P0304 Cylinder 4 Misfire...Injector???

Well I started her up this morning (also rained super hard last night...unusual), and she was running smooth until I hit the freeway about 10 minutes in and she was up to temp. Accelerated to 65 mph, and she started running super rough with the check engine light flashing until I brought her back down to 40-50 mph, at which point she smoothed out. Rough idling after that before I shut her off. Checked the codes, and came up with a P0304 cylinder 4 misfire. I'm going to work on her this weekend replacing and checking and replacing the spark plug wires (original factory wires) and checking and replacing all the spark plugs (replaced 10k/1yr ago), and cleaning the mass airflow sensor. I'm getting increasingly more suspicious that it may in fact be a fuel injector. I'm having some difficulty finding decent replacement injectors and am trying to avoid the 100% mark-up that the dealership seems to enjoy. Anyone replaced these and found a set of good reliable ones new or rebuilt? Also should I consider running sea foam or something similar to try cleaning out the injectors?

2001 Toyota Tacoma PreRunner 3.4L V6

Thanks for the input!

 

As a side note for anyone reading this, I found links in another thread to the

Denso Injectors: https://motorwestperformance.com/product/upgrade-for-23250-62040/#reviews
LCE Performance 5VZ Injectors: https://www.lceperformance.com/ProductDetails.asp?ProductCode=1062213&CartID=2

I'll keep updating. Wish me luck. This'll be a first time injectors job for me.

 

Don't be too keen on the issue being injector. P0304 can also relate to a cracked head or head gasket issue. I would do a compression test and leak down test before tearing into it. Just my opinion.....

 

Do some more trouble shooting this could be rings could be in the head valves or a crack

remember the code is the complete circuit anything that could cause a miss fire on that circuit

though inspecting the spark plug is first

move the coil pack see if the code moves with the coil pack

 

+1. Switch out the coil pack with another cylinder and see if the DTC P0304 remains. If it does remain then conduct a compression test on #4 Cylinder. If the compression is good then checkout the #4 Injector.

 

So I replaced the spark plugs and wires, no oil fouling or cracking, but the idle is now pretty rough and she’s backfiring, which make me not want to drive very far at all to throw a code (I swapped the cylinder #1 and #3 coils). The coils seem fine as well. Checked resistance on all and it was good. Frustratingly I have to take the manifold off to access the #4 injector, which I was hoping to be able to listen to. All the others are clicking away happily. Some engineer just thought it would be great to bury #4 under the manifold. I’m ordering gaskets for the manifold before I tear it down, and then compression and leak down for all. Not sure if I should just bite the bullet and order new injectors. She’s at 210k miles and the injectors are original, and I don’t think they’ve ever been serviced.

 

Also I should mention that prior to this becoming an issue, the fuel economy has been trash at around 16mpg no load.

 

I would do a compression or leak down test before pulling things more apart

 

Sounds good. I’ll have to either purchase the equipment or take it to a shop and have them test it. I would prefer to purchase the equipment, any recs on what’s reliable? Seems to be a hit or miss on gauge accuracy if ordering from harbor freight or another retailer.

 

X2

 

Try this:

https://www.northerntool.com/shop/tools/product_200581093_200581093

 

The part where you said it runs smooth until it hits temp is what is making me raise my eyebrow a little bit. It could be a failing electrical item which starts to overheat eventually, but it also could be a defect in the head gasket or something mechanically failing which is fine until things expand with the heat. As previously noted I would get a cylinder leakage test before I do anything else, possibly even a compression test, especially because it's an older engine with who knows how many miles are on it. High mileage engines are always suspect mechanically until their integrity is ruled out, but it should always be the first area of attack, as well as vacuum leaks being checked and ruled via smoke test.

Also, this is a given, but you should always make sure vital fluid levels are up to par and at level.

 

Another +1 on electrical, as mentioned. As a side note I had a similar code (can’t remember if 303 or 304). Turned out to be bad coil pack coupled with a way overdue fuel filter change.