P0304 code - misfire in cylinder #4
 

On the wife's '99 4Runner (3.4, 5 spd, 122K miles) I am getting a P0304 code. Ran fine yesterday, drove all over town with no problems. She drove to work this morning and said it was hesitating and vibrating, yet no CE light. On the drive home tonight, same symptoms, then the CE light came on.

When she got home I went to check it out. It definitely sounds like it is missing. Making a ffft, ffft, ffft sound from the exhaust. Pinging under load too. Went to AutoZone to pull the code. Came up with the P0304 and a message saying "The PCM has determined that a misfire has occured in cylinder #4."

First of all, #4 should be on middle driver side correct? What would you guys check first? The plugs and wires are about 2 year old Densos. The coils are probably original. I did the timing belt replacement at 118K, and cleaned the MAF recently too.

Thanks for any help.

Hodag

Swap coil packs/wires and see if the problem "moves."

After that do a compression test if the problem cylinder doesn't "move". Any smoke from the tailpipe? What does the oil look like?
My wifes 4Runner was doing the same thing yers is and I got a busted head gasket. What a joy to behold this holiday season!

Ryan

Oil looks good, no smoke from the tailpipe. Those are one of the first things I checked, being that I am a glass half empty kinda guy.

I guess I start with plugs, wires, and coilpack. Ill swap them around to see what happens.


Thanks, Hodag

You might want to read over here a well:

https://www.yotatech.com/forums/f2/p303-misfire-detected-100681/


And, starting at post 5, this thread hijack walked through a similar problem:

https://www.yotatech.com/forums/f2/smt6-open-closed-loop-fix-idea-100230/

Toyota had Head gasket recall for early 1996 3.4 L models (my 4Runner was one of them).
I would recommend contacting a dealer.

BTW how many miles in your wife’s 4Runner?

Unfortunately the dealer will just tell you that the service campaign for that is over. I believe it ended in October of 2004, but they might have put through a few at the end just past that date. I doubt you'll get Toyota to budge on that over 2 years later though.

Besides, the campaign on the 3.4 HG was an external flaw, or so the dealer told me when I had mine done...

Well, heres the story now. Just got in from changing plugs and wires. Number 4 plug was obviously the culprit. Very black and worn compared to the other 5 plugs. Went ahead and changed the wires too (I think they were original).

The truck runs fine now, no ffft, ffft, ffft, no shudder and hesitation. Autozone was closed so I havent cleared the code yet.

What would cause #4 plug to go bad? Faulty plug? Injector going bad? I guess at this point, Im just gonna drive it and wait to see if the problem arises again.

Thanks for the help.

Hodag

Pop the hood, open the fuse box that's on the driver's side, just in back of the battery. Find the fuse marked "EFI", pull it, wait a few seconds (some say a full minute or more), then plug it back in. That'll do two things, a) clear the dialog code (and thus the MIL), and b) reset the ECU which is a good thing 'cause while it was complaining about the misfire it made a mess of your timing.


hard to say... But a visual description of "Very black and worn" doesn't necessarily convey that the plug went bad, in fact it kinda' makes me think that the plug is showing a symptom of something else wrong. Can you post a pic? If not, then can you explain what you mean by "worn"?

And... you gapped the plugs to .040" before you put them in, right?

Could be that the plug had a cracked electrode or the ceramic was cracked when installed or perhaps the gap had gotten large enough to cause random misfires. If that was in fact the case, it wouldn't be the first time that a plug was responsible for a misfire.

Best you can do now is reset the ECU and drive it until it throws a code again.

Yeup, I know :) but it could also be... well, do I have to post "that pic" again? :)


True Dat!

Without being there it's all a guessing game anyway, right?! :laugh:

......"I can name that tune in XXX notes!"

Thanks for all the input guys. As always this forum has been a great help. I just used it as reference when I did the timing belt, cleaned the MAF, and throttle body. Luckily the 4Runner has been very reliable and I have been able to tackle everything myself. The 3.4 is a little more complicated than the 2F in my FJ60.

I reset the ECU this morning and drove about 15 miles so far with no problems. Seems to start better for sure, and all the other bad symptoms are gone.

Thanks again.

Hodag

160,000 miles on my wifes 96 4Runner. Already contacted the dealership. They said no recall. Not believing them I contacted Toyota corporate. Corporate said no recall on the engine.
My gasket looks like it had been replaced already and whoever did it put waaaay too much torque on the headbolts.
Good luck with your Runner friend.
Ryan

Are you saying that Toyota said a recall never existed, or the recall did not apply to your VIN?

This guy has a good video on at least changing spark plugs and coil pack to fix this code:

Nice on bringing back an 11 year old thread guy...