P0306 cylinder misfire

[Tmiron]

Yesterday my gas light came on and a few minutes later my engine started shuddering. I checked the code and it read p0306 (cylinder 6 misfire). I replaced the spark plug and cleared the code. The wire looked fine. Started it up and it didn't seem to shudder at idle but as soon as I started driving it came back and so did the code. I added a bottle of seafoam injector cleaner and drove about 10 miles, but it's still shuddering.

What's my next step? Order and replace injectors? Drive more to see if it cleans out? replace the other plugs and wires?

Thanks for the help

 

[brillo_76]

Yesterday my gas light came on and a few minutes later my engine started shuddering. I checked the code and it read p0306 (cylinder 6 misfire). I replaced the spark plug and cleared the code. The wire looked fine. Started it up and it didn't seem to shudder at idle but as soon as I started driving it came back and so did the code. I added a bottle of seafoam injector cleaner and drove about 10 miles, but it's still shuddering.

What's my next step? Order and replace injectors? Drive more to see if it cleans out? replace the other plugs and wires?

Thanks for the help

I would verify the coil and the plug wire are good. https://www.toyota-4runner.org/3rd-g...on-5vz-fe.html

The link has the testing to procedure to verify what is good and bad.


I am suspecting, that the injector maybe clogged. However, its best to rule out the spark plug, wires coil first. Just in case of the those components failed at the same time the gas light came on.

 

[MaineRunna]

I would probably do a compression test on cylinder 6 and listen to the fuel injectors with a mechanics stethoscope to see if they all make a good solid clicking noise while running. If the coil is bad it should run like total shit because it would be misfiring on two cylinders. If the wire is bad it would skip on one cylinder. If it has a dead miss at idle I would suspect a fuel injector or compression issue. If it misses under load I would suspect the wire.

 

[PoshSnoop]

Test the spark plug wires. I had a P304 awhile back, and one relatively fresh Bosch spark plug wire had gone bad. I ordered up a Genuine Toyota wire set, paid the price, and drove off into the sunset.

 

[Tmiron]

Update

I changed the fuel filter, cleared the code/ CEL and drove for about 15 minutes. The stumble seems better but not gone. It's intermittent now. I had my CEL light flash a few times at one point but then stopped. I checked the codes after 15minutes of driving and have a pending P0306 and P0300.

Should I keep driving? I don't want to make it worse, but it really seems like a fuel delivery issue, so my thought it that it should get better with a bit more driving....

 

[brillo_76]

So did you do anything the other members suggested? As changing the fuel filter wasn't suggested and you can see it did nothing to fix the issue. Its best to pinpoint the exact issue before you just throw parts at it hoping to solve the issue. Flashing CEL is misfire errors. Also we can't truely answer if its safe to keep driving to the exact issue is proven. Yes it could be a plugged injector and it also could be something else at this time.

 

[JohnMc]

Some random things to try:
1) "Shade tree" compression test. Pull the FI relay (it's on the panel under the hood) so it won't start, and then crank the motor and listen. Does the cranking slow over all 6 compressions pretty evenly? Or are there some 'easy' compressions mixed into the pattern? whir-whir-whir-whir is good, whir-whir-whee-whir-whir is bad. Obviously, far superior to pull all the plugs and do a real compression test with a gauge, but this is a quick and easy way to check for major compression issues

2) Move the coil. So far #6 seems to be the major source of problems, see if it follows the coil. Because they're different lengths, it can be a bit more of a PITA to move a plug wire to a different coil/c, but try that as well. If it stays stuck on #6, starting to point more firmly at an injector.

When an injector failed on mine it would cold start just fine, and even keep running on shorter trips on all 6 just fine, but warmer days and/or longer trips would bring on the misfire/CEL. With a slowly increasing frequency.

And try to avoid some of the cheap counterfeit knock-off Chinese junk injectors you'll find for sale. If the price on a set of 6 OEM BRAND NEW INJECTORS is too good to be true, it probably is. I bought a set of 6 on eBay, said to be new, unused, OEM Denso* injectors. * - First clue I missed, the OEM injectors are Aisin...). Received them in the mail, they were in plain clear plastic bags (no boxes because they BUY IN BULK, lol). But srsly, even looking at them up close they looked entirely 100% legitimate like the injectors I took off. Put them on... and they sucked. Uneven idling, slow cold starts, hot start issues (I'm assuming one was leaking down and flooding the engine). I yanked them back out and got the seller to accept them back for a 100% refund, and stuck a set of injectors I got from a 5VZ in the pick and pull. Which have been perfect. FWIW, after that truck had sat around in the insurance system and in the yard for who knows how long, 2 months or more?, when I cracked the fuel lines at the junkyard fuel sprayed out under pressure.

 

[FD7683]

I had symptoms like this mine being cylinder #5. There were days when it drove good for 5 mins then it would start missing. Most of the time the truck would miss on cold start but giving it heavy gas it would start firing again. Spark plug and coil checked out as good, it ended up being the fuel injector. I replaced all 6 with Motorwest Performace Denso fuel injectors and all is good. Yes, as said its not recommended to buy eBay "OEM refurbished" fuel injectors for cheap. If you do fuel injectors there are crush washers you need to buy from Toyota for the fuel injector rail.

 

[mtbtim]

It certainly sounds like a partially clogged fuel injector based off the circumstances that lead to the misfire. But, then again, debris at the bottom of the tank should be handled by the pre-filter on the fuel pump and secondly by the fuel filter between the tank and the engine.

To not throw parts at it, it would be smart to do a compression check of the cylinder first. And, you may as well check all 6 cylinders while you're at it.

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[B]If you find any of the cylinders have low compression, I'd follow it up with a leak down test to figure out where you are losing the compression.

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If the cylinder compression is all good, the next most affordable thing to do is replace the spark plugs and wires. You renewed the cylinder 6 spark plug, but I'd do the rest. How to effectively test spark plug wires, I don't know. They can produce intermittent problems of conductivity. Replacing the wires could be viewed as throwing parts at the problem, but wires are something everyone should replace at some point as general maintenance.

If the plugs and wires don't fix the issue, I would then next replace the injectors. Again, injectors can be tested by doing an Ohms resistance test, but how you determine if the injector is flowing optimally without special equipment, I don't know. I know there's DiY ways to clean them, but a DIYer can't really determine the flow, at least I don't think there's an easy and affordable way to do it. So, I would recommend replacing all 6 injectors, not just the affected cylinder. With flow matched injectors, your engine will run better. But, if money is tight, replace just the #6 injector and see if that fixes your problem. Motorwest in Performance in Southern California sells good injectors for a fair price. MotorWest Performance, Inc. | Home

I would not buy injectors from Ebay sellers. There's a lot of Chinese knock-off Denso & Aisin injectors and they are crap. I also wouldn't buy OEM injectors from Toyota. They are way too expensive.

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[MontanaYota]

Used this info to diagnose the same code on my 99 T4R. Had shuddering after hot restarts and after swapping spark plugs, coil packs, and cables without the misfire moving, determined it to be the injectors. Replaced all 6 with MotorWest performance injectors and misfire is gone and MPGs went up (from 17 to 21 mpg!) Also was able to clean intake and plenums at the same time so extra bonus.