Engine Misfire?

2008 HONDA ACCORD
165,000 MILES • 3.5L • V6 • 2WD • AUTOMATIC
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JGONZO2398
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So I have another cylinder 4 issue. I was driving to work yesterday and my check engine light started flashing, I got it scanned at an AutoZone and got a P0304 code, my engine was rough idling. The last time I did this was November 2024, same exact code, I replaced the spark plug and ignition coil, and the problem got fixed. When I got home yesterday and removed the spark plug, it was a bit burnt, I also swapped the coil with another one, but the problem would not go away. I just took it to my mechanic and he did a compression test on all the cylinders, they all had normal compression except for cylinder 4, it had none. He told me that he needed to replace the valves and the head gaskets along with the timing chain, he quoted me $1,800 for material and labor, what are your guys’ thoughts?
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Jun 17, 2025 at 6:27 PM
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STRAILER
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Yep, no compression will do it, yes $1,800.00 is not a bad price for the job. I would have it done. Try to ask him if he sees any reason the price might go up after it is apart?

A P0304 code - Cylinder 4 Misfire Detected

I know there can be, but it is best to start this way to help keep the repair under control. Let me know what happens please. Also, this guide can help as well:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please go over this guide and get back to us.
Jun 18, 2025 at 7:04 PM
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JGONZO2398
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He told me that there shouldn’t be any increase after the work is done. However, another detail I noticed on the way to his shop was that my brake pedal was a lot harder to push, and I also noticed a hissing noise coming from the brake fluid reservoir after I turn off the engine. For some reason, I completely forgot to check the fluid level, but now I am assuming I either have a leak or a bad brake booster.
Jun 18, 2025 at 9:31 PM
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STRAILER
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Yep, it does sound like the brake booster needs to be replaced as well. If you start a new thread, I can give instructions on how to change it out.
Jun 19, 2025 at 10:01 AM