PO304 errors keep coming back every 2 weeks after replacing plugs and coil

Bought this 2011 Tacoma for my son with 202,115 miles. It has been a great truck but on July 18th, he got the PO304 error and check engine light and several other warning lights came on. We took it to our mechanic and they replaced the spark plug for cylinder 4 and replaced the coil pack. The truck ran great for a little over 2 weeks and same error popped again with all the same error codes etc. Took it back to the same mechanic and they seemed to think maybe it was a bad part so they replaced the plug and coil pack and it has run great until it happened again yesterday with the same code. The problem now is my son is down at college with the truck and not here where we can take it to the mechanic. It seems odd the truck runs fine for about 2 weeks or so then it come back up after the replacement of plug and coil pack.

I am not a mechanic in any form but my question for the group is what could be causing this issue. I have read it could be a head gasket but like I said no issues for 2 weeks or more after the 2 things are replaced and the truck is not overheating or having any issues. Any help would be greatly appreciated as to why this possibly keeps coming up ever 2 weeks.
Thanks,
John

 

Update from last post took it to Firestone since it is next to college campus they saw the code ran it on their computer and cleared it running the car again with no issues running fine. I am sure just for another 2-3 weeks as has been the pattern.

 

Maybe a loose connection at the coil? Try packing the female connector with dielectric grease to hopefully stabilize the connection. If it comes back replace the connector.

 

Does it run poorly for a few seconds on cold startup? Then smooth out?

 

Hello -

Intermittent and slow-to-reappear trouble codes can be extremely difficult to trouble shoot. Even for the best of mechanics. So please be advised of this.

What other trouble codes were there? You mentioned "several other warning lights". So I'm wondering if there is anything else that would be helpful to understand.

My comments and suggestions:
-------------------------------------
1) The #4 coil and spark plug should have been replaced with OEM quality components. Preferably from the dealership parts counter. If your mechanic used lesser quality parts from the NAPA truck that runs all over town delivering stuff from shop to shop, then that could still be a lingering problem. Remember - any component or sensor that has to do with fuel injection, timing, spark, engine control, and the like *must* be a genuine Toyota OEM or equivalent replacement. Denso or NGK. Nothing less.

2) I have a sneaking suspicion *why* it is taking what seems to be so unusually long between when the CEL trips again. And I believe it may have something to do with your son's drive cycles. FYI - certain trouble codes - especially misfires and codes related to emissions - usually take a complete "drive cycle" to complete. That can be as long as 20-30 mins and may require the vehicle to be at other certain operating conditions, like full engine temp. And even crazy things like the gas tank to be between 1/4 & 3/4 full. No kidding.

For example, my youngest is now a freshman at LSU. We just dropped him off maybe two weeks ago. He's living on campus and can walk everywhere. He's on a meal plan. I talked to him earlier today and coincidentally I asked him if his car was OK. Like parked in a good, well-lit, parking lot. Parking pass is visible? Etc... I asked him if he'd even driven it and he said, I'm not kidding, "Not really. I went to WalMart the other day with my roommate to get some stuff, but that's been it."

And that right there might be one of your issues. A ~5 mile round trip to WalMart is not enough to complete a "drive cycle" for the engine computer to set (reset) a check engine light and store a trouble codes. So keep that in mind. Many mechanics do not ask enough questions of their customer or consider this type of scenario. They go straight to plugging in a scan tool and don't even bother with a proper road test.

3) Under no circumstances should you "guess" at your problem and just randomly replace parts. This is a terrible approach and you will waste money and time and possibly make your situation even more difficult to troubleshoot.

4) At 200,000+ miles and ~15 years old, the reality and my experience is that you have a minor mechanical issue. Probably a very small cylinder head gasket leak. Like a pinhole. That isn't causing noticeable coolant loss. But one that causes enough coolant to dribble into the #4 cylinder and cause an occasional misfire. This condition can be diagnosed by:
* examining the spark plug for being wet
* running a boroscope camera inside the spark plug hole --> a cylinder with coolant dripping into it will appear shiny and steam-cleaned as opposed to ordinary combustion residue.
* pressure testing or "block" testing your coolant system

5) Last but not least, it is slightly possible you have an electrical issue. Like a chaffed wire to the #4 coil that has a pinhole in the outer sheathing and is occasionally touching a metal surface and causing a short like when the chassis flexes when you go over a driveway. Very very very slight chance you have a failing engine computer that is not correctly commanding the #4 cylinder to fire on time. This is a *last resort* diagnosis and your mechanic darn well better explain his rationale for this before you send it off for repair.

HTH

 

Rob the coil has been replaced 2 times now
John

 

When the warning light appears it runs fine. I know one of the last times he started it and it was running rough and idling badly on the way to the mechanic. When the mechanic started it a day later said it was running fine.
John

 

Andy I looked back at the picture my son sent me and the check engine light was on as well as the VSC light. To be honest I am unsure what the shop used to on the replacement plug if it was a OEM or Denso or NGK. He just started back to school Friday so the truck has been driven a lot for more than 30 minutes so no real short drives. Friday we drove it to his campus and that is an about a 1 hour and 15 minute drive with no issues. The mechanic did road test the vehicle before and after and let it run for like 30 minutes with no issues the previous 2 times. Very baffling why this just came up out the blue and keeps occurring. Thanks for everyone's input.
John

 

I was referring to the factory wiring harness connector. Sorry I should have said male connector. Maybe the locking clip broke?

 

Update so he turned the truck on today after driving it 2 miles Sunday ran fine. Turned it on today and ran fine for 1 minute then engine light came on flashing and VSC light came on and it was running rough. At a total loss as to why it is happening usually does not go off again for another 2 weeks or more.

 

UPDATE: So error happened again check engine light was blinking, idling rough and VSC had truck towed to a Toyota dealer and they came back with a head gasket replacement. To replace the head gasket on both sides $4,400.

 

Find a good independent mechanic! I wouldn't be surprised if that number gets cut in half. At 200k, if you want to keep the truck, have them inspect the timing gear while it's open and replace as needed with OEM. The additional is minimal when you're already talking about thousands in labor. At 270k+ well maintained miles, my timing gear was in spec but definitely worn when the face was open to reseal the timing cover - https://www.tacomaworld.com/threads/1gr-fe-timing-rebuild-wear-analysis.835938/#post-29941550

Also, a minor detail just for future you to remember - the VSC light comes on any time the CEL comes on in these trucks. VSC has throttle control, so when a CEL is set, Toyota turns off VSC.

 

Can you post up the written quote from the dealership?

They should have presented it to you on a velvet pillow for that amount. With a couple of Excedrin underneath. $4400 is indeed a lot, but what does it include? Detailed info is extremely important here. This cost estimate, in terms of being reasonable, depends entirely on what is included (assumed).

This is time-consuming, technically tedious, and challenging work that requires a pro level of experience and tools. Parts and labor will add up quick. Keep reading.

Block out or blur the name the dealership info if you wish.
---------------------------------------
One would *hope* the quote from the dealership includes 'remanufactured' or even new cylinder heads. My experience is that very few dealers or independent shops anymore like to take the time to disassemble, clean, inspect, perform any type of machine work, and then put them both altogether again with new valves and springs and stuff. I think this is a valid assumption.

While it is possible to send a pair of cylinder heads out to a machine shop for such work, I no longer generally recommend it. Unless you know one terrific nearby machine shop and you are feeding it a steady diet of work, it takes too long and isn't cost effective. So, I would personally recommend and use on my own truck a quality pair of remain heads. Or whatever Toyota is sourcing. Any reputable shop should advise you of the same IMHO.

>>>> Caveat
You can take a conditional approach with your cylinder heads. Such as in the scenario (unlikely) they still look like new. And you or the mechanic(s) were able to identify the exact spot of the head gasket leak(s) and can reasonably assure you that a "head gasket slap job" will be a solution that lasts without issues recurring prematurely. As a shop owner, I would discourage you from that approach. It is just wishful thinking.

Not taking advantage of you, but by now I would have figured out this is your son's truck that needs to last him through 4+ yrs of college. You want your son to have a reliable vehicle. Because no matter how old they get, they're still your and his Mom's baby. You get the point. Perspective matters. Diagnose, educate, inform, discuss, provide reasonable win-win options. Blah blah blah. But we would have to have a difficult conversation about warranty conditions if you insisted on this "head gasket slap" approach as a customer at my shop. You can reasonably expect the same from any shop that has a reputation. A dealership will probably disallow such an approach because of their reputation and inability to provide you assurance of the work. Fair enough.
-----------
One would also *hope* that quote includes a complete new timing kit and accessories. Maybe / maybe not from the dealer. Timing chain, tensioners, guides, gaskets, any sensors that make sense to replace at the same time. Serpentine belt, spark plugs, oil & coolant fluids, and a water pump for the incremental cost. You would be penny wise and pound foolish to not consider this approach.
---------------------
Again, you can take a conditional approach with the timing set. You are way more likely to be able to decline this service due to cost than above. But the same concepts apply. Do it right the first time.
-------------
Given all of this, my approximate cost breakdown would be something like this (if I were an independent shop owner):

* 16 hrs of quoted labor --> plus or minus --> maybe 20 hrs if in my estimation I'm going to be fighting corroded bolts and brittle wiring harness connectors on a 200k truck
I would need to see the truck and poke around for 15 mins or so to narrow it down

>>>>> This labor would include: complete and necessary disassembly of the top end of the engine down to the cylinder heads, front timing set cover removal, and all associated labor to repair / replace the failed cylinder head gasket(s) and cylinder heads and replace the entire time set --> soup to nuts.

I would explain this outcome should essentially result in a complete "top end / front end engine re-build". You could easily expect another 50k miles if done correctly and subsequently maintained with regular oil changes. This is the goal. Get your kid through college where he can then buy his own truck. I would warranty this work, if awarded, for 6-12 months. Again, I need to see your truck first. And I get the first lick at if you have a problem.

Anyway:
20 hrs of labor (2-3 days) * $100 per hr labor rate = $2000 (discount applied on hourly rate for the size of the job)
Reman cylinder heads = $1000 inc shipping (these are not cheap as the supply begins to dwindle for your generation Tacoma, $500 each)
Timing chain set = $300 inc shipping
Oil, oil filter, spark plugs, belt, water pump, coolant, thermostat, etc... = $500 minimum

That's $3800 right there. That's my cost you you in my shop where I can have it from a M-F. No unforeseeable circumstances. I'm going to tell you that you should plan on a 10% contingency in parts that break when I touch them, another $400, but I will itemize everything to the hose clamp and I will keep you informed the entire way.

THIS IS NOT CHEAP WORK IF DONE CORRECTLY. I'm curious if the dealership quote includes a timing chain set.

Shop around. Call around. GET DETAILED QUOTES. UNDERSTAND YOUR OPTIONS.
----------
Last but not least, there is a very very valid approach you can take. As an engineer who worked in the oil & gas industry for a Big Oil company that was maniacal about predictive, preventative, and corrective maintenance - there is still an approach you can take that is known as RTF. Run To Failure.

An RTF approach usually depends on several criteria. Do you have a back up? Can you or the missus yank a summer Jeep outta your storage unit for a couple of weeks? And deliver it to your son? Does your financial situation allow you perhaps a more "peaceful" or "easier" option and you can just get him something else in the event of a catastrophic engine failure. You're not going to find very many good vehicles of any kind for $4400, but if you've got college already paid for in terms of financial planning, maybe that $12k a year from now is more appealing than a complex and complicated repair now.

All food for thought.
Apologies for the length and any typos.

HTH and best wishes!
Andy

 

Andy thanks for all the great info I am calling around some shops do not even do that work but I am talking to one that is close by and was receommended by another local shop. The dealership did not provide a quote break down it was just a text with pictures. Lame in my opinion for that amount but i know it is replacing both gaskets and as far as i am aware nothing else being replaced. I am trying to steer away from the dealership but one thing i heard was the antifreeze that has leaked into that cylinder causing more damage and eating away the metal in there. I do not know but thats what i was told today. There were no leaks we could see and it never over heated. Thanks again
John

 

thats a deal....
& THEY KNOW THEIR PRODUCT BETTER THAN ANYONE, THEY WONT CUT CORNERS REGARDLESS OF ALL THE DEALERSHIP SHIT TALKING THAT GOES ON HERE....

 

$4,400 sounds about right for both banks

I'd be wary of any shop that says they can do it for less than 4k

 

$4400 is in the ball park if it includes two new cylinder heads and a timing chain set and fluids and plugs. See my analysis above.

For two head gasket slaps? NO WAY, NO HOW.

My breakdown on that:

* One pair of Toyota cylinder head gaskets = $100
* Labor and profit = $4300

No way that is a 40 hour job to swap out two head gaskets.
------------
Indeed, there are local independent shops who will politely decline such work. Because it is technically complex and you need to be tooled up and have at least one experienced tech who can do it. This is not work for the faint of heart or first timer.

If all you do as a shop is brakes and AC system recharges and trival EVAP system leaks, then so be it. At last you're being honest by declining the work. Thanks!

There are however plenty of good independent shops that will do this work. They'll have a paved parking lot full of cars, a shop with more than one bay, lighting, techs in uniform, and a proper office.

BEST WISHES again!
Andy

 

It depends on labor rates, shops pretty much charge posted labor times which in this case is for 2wd 15.1 hrs for one side & 19.6 hrs for both, for 4wd it's 17.5 hrs for one side, 22 hrs for both according to Mitchell.

22 hrs x $100/hr = $2200
22 hrs x $150/hr = $3300
22 hrs x $200/hr = $4400

That's only labor, you have to add on all the required gaskets and other needed/"while your there" parts.
Price seems legit depending on where you are and the prevailing labor rates as they vary alot across the US, $90-$120 is pretty common for smaller shops around here but you get in the big city areas and it's $150+

 

After I took it to another shop they did not seem to think that was the issue as they looked at it with bore scope and there was some fluid in that cylinder but they suggested doing a fuel injector cleaner, using toyota approved spark plug and coil pack and see if it happened again. We just got it back late Wednesday and have driven it and so far so good but will ahve to wait and see.