05 Tacoma Misfire cyl 4 196k miles

Im gonna swap that coil this week. I didnt mention that when I took it back to the mechanic he did say he swapped plugs and coils with no luck. Whether he did or not we would never know.

I did remove the radiator cap this morning and notice some bubbles when the engine was cold.

Here are my fuel trim numbers with the truck in the driveway. Do I need to drive it to give a more accurate reading?

 

I don’t see anything unusual.
Your engine temp is a bit low, but that could be because it hasn’t run long.

 

anything between -10 and 10 is generally OK, -5 to 5 is better/normal. Given that problem is intermittent, you need to get the STFT 1 & 2 WHILE it is running poorly. some cars will capture freeze frame data when a code is thrown and stft is usually in that. Haven't had any codes on my taco, so don't know if these trucks will provide that. Did you observe the bubbles with the engine running? That would likely point to the head gasket, but don't see that creating intermittent misfires. THis kind of issue has coolant leaking into cylinders at rest (causing white smoke on startup) and while running, it pushes combustion gas into the coolant system and you see the bubbles. Typically the leak needs to be quite bad to push coolant into the cylinders while running and create rough running

 

You have bubbles in your radiator, your year motor is known for head gasket issues, check for that

you can rent a tester, but they are pretty cheap too

$38 Block Tester BT-500 Head Gasket Combustion Leak Test Kit - Made in USA

https://www.amazon.com/Block-Tester-BT-500-Combustion-Leak/dp/B06VVBSFTF/

 

You might want to consider that you have more than one problem going on and are having symptoms that don't have anything to do with each other.
Also, the number of 05-06 trucks with head gasket problems is low, but the number of 05-06 head gasket experts here on TW is high. Start with the cheap stuff and work your way up.

 

Sorry, I zoned out for a few days.

The known "defect" is in the head gasket itself, not the heads. As @TnShooter stated, Toyota changed the design of the head gaskets at some point during '06 model year production, and stopped manufacturing the weaker old head gasket designs at that point. So if you buy a new head gasket from Toyota today, even for an '05 engine, you will get the updated design, and it will permanently fix this problem, if you have it.

To solve this HG problem, if you have it, technically, you don't even need to get the heads worked over at a machine shop, you just need to replace the head gaskets. You could just take the engine apart, clean up the mating surfaces by hand, and reassemble it with new head gaskets, re-using everything else. But this is not recommended for many reasons, and is probably not the way any reputable shop would do it. I should mention, I don't work at a shop, never have, I'm just a shade-tree guy who swapped the head gaskets on my own '05 a few years ago. But if you really wanted to cut corners this much, another option might be to research head-gasket-in-a-can type products, and try your luck there. I have never used them, and can't comment on their effectiveness, but correct application of such a product could potentially reduce or eliminate the problem, without any engine work at all, but it could also later fail, not work in the first place, or even make things worse. The most reliable long-term solution to fix a failing head gasket is probably to replace it. And if you're going to do that, you should probably take the heads to a machine shop as part of the job, for three general reasons:

1. Inspection for damage: Assuming you do have the dreaded HG issue, it has progressed to the point of causing misfires for some time, thus there is slightly increased chance of damage to the heads due to localized overheating. I'm not claiming that your heads are damaged, they are probably fine, but it's best to hear that from an expert who's thoroughly examined your heads vs. random people speculating on the internet.
2. Cleaning and resurfacing: This means that the heads will be perfectly clean and flat to ensure a good seal to the new head gasket.
3. Valve job: This involves replacing the valve seals, reseating the valves, and adjusting all the lifter buckets to correct for wear. This isn't something you'd normally do on these engines, like as normal maintenance, even after 200k miles of use, but that's because it's a pain in the ass to pull the heads. But if you already have the heads off, with 200k miles on them, a valve job will probably improve compression, and may even extend the life of the engine. I'd call this a no-brainer if you plan to keep the truck in the long term.

You can read more about my experience replacing my head gaskets here. This isn't a how-to, but a collection of the key things I learned in the process... with pictures!

There is a specific and well-known head gasket weakness in '05 and early '06 V6s that causes misfires on cylinders 4 and 6, which is not detectable by compression testing.

Checking plugs is a great suggestion, if OP is a novice like me, I would also recommend pulling non-affected plugs, to provide visual comparison. (I have a photo of mine on the above linked thread, but comparing a single plug to online pictures had never been as helpful for me, vs. comparing them to other plugs from the same engine). This would also be a great opportunity to stick a camera in the plug bores to look for coolant in those cylinders! OP, you can get a cheap "boroscope" camera that plugs into your phone or a laptop for less than $20 online. Coolant pooling in cyls. 4 or 6 would provide definitive evidence of a HG leak!

Here is an example cheap-o scope for less than $16, not one that I own or endorse, and probably of exceptionally low quality... but likely also adequate for this task:

$21 T TAKMLY 5.5mm Endoscope Borescope Inspection Camera with Light for iPhone, OTG Android Phone, Snake Drain Scope Cameras Bore Scope Borescopes, IP67 Waterproof 16.4FT Semi-Rigid Cable

https://www.amazon.com/Seesi-Endoscope-Waterproof-Inspection-Semi-Rigid/dp/B07PBF6DX5





The '05 head gasket issue is a really small leak, and it seems that several common diagnostic techniques applicable for major head gasket failures (e.g., after overheating) yield false negatives.

In particular, it doesn't show up on compression tests. I had a bad HG on my '05, and all cylinders still had great compression. For this reason, I also suspect (but can't say for sure) that leakdown testing may not be conclusive here. Finally, I've had negative combustion gas test results on other engines with small HG leaks, and would not consider this test effective for ruling out minor HG leaks. Both times, I tested them at home, then took them to a shop in disbelief, had small bubbles emerging from coolant but always negative CG tests. Both times were bad HGs though.

So, other than checking plugs and scoping cyls, the only other test I recommend to OP is the following:

With the engine warm, like after a long drive, monitor the coolant reservoir for a few minutes, looking for bubbles as the engine idles. Remove the cap so you can see it clearly. And I'm talking about the overflow tank, not the radiator where you shouldn't open it hot!

If you see small bubbles emerge at regular intervals, then you have a HG leak. It's been a while, but I think I had a tiny bubble like once every 10 seconds, but non-stop. That's all I needed (combined with "swoosh" noise), before I decided to tear into it and fix my head gaskets. I would call this result a definitive positive, but would still recommend pulling plugs if negative, given your other symptoms. A minor variant on this test, you can take a sandwich bag or something, and rubber-band it over the overflow cap, assuming it's possible to get a reasonable seal... then go rev the engine and watch to see if the bag inflates.



It's a good idea to do diagnostics, to make sure you don't needlessly embark on a complex and expensive repair. I was quick to jump to my conclusion that it's your head gasket, but others are correct to suggest that it may well be something else... especially given the 300 code.

But I'm still here writing a whole damn novel about head gasket issues, not because I'm certain that it's your problem--I have no idea--but because it's easy and straightforward to rule out, and also important to fix ASAP if it turns out to be the case.

I have discussed three definitive tests that can be accomplished within one driving cycle, requiring at most a modest investment in tools... or a trip to a competent shop. None of these three tests involve reading codes or swapping plugs and coils to see if the problem goes away while you continue to drive.

I'm not saying that you shouldn't continue to drive the truck, just that you should figure out if your HG is bad, as the top priority. Hopefully it's good, but if not, then the sooner you can fix it, the better. It will get worse and eventually lead to major problems. Repair would be ideal, but if you can't afford it, then try to control it with sealant additives in the coolant. If you want to repair it, but need to delay it, then I'd recommend against sealants, but try to minimize needless driving, keep a careful eye on coolant and temps, and consider changing the oil more frequently. Shouldn't be too much coolant getting into the crank case, but over time, I'd be weary about this. But I also tend to overthink things, too.

There is a reason the number of 05-06 head gaskets experts here on TW is so high: it's because these trucks came with a factually defective head gasket design that fails at dramatically higher rates than later model years. I don't know the fraction of engines with head gasket problems, I'm sure you're right that it's "low," but whatever it is, it's a hell of a lot higher than for the all the subsequent engines they made after abruptly switching to a non-defective head gasket design in mid '06 production. It's way higher than it should be, or than it would have been if Toyota didn't overtly botch the head gasket design for the first few years of 1GR-FE production!

I tried to put together a consensus thread, after dealing with this problem myself, hoping to share what I had learned, but also seeking to dispel the notion that all '05s are doomed to head gasket failure. What I got was mostly people reporting failures, and literally only one single person reporting a truck in service beyond 200k miles with working original head gaskets. I even gave it a sassy title hoping to draw in folks with problem-free '05s! I guess a pickup truck forum, where people mostly go to discuss problems with their trucks, isn't the best place to collect data on problem-free trucks... who knew, right?

The frustrating part is that I'm arguing with you here over a point on which we both agree. HG failures are overreported on TW! Would you like to contribute to that discussion? How many miles are on your '05? Are your factory head gaskets still holding?

 

Since I drive truck every day with no issues, the head gaskets are still working.
I'm not disputing the fact that the 05-06 engines have a slightly higher head gasket failure rate than other years. My complaint is that you lump all 05-06 vehicles in this category. Why don't you say "don't buy ANY Tacoma because the frame will rust out". That way you would not encounter the head gasket, or any other Tacoma problems.

 

Not sure I follow. Did you read the thread I referenced above? To be clear, I titled the thread "Don't get an '05" to entice folks to jump in and defend the '05s. Not because that's what I actually believe or want folks to think.

The whole goal was to dispel the notion that folks shouldn't buy 05s, because they're actually great trucks, just with certain known weaknesses vs. later years, which can be easily addressed through proactive maintenance.

I'm asking you what mileage you've gotten up to... specifically because you have an '05 with factory gaskets running strong. I am seeking examples of folks that have problem-free '05s getting to high mileage, to cite as evidence that not all '05s are doomed to head gasket failures.

Or was this 4.0 vs 2.7 issue I overlooked? Your signature only says 2005 Prerunner, guess I assumed you had the V6.

Sorry for the confusion... I definitely didn't mean to pick an argument with you.

 

Just to update this thread. My truck did have a blown gasket. Compression on cylinder 6 was low.