Stumped... Cylinder misfire

[HiSpec]

My RSX Type-S currently showing P0304 (cylinder 4 misfire) and P0300 (random cylinder misfire). I've already changed new plugs and swapped coils but the code keeps coming back for P0304. The compression test came back even across all cylinders but a bit low at 150, so that rules out bent valves.

When I did the plugs, the valve cover gasket was also replaced.

Also, once a while P0302 (cylinder 2 misfire) codes appears but it shows up only once every 5 MIL reset.

Where should I look next if it's not bent valve being compression is even across all cylinders?

Thanks

[roll_over]

did you try swapping fuel injectors to see if it follows that injector?

[revelations]

So this came on suddenly and without you doing anything to it? (Eg driving through a giant rain puddle)

Standard process would be to rule out ELECTRICAL problems first, NOT mechanical.

[HiSpec]

Originally posted by roll_over
did you try swapping fuel injectors to see if it follows that injector?

Will consider as my next step

Originally posted by revelations
So this came on suddenly and without you doing anything to it? (Eg driving through a giant rain puddle)

Standard process would be to rule out ELECTRICAL problems first, NOT mechanical.

I drove through a small puddle (ankle deep) a month ago. Car did stall and started up right after. So don't believe it hydrolocked. The car drove exactly like how it was before the incident. The CEL suddenly few weeks after the puddle incident. Don't believe it is related to the puddle incident.

There's a slightly vibration on the motor and you can hear the faint misfire. The car does not feel like it has lost any power.

[cancer man]

I'd like to help you but first put on a vacuum gauge and watch the needle and report back.

Do the test at idle and at 3000 rpm. you might have a broken valve spring.

[RickDaTuner]

Originally posted by HiSpec



I drove through a small puddle (ankle deep) a month ago. Car did stall and started up right after. So don't believe it hydrolocked. The car drove exactly like how it was before the incident. The CEL suddenly few weeks after the puddle incident. Don't believe it is related to the puddle incident.

There's a slightly vibration on the motor and you can hear the faint misfire. The car does not feel like it has lost any power.

You may have ingested just enough water to bend a connecting rod slightly.

Compression tests, while use full, are not definitive, they only tell you a part of the story.

A cylinder leak down test would be helpful.

I would also recommend a data logger program like C-recorder, then watch the AFRs if they go lean when the missfire is occurring, then its an injector fault, if they go rich, then its a ignition fault. if the missfire is logged, and there is no dramatic change to the AFR, then you have a mechanical fault, where one cylinder is not contributing fully.

[HiSpec]

Originally posted by RickDaTuner


You may have ingested just enough water to bend a connecting rod slightly.

Compression tests, while use full, are not definitive, they only tell you a part of the story.

A cylinder leak down test would be helpful.

I would also recommend a data logger program like C-recorder, then watch the AFRs if they go lean when the missfire is occurring, then its an injector fault, if they go rich, then its a ignition fault. if the missfire is logged, and there is no dramatic change to the AFR, then you have a mechanical fault, where one cylinder is not contributing fully.

C-recorder... is this what you are referring to??

http://www.crecorder.com/website/ind...method=welcome

[reijo]

Plug wires?

[sr20s14zenki]

K20 use a coil on plug setup. But could be a plug boot.

[Kloubek]

The two suggestions I had have already been made.

1) Swap a wire if it will reach, and if that doesn't help,
2) Swap the injectors.

I'm 80% sure you'll find the issue. If not, it sounds like something internal.

[HiSpec]

Originally posted by reijo
Plug wires?

Originally posted by sr20s14zenki
K20 use a coil on plug setup. But could be a plug boot.

Originally posted by Kloubek
The two suggestions I had have already been made.

1) Swap a wire if it will reach, and if that doesn't help,
2) Swap the injectors.

I'm 80% sure you'll find the issue. If not, it sounds like something internal.

I swapped injectors and see where it takes me.

Thank you for all the suggestions so far.

[Kloubek]

Do the wires first if you can. Far easier.

[s_havinga]

I had the same issue in the jeep last year, it ended up being a broken valve spring. Hopefully not the situation here but keep it in mind.