Hi so over the past month or so my runner developed an intermittent misfire. It eventually got bad enough to run a code as P0303 Cylinder 3 Misfire, i didn't think it was anything serious because i would drive it some more and the engine would smooth out and start performing somewhat normally, maybe just a little down on power. Sometimes i'd start it up and it would idle smooth, but when warm it would start shaking and missing.

I figured the problem was either electrical or fuel because i could get the problem to go away for a bit intermittently. Well, i took it in to a shop and they did a leak down test and isolated the problem to what they think its a flattened valve on cylinder 3. All fuel injectors were supposedly flowing pretty good.

So my question is, what would you do if this were your truck? My dad knows a good machine shop and he thinks i should take the head off and get the valves redone.. I'm kinda thinking i should just replace the whole cylinder head all together with something like this :

2 TOYOTA Tacoma Tundra 4Runner LandCruiser 3.4 DOHC#5VZFE CYLINDER HEADS REBUILT | eBay

Then there's the cheaper route of just pulling used heads off a junkyard or something like that.. Just trying to explroe my options and figure something out. Hoping the bottom end is in tact and there's no hydrolock or anything bad cause i have taken the truck through a few mud puddles before.

Before this i was experiencing bad MPG, like 15 mpg, and just figured it was the fuel pump or injectors giving out.

What do yall think? I'm going to keep this truck as a project car, but i think my days of dailying her are over for now..

Never heard of a "flattened valve" before, especially on a non-interference engine.... unless they're trying to tell you the valve is so worn that the profile has completely gone and they need re-cut/profiled - which I don't know if I exactly buy either, especially if they just did a leak down test.
If you hydrolocked you would be experiencing a whole bunch of problems, with no start and rod knock at that top of that list. So I wouldn't worry too much about that.
I wouldnt be surprised if its related to the valvetrain, but I'd get another opinion first. Really your options depend on how much you care to spend/can afford. I definitely wouldn't buy a pair from some dude off ebay though...

Edit: Are you lifted and running bigger tires, or still stock? If the former, 15mpg is a little low BUT still very typical and those would be the culprits behind it.

If you know a good shop to rebuild your heads I say do it. I payed 360 to have my friends shop freshen them up and put new valve stem seals.


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I wouldn't guess the heads right away. The valves are a mechanical, not a hydraulic set up. Being a mechanical set up, if somethings amiss, the issue would be a constant. It won't be comes and goes. There could be a heat thing, like a hang up valve guide that tightens as the guides heats up. You know when that happens cause a very pronounced ticking.

I would try the coil or fuel injector first before guessing the heads. Unless you did a compression test? A different coil of fuel injector can't fix low compression.
You could try switching coils around to see if the misfires follow. You could ohm the injector to see if it's in specs. You can also try bg44k to clean up the injectors.

If your going to go the used head route, I would still have a shop go through it to make sure everything is good with it before install. Or take the gamble of redoing initial install cause of a bad used head.

what @HiLife said, it would be "constant" if it were a "smashed valve" (which the makes no since to me being said in the 1st place, if anything maybe a cracked head (but not being constant probably not.

I'd take it to another shop, do not tell them anything the other shop said, and c what they say...

There is still something going on with cylinder 3. The P code and the leak down.

Either way someone is going to have to pull that head. Then it will probably be obvious since that cylinder failed a leak down.


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Assuming they did the leak down correctly... There's no harm in getting another opinion. I've seen to many times when good meaning "mechanics" assume "blank" is the problem when its much cheaper/simple fix... and I'm taking about "u need a new engine" when its nothing to do with the long block but an accessory.

I not a fan of just jumping to removing the heads before all other variables r removed from the equation.

@VogRunner , did they tell u where the air was leaking into? crankcase, exhaust, cooling system, etc? That info is extremely helpful to narrows down shit... How many miles on the vehicle would also be helpful info.

Leaking head gasket?

He had cylinder 3 missfire code and the leak down detected a problem with the same cylinder.

But I get it. If it’s not too expensive to get another competent shop to look at it for piece of mind.


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What is a smashed or flattened valve? Like Devbot, I never heard of that term also.
And I never mentioned that term on my post.
@Devbot , wonder if the shop term of a "flattened valve" is actually a receded valve seat? That ressession could take up the valve lash, making valve tight. Hanging up the valve and burning it.
Then again, I don't see too many Toyota with weak valve seats prone to reversion issues.

My bad i probably didn't phrase the actual problem right. Not sure the terminology, first time this has happened to me. I've also been super busy with work and so my correspondence with the shop is minimal. My dad has a garage where we could pull the heads, but i can't really take time off work to work on it with his guidance (he's a mechanic). then we could take the heads to the machine shop, but i just really don't have time to do all of this right now, i have to have someone else do it for me.

So i'm considering taking out a loan to cover it because i love this car and it's been my transportation for only like 2 years now. Yeah so all i know is, he flow tested the fuel injectors, they were fine, and the compression test and leak down test showed a problem with cylinder 3... goes along with the code that popped up Gonna have to call them tomorrow to clarify what exactly it is, but they think for sure it's a problem with the valve train and they're gonna get my heads pulled and rebuilt. Hopefully there are no cracks or blown head gaskets, but obviously when you pull the heads you replace the gasket anyway... I'm fairly certain the bottom end is okay because of how bulletproof these are known to be... Fingers crossed

Again sorry if my lack of knowledge is frustrating, been working long hours and this isn't my area of expertise... yet :\

I was referring too ur comment that issue would be "constant". Valves and valve seat r cut to specific angles to help with sealing and air flow. The term flattened valves refers to when those angles r removed or flattened out by the constant smashing into each other, the OEM 5vz wouldn't be seeing much of this unless it a super high mile engine. This is seen more in high rev engines that have very high seat pressures from valve springs that require high forces to move up and down. This increase in pressure is used to stop valve float but the con is the increased pressure ware out the valves, valve seats, guides, and camshafts... to say it puts more ware on a valve train.

It would help if they said it was an intake valve or exhaust valves. The intake valves rarely ever go bad, they just tend to open up too much over time. The exhaust valves are a whole other story! I have seen them crack, chip, wear and do all sorts of crazy stuff in these 5VZ's with high mileage. If it was the exhaust valve no need to replace the whole head, you'll just pull bank 1 cylinder head and sent it to a machine shop for a valve job which will include pressure testing the head, milling it, replacing the valves and seals and shimming it to spec with the camshafts. That should cost much less than the $1299 + tax and shipping from those Ebay heads, more like half that amount. You don't need to replace both only have one rebuilt by a competent shop. Where in CA are you located? I'm in Citrus Heights near Sacramento if that helps at all and can recommend a shop or even take a look at it. I don't have a leak down tester any more though unless there's a place to rent one.

Labor will be expensive if you have a shop do it. You'll pay much more in labor than you will in parts.

@infamousRNR and I just replaced heads on his 2002. We got OEM remanufactured heads from Yota1 Performance. We're going to have a 7 Part video series coming out soon documenting the whole job.

We thought when we embarked on this job that maybe we could get away with just replacing the head with the bad cylinder. When we brought the heads to Yota1 to be vacuum tested, pressure tested and resurfaced, the suspect head failed the pressure test. There was a crack between the valves on the #3 cylinder that extended into a coolant jacket. Game over. The driver side head also had detonation cracks galore but it was still a technically sound head. But, the advice we got is no way do you want to put that driver side head back on the engine. The cracks don't stop growing. Eventually there will be an issue requiring the head to be removed.

So, I'm now of the opinion, if you have one head with a fatal issue, your other head is probably going to have some minor issues that will eventually become a fatal issue as well.

How many miles on the engjne? Was the valves adjusted between 250 to 300k?

Just curious if the exhaust valves not being adjusted has anything to do with the Tim Sean's head project. As I suspecting the exhaust valves being too tight caused this?

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