The ongoing saga of P0304 on my 2000 3.4L

I still have a check engine light for P0304, cylinder four misfire. Truck runs rough, idles rough, accelerates poorly. The last time I took it on the highway to get into 5th gear, the check engine light flashed.

I think the culprit was bad gas but not sure.

Things Ive done:

--Replaced coils and spark plugs
--Switched coil wires to see if I had a bad wire
--Changed oil
--Fuel cleaner x2
--New fresh fuel I trust
--Replaced the MAF sensor

Today, I was able to get a long screwdriver on the fuel injectors. All seem to be firing the same so I no longer think that it is the fuel injectors.

The only thing I haven't tried (which I will today) is changing the fuel filter which could be the culprit.

Anything else I should try?

 

What's the compression on cyl4?

 

If you want to for sure rule out the injectors, swap them around and see if the misfire code follows. I know it’s not a super easy job to swap them, but it’s not that bad either. And it will tell you for sure if it’s the injectors.

 

Since the 5VZ is a waste spark system. I doubt its spark. But never hurts to do a visual check.

Just because the injectors sounds like its firing, doesn’t mean it is. Or that it is spraying correctly.

First thing I’d do is a compression check as the previous poster suggested.

 

Ok. Next up is fuel filter then compression and the fuel injectors. Sigh.

 

Fuel filter didnt fix it. onto compression.

 

How is your coolant level? If it’s low you could be leaking coolant into the cylinder. That was my issue 2 years ago.

 

I tested the compressor and cylinder 4 seems to be in line with the rest of them.

I will test the engine coolant level but I doubt that is the issue. But, I'll do that before I take it apart to test the injectors.

 

You can have good compression and still be leaking coolant. I was in the 180s on all 6 cylinders and was still losing coolant. Just check your resivor real quick it’s right there.

 

200

 

They make injector tester.
Relatively cheap for what it is.
I call it a buzz box tester.

Something like the one linked below.
But you'll need a fuel pressure gauge hooked up when you run the pulse.
You basically run the pulse on a known good injector (or all) injectors and see if one drops less or more pressure when testing.

allsun EM276 12V DIY Fuel Automotive Injector Tester and Cleaner with 2 Adapters and 4 Pulse Modes

https://www.amazon.com/allsun-Injec...tester+toyota+buz,automotive,119&sr=1-14&th=1

 

Coolant seems fine. Reservoir is mostly full. There is also no buildup on the oil cap nor any signs of overheating. Anything else to check?

 

The issue with the injectors isn't testing them so much as getting to them which is a pain and will take me several hours. If I'm gonna take everything apart, I might as well replace them.

 

I can understand that and see your point.

 

Last test I would recommend is a leak down

 

Don't think I saw a fuel pressure check.

Could always try reducing spark gap a little just to rule out a few things.

 

I will do a fuel pressure check. I've seen that most auto-part stores will do it. Doesn't make sense that it would only trigger a cylinder 4 misfire but, honestly, none of the fixes make that much sense.

I really think that it is a bad injector from everything that I've read. People whose issue sounds similar to mine have ended up swapping out the injectors.

 

Would changing the fuel pressure regulator be worth it ? Or testing it?

 

When you do the pressure check, the regulator will be half of what you're checking. The other thing that can cause low pressure is a dying pump or wiring.

 

THat makes sense but still confused why that would cause only one cylinder to misfire. But, I will check it tomorrow.