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Sadly my sons 2007 civic has a continuous misfire issue. Plugs, and coils have been replaced along with the upper oxygen sensor and a single fuel injector for cylinder 4. We just cleaned the EGC valve. Still reports a misfire on cylinder 4.
The check engine light comes on as soon as it is started. If we turn the car off and then start it again with the accelerator depressed (5000RPM) the issue temporarily goes away.
Anyone have a clue what to try now ?

 
Rep Power: 222

What codes come up?
What brand of parts did you use?
What was the condition of the old spark plugs?

 
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Thanks for responding
code P0304
oddly the 4th plug was looking the best (light grey) the other three were dark with soot.
NGK plugs, one coil from Lordco then the others from Amazon.
I don’t think it’s the coils tho because we can switch them around and the misfire stays at #4.
The 0xygen sensor is Bosch
The #4 fuel injector was done at Kal Tire
The EGV is a cheap China part cause we are running out of expendable cash right now

When the engine is cold, it misfires and will not rev up past 1800RPM. If the engine is turned off and then started again with the accelerator depressed the issue goes away

 
Rep Power: 222

Can't use Bosch, needs to be Denso/ntk

 
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Why would the code come up as a misfire on #4 instead of a faulty 02 sensor then ?

 
Rep Power: 229

Its either
-spark
-fuel
-or signal

Easy spark test:unplug 3 other coil packs (1,2,3). Leave 4 pluged in, but remove it from the head. Make sure the spark plug is in it. Crank the engine and watch for a white/blue spark. You will need to tie a wire around the plug threading and to a ground source.

if you have spark then there is an issue on the fuel end. If no spark then we look there.

check spark and report back.

 
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Ok !
cylinder #4 has spark

 
Rep Power: 229

So you know it is a fuel issue.

To clarify that the new injector is good, you can use an multimeter to measure resistance across its 2 wire plug. I cant remember but I think were looking for a hundred ohm range between 900-100. If you see infinite ohms, then the injector is bad.


You can listen to the injectors using a screwdriver, make sure when the vehicle is running that you can hear all injectors (excluding 4). Make sure you are low on the injector, near the rail, on metal. They should sound like a tick, tick,tick, tick, a bit faster paced than a ticking watch.

If #4 injector is firing at idle then we're looking at a bad/clogged injector at high rpm (so replace it), or the wrong brand injector which can fire with too much/too little fuel, or a compression issue.

if injector 4 is not firing we're looking at a signal issue or "injector pulse". Type "testing fuel injector" into youtube and you can find videos on the 3 tests (ground check, voltage check, resistance check).