P0304: Could it be a fuel injector?

DCB

DCB

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I am getting a P0304 code CYLINDER #4 MISFIRE Misfire detected in cylinder #4.

I know it could be a couple of things.

I have new plugs, coil packs and such. So I am guessing it's an injector problem. A couple of questions.


1) How can I know for sure that’s the issue?
2) Should I just change the one #4 or all of them?
3) Are rebuilt injectors ok to use?

Thanks
 
This caused my cyl #4 misfire, the fuel injector pigtail was shorting between the two wires where they enter the plastic connector..
20181222_080213.jpg


Misfires can be hard to troubleshoot. I have heard they are usually electrical as opposed to fuel related.

You can hear if the fuel injector is working by using a long handle screwdriver or mechanics stethoscope, touch one end to the FI and listen, you can easily hear if it is working.
 
Exactly what brand and model # spark plugs were installed? Some spark plugs some guide books recommend can cause a bad idle and misfires.
 
DCB said:
What about rebuilt factory injectors?
Click to expand...
I personally have never had to replace a injector in any vehicle that I have owned.
I have driven many of my cars well over 200k miles.
So i can't tell you what it good or not.
I was just giving you a chance to check to make sure you really need them. To many times on this and truck forums i have read "changed all injectors still have missfire"

Do not take this as they are not the problem. But just advise to test them first.
 
X2 I would swap the #4 injector w another injector.
If it is a bad injector, they are not expensive. I would buy new.

I did this last week, swapped injectors looking for a misfire.

That's what I would do next, that's your next step. Swap injectors and go from there.
 
So one thing that has been happening.
The check engine light will go off then come back on same code.
It went off again today...runs great. I did put in 3 bottles of Techron in it (2 different tanks). I have read that is really the only one to use.

Thanks
 
@DCB
Are you getting that code from the odometer or a hand held obd2 scanner?
And is it a P0304 code only?
And is it a 'random' misfire? , a random misfire should be noted in a hand held reader.
And is it a 'pending' engine code?
 
Usually if you have an injector fault for cyl#4 you would get a p0204. So at the very least the pcm isnt seeing an issue on the electrical side. However if you have access to a noid light set which you can grab at harbor freight for cheap it will atleast show you that the pcm is providing ground for the injector as the led with light up.
 
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My '05 TJ (4.0 liter, 90k miles) recently had the following symptoms: 1) a rough idle, 2) sporadic clicking noises near the front of the engine bay, and 3) fine power on start up, but after warm-up and going into closed mode, power would drop and sputter under load. All three symptoms persisted after flushing all 6 injectors, and replacing all 6 plugs, coil pack, TPS, cam position sensor, and all 4 O2 sensors.

I thought they were all unrelated issues, and I lived with it like that for a few weeks, waiting for the inevitable CEL. It finally threw a P0302 (#2 cylinder misfire) code so I took it to my local mechanic that I really trust.

Turns out, a wire connection to the #2 fuel injector had burned through, so he replaced the injector and wrapped up the other wires. He also had to replace all 6 of the new plugs which were now carbon-fouled (I had just changed them about 500 miles ago). With the new injector and plugs, all of the above symptoms (and the CEL) went away.

Just adding my experience here to hopefully help anyone looking to troubleshoot their 4.0 liter TJ.
 
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