could see the tach jump and you could feel it in the seat. I assumed this was due to lack of use and maybe a sticky fuel injector.

I ran 2 bottles of Gumout fuel system cleaner through it, in 20 gallons, one tank at a time. Each time it seemed to get a little better. Recently I ran a bottle of VP Racing fuel system cleaner through it and it’s a little better, but not gone. The tach doesn’t bounce and you can’t feel the shutter in the seat, but it’s still there.

I had put all new Denso iridium’s in the truck about 15k ago. I don’t notice any miss under load, it seems to only be at idle when stopped and in gear. Has anyone else experienced this?

 

Not to start the whole iridium vs copper spark plug debate but FWIW Toyota spec'd the 4.0 v6 with copper spark plugs and some people have had misfire issues when switching to iridiums. Coppers can conduct better and might be a more powerful spark but won't last as long as iridiums which is one reason they're not used as often. I would consider switching back to OEM coppers, they're super cheap right from the dealer. Or also, where did you get the plugs? Amazon and ebay has a lot of fake spark plugs these days.

49k is quite low mlieage on these to be having an ignition or fuel related issue so I would be looking at something like the plugs or like you said some bad gas.

 

Mine had a miss after 200k+ miles with the original copper OEM plugs, new copper plugs fixed the idle

 

This is my 3rd V6 Tacoma and I switched to iridiums on my first one with no issue, I didn’t have the second one long enough to need to switch. OEM Densos are very cheap at the dealer, you make a good suggestion, especially at the low use my truck gets. If I’m not going to camp, towing my boat, if pulling my trailer for firewood once a year, it sits.

You make a good point about them not having iridium’s from the factory, I hadn’t thought about that. I am very aware about the fake Denso plugs and I bought them from a reputable seller. I also had previously researched the ways to tell which are fake. I’m 98% sure they are genuine.

For the few bucks it costs for copper, I may switch back to try it. It is however odd that the fuel system cleaner has helped the issue, although not resolved it.

 

All good points and I agree I've run iridiums in every vehicle besides this 2nd gen v6 because I couldn't make up my mind after hearing everyone debating it, so figured OEM was safest move lol. Figured it's worth mentioning in case you hadn't heard about it. I would say fuel system cleaner could still make a difference because a lot of them are increasing the octane rating (raises the knock threshold) or improving the combustion characteristics in some way so you may have a cleaner spark burn. Lots of variable but since the plugs are directly what's igniting the fuel they can def impact each other.

Hearing you say it may sit a lot would make me suspicious of gas related though if its a long time between fill ups.

 

Always hard to diagnose this sort of thing without being there... Is it throwing codes? My first response to this sort of thing is always to check the air filter, clean the intake and the MAF.

 

49k miles? Start with simple stuff like cleaning the throttle body

Personally i would put oem copper plugs back in it.. and check the ignition coil boots carefully for any cracks or signs of arcing

And be careful running all that fuel injector cleaner through it. Too much can damage the insulation between the electrical windings inside the injector and cause them to short out. The windings are cooled by the fuel flowing through the injector.. also at only 49k miles thats not really enough time to have a bunch of crud in there anyway..

Scan it for codes and see if there's anything misfire related

Look for any broken or rotted vacuum lines

A leaking purge valve could cause those symptoms. Remove the purge line from the intake and cap off the vacuum port. Drive around for a bit and see if the symptom goes away. It may throw a cel code with the line disconnected but you can just clear it with a basic scan tool

 

You need to find out what cylinder is the one mis-firing before you waste money elsewhere. May be simple, may not be but that is the first step. Next would be fuel or spark being the issue. [barring something really serious like a head gasket]

14's are solid so I'd start with the easy stuff including looking for any chewed wires.

 

Update: I went to the dealer and bought new OEM copper Densos. When I pulled out the Denso iridium’s, with only 4500 miles, I think the technical term is SMOKED! The .044 gap on the Iridium's is now .075+, they are completely shot! I honestly don’t know how the truck ran as well as it did.

I haven’t started it yet, I’ve only changed the passenger side so far. I loaned my extensions to my son and I can’t do the drivers side without them.

 

Yeahhh something isn't right lol. They should obviously be lasting wayyy longer than that. Throw the OEM coppers in and see how they last I guess...

 

Looks like the iridium points came off. They are probably sitting in the cat now. Not good. I've been running NGK Iridiums for about 10 years. They still run flawlessly.

 

Iridiums require more voltage to spark because they have higher resistance. Use copper plugs because it has much less resistance and is what the voltage of the ignition system was designed to use. You can get lucky with an ignition system on the edge of enough voltage to reliably use iridiums but not every time. It's not that hard to change plugs on 2nd Gen 4.0 V6. Regarding resistance, silver will be the least, copper 2nd, then platinum is way down the list (iridium is mostly platinum). They use silver plugs in race cars but only get a few hundred laps on them. Great performers but lousy longevity.

 

I wouldn’t say that the points came off, they look like they burned away.

I was very careful when I bought these plugs to be sure that they were genuine Denso. At this point they are either fakes, or my ignition system just didn’t like them. I had these identical iridium’s in my 06 V6 Tacoma with no issue.

I’ve got one side changed, I’m getting my tools back from my son tonight so I can do the other side.

 

UPDATE: I installed the last of the plugs, the miss is gone and it’s running like a top!

Attached is a picture of the old plugs. Full disclosure, I miscalculated the miles on the plugs, they have 20,250 on them. A little more than the original thought of 4,500, but still way less than the 100,000 they’re supposed to last. They have been failed for quite a while, so the mileage when they failed is not exact.

I sent an email to Denso customer service to see what they say.

 

Glad your truck feels better, but I would still do a bit more diagnosing because iridiums should not look like that after only 20k. I would check the easy things first. Are they counterfeit? As crazy as it may sound, I have seen it before (https://assets.denso-am.eu/production/attachments/Spark-Plug-Counterfeits-Poster-English-upd.pdf). What is the part number? Are they the correct heat range? After that, I would look at your fuel trims. With electrodes worn down like that, you could be running lean. Monitoring fuel trims can point you toward a vacuum leak, fueling issue, exhaust leak, or other problem that could cause the plugs to see hotter conditions than they are designed for, which would lead to the type of wear you are seeing. I run iridiums on my Tacoma and have pulled plugs at 80k that had minimal to no additional gapping from the pre-gapped spec of 0.044 inches.

 

I am familiar with the fake Denso issue and I thought that did my due diligence before I bought them, maybe I was fooled.

According to the part number, these are the exact same plug but with an iridium tip. I can’t comment of fuel curve and I know of no vacuum leak. I would have expected a rough or erratic idle if I had one. I did have an exhaust issue, my muffler rotted out from sitting. I don’t think that I put on more than 30 miles once I discovered that.