Thaik

Hi everyone,
I'm having this problem: My car seems to lose power as the car warms up, especially in the low rpm (below 4k rpm). Not only it loses power, but the engine seems more noisy, the engine seems to work harder as I depress the pedal further down. I can feel slight vibration in the gas pedal. When that happens, the car feels heavy, like the engine isn't powerful enough for the car. After going past 4k, the car seems to have power, but because the engine isn't working smoothly, and vibrates, but not that much, I can't stand it so I shift before going past 4k rpm (most of the time around 3k rpm).

It seems I can also hear valve noises, but not that much, it's more like the engine is noisier, and there's valve noise on top of that. I hear other civics engine, and have driven other Civics of the same generation, and the engine is much more quiet and smoother, which is what I like about Civics.

As I said, losing power when it's warm, it's worse when it's really hot (after driving for a long period of time), the valve noise is much more pronounced, there's some kind of tapping/knocking, and slight clicking that I can hear echoing against the walls of the roads. However, when it's cold, I don't hear any valve noise, the car isn't as smooth as others civic, but it's much better, the torque is there, power isn't that great, but it's a whole lot better than when it's hot. Unfortunately, that doesn't last very long, as soon as the car warms a little, I can feel that the engine is losing power, I have to depress the pedal more much in order the accelerate as fast, even there, it seems the car takes much more time to accelerate to a certain speed.

Here's what have been done on the car since I bought it few month ago:
-Engine oil changed with 5W-20 (like recommended)
-Transmission fluid changed
-Clutch fluid replaced
-Air filter replaced
-Spark plugs replaced
-Cracked manifold replaced (problem still there before)
-Valve adjustment done (problem still there, not worse, it's the same)

Well, pretty much all the basic maintenance related to the engine and transmission has been done, just in case. I did a compression test, I got great results around 200 to 210 PSI, that was a dry test, didn't do the wet test yet.

So here's my problem, what have been bothering me for the few past month, it's kind of depressing since I have no idea what it could be, could it be the valve clearance that have not been adjusted correctly? I adjusted them to 0.008 inches for the intake and 0.010 for the exhaust, which is the middle. I notice I'm getting better fuel economy ever since, so I think I did a pretty good job... if I'm not wrong.

One last thing, the engine seems to lose even more power on humid and hot days, the worst is when it's heavy raining.

Any input, feedback on this might be appreciated.

There might be some grammar or syntactical mistakes. Sorry in advance, English is my third language .

Thanks

MelJ

Although you didn't list it, was there a check engine light at all?

lazlong

Definitely scan it for codes.

Sounds like a restricted exhaust, which usually means a bad catalytic converter.

Thaik

Nope, there isn't any check engine at all.
I don't believe it is the catalytic converter since I replaced the exhaust manifold which is built in the exhaust manifold itself.
My car is a DX-SE(Special Edition).

Hmm, my car doesn't run THAT bad, from an average person point of view, the car runs ok, it's totally normal, but for me, someone who knows a bit more about cars, like pretty much everyone here, I know the engine isn't at its best.

Also, I'd like to precise that the knocking/tapping only occurs around 2k-3k rpm, a light tapping, especially when accelerating slowly and when maintaning the rpm around that range. That occurs and is most noticeable when the engine is really hot (optimal operating temperature).

Any more feedback/input would be appreciated.