P0304 MISFIRE ON CYLINDER 4

That's called "sticktoitivness". Great job! Thanks for sharing your adventure with us.

 

Well done. Sounds like you discovered that the EGR system may benefit from periodic cleaning...

 

very interesting. i just experienced this problem on my 2010 prius at 115,000. started and rapidly progressed until i had to tow it in to toyota. They covered it under emissions 15yr/150000 warranty.

Question is what caused this?? I'm losing about a qt of 0w20 every thousand miles, no smoke, no leaks
hopefully someone can answer me. my current guess is that the root cause is going to worsen and I'll end up needing a motor job

 

My first thought would be a spark plug oil fouling. If that's the case, then yes, you might have a more serious condition. I would pursue a solution before the drivetrain warranty expires.

 

To give pjksr02 credit, he did mention intake in his long list.

 

i have a question. Toyota installed a new intake manifold , gasket and EGR Pipe gasket for the same symptoms described above; P0304, body shake .... the engine now runs smooth but the mileage is still down at 41-42 MPG. Can any other components have been affected by the excessive oil ( the root cause problem) Eg, throttle body, MAF ?

 

The o2 sensors may have become a little contaminated with soot but the voltage range on them is relatively narrow. They could be affected to the point where they are boarder line without turning on the ECL. I would give it some time for the catalytic converter to burn off the contaminates. A good long drive at highway speeds may help improve the fuel mileage. Just give it some time.

 

hmm. i drive 110 miles per day (80% highway) 5 days per week. when i first got hte car back from the dealer the MPG was at 48-49 but quickly dropped back to 42ish

 

Hmmm, is right! ???at this point. Someone else may have suggestions.

 

Start with checking tire pressure.

 

Hi

I have 1 question for you (pardon my ignorance): During all this time, did you have any other DTC besides the misfire code P304? The reason for asking is that I have a prius 2005 with almost same symptoms. I have changed spark plugs, swapped coil 4 with 1, and the problem still stays at cylinders 3 and 4 (for me i have the dtc 0300, 0303 and 0304). So far engine side, I have only checked the compression and it came to around 104 PSI / cyl.

I also have a terrible noise whenever the prius is trying to charge the HV battery. It's sort of a clunking rattling noise. However regarding the noise, I believe I read in priuschat smth about coming from old worn out springs in the frywheel. My prius has 230000 km, so I believe that the missfires are causing hesitation in the driveline, thus creating the noise. However all this is speculation. If you or anybody else can point me to the next step in fixing my problem I'd be extremely grateful.

 

Nice!!!!

 

I would follow Catalinux's lead and check/have checked the EGR pipes in the intake. Also, the noise you are encountering May be the flywheel dampener reacting to the lost of torque on the misfiring cylinder. The dampener springs are probably unloading during the misfire.

 

If anything goes wrong on my car, I want someone like Catalinux to work on it. Someone who just doesn't give up until the real problem is fixed. Good job, man!

 

A little follow up on my problem with the Prius.

I live in Montreal Canada, and though the city is big there aren't that many "intelligent" car repair shops that would take a prius in for repairs. The moment they figure out its a hybrid they all throw their hands up in the air and say "OMG IT'S A HYBRID" as if I've brought a vampire onto their shop. Needless to say nobody accepted to look at the car and its problem, so I was forced to bring it at a Toyota dealer.

They swapped 1 injector and 4 top injector seals. This cost me close to 800$ (canadian). It made the problem go away, only for a week or so, only to reappear again. Last I spoke to their manager he told me that one possible problem for this can be bad gas, and offered me a free bottle of gas-removal additive. That DID NOT help either.

Now the manager is of course in vacations and I really am left with a car whose catalytic converter temperature, at times runs in excess of 700 degrees c. I really don't know what to do anymore. Maybe Montreal is not suitable for Prii, maybe I'm approaching the problem from the wrong side. Whoever has any experience (either from Montreal) or with a similar problem, please either PM me, or let me know.

Thnx all for your help

P.S.: A friend of mine told me that I might have to look into the catalytic converter, because they too (as catalinux found out with the egr pipes) get clogged up with carbon build up.

 

I am posting my experience of my own issue:
I changed my spark plugs at 120,000 miles.

For the last 2,000 miles (125,000- 127,000) I have had the same symptoms.
1. Knocking at idle/low rpm
2. Knocking and shacking at high torque low speed
3. P0304 check engine light

I read this post which was the only real experience with a fix (other than people stating they used high octane fuel and techron) So I had a lot of confidence that the manifold was the cause ( especially with the tsb that toyota has released a revised manifold).

I tried fuel cleaners and high octane and ethanol treatment. 5 tanks of this and nothing

After 3 tanks I removed the intake manifold and soaked it in plastic cleaner then sprayed it out with a pressure washer. Lots of carbon came out, but it was not that dirty really. I will admit though I experienced the opposite of this mans experience. The number 4 piston is right next to the egr gas intake hole. So the number 4 and 3 holes were fairly clogged 4 much worse than 3. 1 and 2 egr ports were clean. I also cleaned the egr tube (which was pretty dirty).
This did not fix my problem.

So I tested the coils. No problems.

I decided to check the spark plugs ( toyota spark plugs (denso) )

I quickly found that the #4 spark plug looked like the tip was worn down compared to the others. I checked the gap of this one and the others. They were anywhere from .053- .065. With iridium plugs the advise is that you do not need to set the gap, because it is set at the factory. I read on denso website that the spark plugs should be .040 gap. They also said that if you need to set gap use pliers and do not touch the tip. They are basicly admitting they have poor quality control. I also checked the original plugs from the car that came with it from the factory. They were just as bad .055-.063.
I think anyone who thinks they have changed the plugs and that it is not the issue should check the gap, and set it if needed to .040.

The idea of not setting the gap is crazy! I have used NGK and Bosche on other cars (turbo sports cars) and never had a problem. Also I never checked the gap I just followed the general advise that it was not needed.

WHAT A CROCK!!!

Denso is a mainstream company with poor quality control.

I decided to replace these all with Bosche from autozone at $6.99 each. This was because they were the only iridium plugs in stock available in my town. They looked great on opening. Cleaner and better finish then the DENSO. Also they were all almost identical gap. .038.

I installed the plugs and WA LA. Problem solved. Now I will admit my #4 plug tip did look like it was chipped off at the top just a tiny bit compared to the others. I did not touch the tip before or during install (as I did not use a filler gauge to check these).

Reading DENSO website they also state that the iridium tips are very brittle and can chip easily.

CONCLUSION: DENSO plugs are trash. They have poor quality and are mass produced with low quality control. The BOSCHE plugs look to be of far better quality all around and the GAP proved that quality control is high.
CHECK YOUR GAP AND SET IT!!!! Just because they are set at the factory does not mean it was set correctly.

I personally believe that with a good strong spark the manifold will not be a problem. I know of many cars that flow fresh air and bypass the egr with no issues or block the EGR path completely with no fresh air. And the motor runs fine, no misfire.

I believe that this issue is caused by Original DENSO plugs installed by the manufacturer, and due to carbon build up and other things like poor fuel or worn or dirty parts the engine starts to misfire at higher mileage.

Many people have cleaned and replaced injectors and manifold with temporary results. CHECK YOUR GAP AND GET HIGH QUALITY PLUGS. IF YOU HAVE SOMEONE INSTALL YOUR PLUGS AT A SHOP ASK THEM TO CHECK AND SET YOUR PLUGS REGARDLESS OF THE IDEA THAT THEY ARE SET AT THE MANUFACTURER.
I hope this post helps the many others who are frustrated like I was!!

 

Prior to your replacing the spark plugs, were there any engine performance problems?
Immediately after replacing the spark plugs, were there any engine performance problems?

If there were no issues at that time, then it appears that the newly installed spark plug in cylinder 4 had something happen to it after 5K miles of usage?

I agree that it is necessary to verify the iridium spark plug gap before installing. The correct gap is 1.0 to 1.1 mm.

 

No issues before spark plug change. Maybe around 70,000 I noticed that the mpg had dropped, but I think that is because I stopped using the little tricks to improve mpg.
So no. No performance issues.

I agree that the #4 plug probably had an issue within the time I changed them to the time I had problems, being that the tip looked slightly different than the others. The gap was .065.

I did not spend the time to test it, but I would speculate that if the gap is too large you will misfire or have low spark as the check engine light lists.

With 8 plugs from toyota they were all set at .053-.065 (1.35 -1.65 mm). My guess is that people have no performance issues (with factory set gap being to large) until something else comes into play. I would assume if any other issues are there such as poor air fuel mixture (egr clogged, manifold clogged, fuel injector clogged, bad gas) then the problem would present itself.

When I cleaned my manifold it was not very dirty. I will admit the #4 egr port was almost closed. So the new manifold listed in the tsb sounds like a good idea to replace with, or clean it every 75-100k miles.

Most cars the egr can completely seal with carbon and then you get a check engine light for egr not a misfire. I strongly believe that factory toyota plugs are to blame (gap not set correctly).

I would love to hear from everyone who had this problem and find out what the plug gap was set to when they had issues start. And if toyota replaced the plugs or they did their self.

A strong spark will run a lean or rich engine. But low spark will cause misfire.

OH P.S.
Those having oil consumption issues should change their pcv valve. I think toyota calls it their ventilation valve (this service is not in the manual, but most cars replace every 30k or so). PCV valves are also a lot of times poor quality. Blow into the new valve and it should seal completely if it does not seal, return it and get another that does seal. Don't clean it the existing one, the spring can wear out and it may not open and close as effectively. They are only $6 from toyota new.

 

I gotta bump this thread because I just started experiencing the same problem. It started with a shuddering jerking motion from the engine vibrating the whole car (9.12.17) then the check engine light came on. After the CEL came on the shuddering vibrating went away?? Took it to autozone and came up with P0304 CYL 4 Misfire. Everyday driver (133K) and average about 800 miles a week. Bought the car 2 1/2 years ago with 50K so I doubt spark plugs were ever done. I'm going to attempt to change the plugs, clean out the EGR pipe. I pray that's all it is. Any input is definitely welcomed.

And side note, this sucks because I just changed out the Transmission fluid which came out black. I hope it's not going to pour on me :/