P0300 UPDATE

My thought is...

To me it doesn't matter how many miles are on some of the components, if you are going to be all the way in there to replace the water pump, you should swap out everything while your there. Timing belt, tensioner and bearings.

 

I’ve never replaced my crank bolt although I’ve read you should. Never had a problem though. If you do the water pump and timing belt spin the pulley on the tensioner and the pulley between the cams and if they make noise then I would replace them. Those bearings can last over 300K. When it comes to the tensioner it self I’ve reused them and I’ve replaced them. Worst case is if the tensioner goes bad you have to replace the timing belt again and do all the labor.

 

UPDATE:

We replaced the pump and timing belt successfully. Refilled with Toyota red and immediately made the 9 hour drive back to San Diego. It drove great! My startup misfire seemed to be gone for that day. It had strong starts and the code stayed away….. well, now it’s back. So that leads me to think that the blue devil gasket sealer either didn’t work or it was never needed in the first place. I have no smoke, I have great compression of 180-192, and my head block test was good. And from what I can tell, I’m not losing coolant anymore. I’ve been talking to a shop that shares the building with my work and he says that even a few drops of coolant in the combustion chamber can cause that misfire when starting. I would imagine though that it would at least misfire differently between warm and cold starts, but it’s really not that much different. If I had to explain it; it seems to turnover weak and slow, not a nice hard and fast turnover. Warm starts can usually take a few more clicks before it finally does turnover. Only times I noticed it had good strong starts was when all the injectors got replaced and when the pump and timing belt got replaced. Each only lasted a day. I’m planning on getting a camera stethoscope next to look inside the chamber after it’s been sitting all night to see if there’s actually coolant.

 

Did you ever resolve this issue? One of my spark plug threads failed and destroyed the plug and pack. Got that replaced and running well now but I believe that serious misfiring damaged my catalytic converter (now getting a P0420 code) and I am still getting the P0300 code. Curious if the P0300 could be from the P0420?

 

I ended up doing the head gasket job and I replaced both heads with refurbished ones in January. Misfire is gone, so it was either my head gasket or a cracked head. I never found out which. I know misfires that aren’t dealt with quickly can cause the p0420.
The p0300 is a random misfire not specific to any cylinder but that’s how mine started out, but then eventually became a 0306 and 0303. I would watch your coolant level like a hawk. Mine was slowly eating coolant.
In severe cases I’ve heard that a clogged cat can cause back pressure and then cause misfires in that way too. I have no experience in that, just something I heard or read somewhere.

 

Logan, I am having exactly the same codes and issue on a 3.4... thanks for posting

may I ask? would you ever throw a code after fully warmed or while driving? or only on startup?

 

This whole issue ended up being that coolant was leaking into the cylinders due to a bad head gasket or cracked cylinder head. I never officially confirmed which was the cause cus I got rid of the old heads as a core return for new ones.
Basically, coolant would seep into the cylinders when the truck was off because the coolant system isn’t circulating. So whenever I started it after it sat over night or for awhile, it had to burn out the coolant that had leaked into the cylinders before it ran smoothly, causing the misfire. Once it burns out the coolant after ~30 seconds it would run fine. This only occurred on cold starts for the most part.

 

Logans2001

thanks. I am not experiencing any difficulty starting or hesitation upon startup. Runs mint like a top always. Still getting a misfire code predictably after 5-10 min of driving. Still runs great after code triggers

 

Mostly po300 and will also trigger 303 306: coils, plugs wires new ngk

compression and leakdown tested fine

 

You never experienced a code after the car warmed?

 

Check your coolant level. Your leak could just be a lot worse than mine was and you’re losing coolant while you’re driving. Is there any white smoke coming from the exhaust? If you’re not losing coolant then it could be your spark plugs, wires, or coils.

 

no smoke ever, im starting to suspect something electrical or fuel related but still keeping your case in mind. all those compontents were replaced with ngk. i have never experienced heistation or rough idle on start up very weird

 

its probably the HG tho, due to the fact i rocked the heads when my fan bracket bearing popped and bearings, drive belts and cooling fan went flying
lemme fix my coolant has gone down but i noticed a leak so i gotta fix first ill be back thanks

 

how difficult was your head replacement? i smell more of a fuel smell on startup

 

also what company did you use for your new heads? would you still recommend, thanks you Logan

 

did you have to adjust valve clearance using shims on the new heads ?

 

This thread was all about my head gasket/cylinder head replacement job.https://www.tacomaworld.com/threads/was-trouble-installing-cams-now-restarting-hg-job.787833/ It’s not very difficult it’s just a lot of dismantling. I would try to reserve a good 3-4 days if it’s your first time, and that’s taking your time. I could probably do it in about 2 days if I had to again. And the link for where I bought the heads should be in that thread ^^. And the heads came fully built ready to bolt on to the block. I didn’t touch a thing. Valves, shims, cams, springs. Nothing.

 

Before you even consider doing a head gasket job you should absolutely make sure that you’ve ruled out everything else. I don’t think you’ve mentioned anything about your fuel injectors, fuel pump, fuel filter, etc. Those could be culprits too.

 

Thanks compression test was around 145 on all cylinders

leak down loss under 10% consecutive