05 Tacoma Misfire cyl 4 196k miles

Hey guys. Hoping to get some insight. Back in March was experiencing misfires at cyl 6. Cel read p0300 and p0306. I changed all the plugs and that temporarily solved my issue for about 3 months until the cel came back with the same codes. P0300 and p0306. There was a little bit of oil on 2 of the coils. I cant remember which ones. Couple drops. 3 months after the plug change the Cel came back on p0306. Finally brought it to my mechanic and he recommended to change the coils. He put on Hitachi coils. The misfiring was still happening. Engine jerks around 50mph when gaining speed and continues to around 70mph. I brought it back and he said he couldnt figure out what else was wrong. He did a compression check for me and says it was good. He didnt tell me the numbers. Said he’s done all he could. So I took it from him and the truck ran bad on the fwy for about 30mins then it seemed to have cleared itself out. Ran great for two weeks. Well, now I have cel p0300 and p0304. Im obviously not taking it back to him. Hoping to get some advice before I try another mechanic.

 

You have a 304 and a 306 now?
Or just 304?

 

Edit: Sorry, I forgot that you posted your mileage in the thread title. Oof... 196k? x2 on my unfounded conclusions. Sorry!


I'm not an expert on diagnosing these codes, and you didn't post mileage or other engine history, so take this with a grain of salt... but when I read about an '05 V6 with a misfire, especially on cyl. 4 or 6, my mind immediately goes to head gasket issues.

I tried to summarize this issue here:

https://www.tacomaworld.com/threads/“don’t-get-an-05-”-deficiencies-and-solutions-to-early-2nd-gen-problems.735957/

There may be better references on this forum, but this is at least a good starting point.

I'm not saying this is your problem, but it is something you should be aware of as part of your diagnosis procedure. It won't show up on a compression test, and may or may not show up on leakdown or combustion gas tests.

I'd listen for startup "swoosh" sounds, watch the tailpipe at startup, and watch the coolant reservoir for bubbles at operating temperature.

No single test is conclusive, and in general, you should do a lot more diagnostics before tearing into an engine for a head gasket job than I am recommending in this specific case...

But in this specific case, you are not looking for "beyond reasonable doubt," you are looking for the slightest shred of a clue, because you have an '05 V6 and it is has already been tried and convicted of having an inferior head gasket design, so the only question is whether or not your truck has yet served out that sentence.



Important note: If your head gasket has already been properly replaced with the newer design, then your engine is no more prone to head gasket issues than any other 1GR-FE, and you should definitely dig deeper on the diagnostics!



Good luck!



Edit: Welcome to TW! Hopefully I'm wrong about your engine needing this vastly complex and expensive repair. But don't worry! Folks like me, or possibly even people with actual knowledge, are lurking around this forum, to provide useful suggestions as you work your own way through the process of denial, acceptance, repairs, and most importantly, exuberant upgrades!

 

Just the 304 along with the 300.

 

Id check all your vacuum lines with a p0300 code

 

Oh boy. I do have that swooshing sound at start up. From what Ive read the past few months, that it could be a head gasket repair. Ive already accepted this and ready to pay. I just hope the next mechanic doesnt go on a wild goose chase eating into my wallet. Lets just get it over with. Thanks.

Edit: Im also in SoCal so if you know of any good mechanics, send them my way. Near LA and OC.

 

Maybe valve cover but more importantly spark plug tube gaskets.

 

Well, that sounds like the slightest clue to me. I wish I had better news, but this jury hereby finds your truck GUILTY of having minor head-gasket leak. Unless, like I said, your engine is either a more modern swap-in, or has already had the HG job.

Again, in any other case, I would recommend further diagnostics. But in this case, I genuinely believe you're on the right track to tackle this ASAP, and not waste any more money on diagnostics. Props to you for preparing for it.

The good news is that this is a solvable problem, either on your own, or through a shop... and your repaired engine will be every bit as good any other Tacoma on the road!

Can't help on a full-service mechanic, but if you are going to tackle it yourself, here's a great shop to get the heads reworked:

https://vapengines.com/

I used them for my own HG replacement, they did great work!

 

Have you checked the coolant level in the radiator?
Have you pulled the plug after it has sat over night and inspected the cylinder for coolant? (Youkd ned an inspection camera)

 

What sort of a head gasket leak would cause a continuous misfire like this that wouldn’t show up in a compression test?

OP, I’d check the plugs in those two cylinders to see if they’re fouled in any way. I don’t know about you, but I wouldn’t know what a swoosh sound is without having one pointed out to me on a known bad engine. The fan clutch noise at start up could be mistaken for that if you don’t know any better.

 

I havent noticed the coolant levels drop too much but only cause I dont drive the truck more than 3 times a week, if that. If I start it up after 3-4 days I have rough idling for most of the day at stop lights etc. There are times I drive the truck regularly and it seems the issues go away but maybe cause Im burning off that water? No noticeable white smoke out of the exhaust in the mornings.

 

Swooshing sound, sounds like theres 5 gallons of water in a jug behind the passenger side dash.

 

Do you have a camera you can get down the spark plug holes?

 

Unfortunately I dont. Never saw the need for one cause I dont do extensive engine work on my truck. Just brakes, oil changes. The easy stuff.

 

If I have my heads machined, would the same problem arise or would the machining process eliminate the known defect?

 

I'd figure out whats actually causing you're issue first

 

This….,,,,

But to answer the question.
The head gaskets were updated in late 06’. So the new gaskets would fix the issue. That is, if it’s your issue.

I don’t care for aftermarket electronics on Toyotas. I’d swap coil 4 with coil 1 and see what happens. Hopefully the miss moves to 1.

I think the p0304 will remain. But maybe you’ll get luck with a bad coil.

 

^^^
Easiest way to rule out a bad coil

 

Ill give that a try this week. Thanks.

 

Good to check, as #4 coil is suspect. However, the 0300 code is for random misfiring that the computer doesn’t get enough repeatability to nail down a particular cylinder like it did for #4. Sometimes it sees the misfire, but cannot figure out which cylinder it came from. After all, it is trying to figure this out from changes in crank sensor data and dealing with speeds derived from triggers microseconds apart. When they can’t figure it out or is bouncing around different cylinders, they throw the 0300. A common cause of p0300 is a lean condition,often from vacuum leaks. Need to get a scanner on the truck and watch the fuel trims while the engine is missing. If the trims go up (positive numbers), that is lean. If the fuel trims are close to zero, ignition is the more likely culprit. Given that rough running is intermittent, another possibility for lean conditions is a failing fuel pump that occasionally drops pressure or a failing pressure regulator.

head gaskets are pretty far down the list of culprits for misfires especially intermittent ones. Find a new mechanic. Your guy gave up WAY too soon. Swapping coils then giving up is kind of sad for troubleshooting a misfire.