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Hi All,
My 04 EX accelerates fine at low speed and idles very smooth. But it doesn't seem to have much power at >50mph. When I am on the highway with a small incline, it can't keep at 70mph speed. The engine revolves past 4000 rpm but it still can't keep the speed at 70mph. It used to be at 3000 rpm at that small hill. Is it a problem with my fuel pump, fuel injectors, transmission? I replaced spark plugs with the NGK specified in the user manual, ignition coils from Napa but it didn't make a difference. There is no OBDII codes.

There is a small oil leak at #2 spark plug well(If #1 is at the timing belt side). Does it cause the problem?

Thanks.

 
Rep Power: 211

Shouldn't be the cause of the power issue. The oil inside the well is most likely due to worn valve cover (spark plug well) O-rings. As far as the power loss..at what mileage was the last valves adjustment performed? Also, a compression test and/or leak-down test may be in order. Another thing to check is mechanical timing (cam/crank) as the timing belt may have skipped a tooth?

 
Rep Power: 518

check for exhaust restriction,
check for air intake restriction

 
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Thank you both for your suggestions. Glad to know the small oil leak from the spark plug well probably isn't something to worry about. I ordered spark plug oil seals I guess I can put it aside and try something else. My mechanic did the timing belt, water pump, head gasket, etc, in April with all the parts I bought from a Honda dealer. I don't know if he adjusted the valve. I will try a compression test.

As for the timing belt skipping a tooth, I thought I read the problem only shows up at high RPM? That seems to be my problem. At low RPM, my Civic doesn't seem to have any problem. It can keep up with traffic at a stop light and seems to have plenty of power.

For exhaust and air intake restrictions, it still has the original CAT I guess it's likely a problem. I just changed the air filter. I will check if anything in the air duct that blocks it or if the TB has problem fully open.

Thanks again.

 
Rep Power: 0

Update:

A transmission oil change fixed the problem. I will have 2 more oil changes in the coming weeks. I got 3 qts of DW-1 from the dealer here.
Civic OM says to change it every 90k miles. It was way overdue. It hasn't been changed for 150k miles lol. Thanks Ezone and Puffinblunts for your help. I should have mentioned on the long overdue transmission oil change since you guys can only help based on what we tell you. I didn't know it's important to change the transmission oil, though I change engine oil regularly.

 
Rep Power: 211

Good to hear you got it sorted out and thanks for updating so others may use this as a reference in the future.