Q: Loud knocking sound when engine is running

asked by on

I have a loud knocking sound coming from the engine when the car is running. There are no OBD codes pending or present. The sound is not present if I try to start the car with the fuel pump disconnected. I took the cylinder head off to find the cause and only found some carbon build up with a broken knock sensor. I replaced the knock sensor, cleaned the pistons, and the cylinder head. The valves looked fine they werent broken or bent that I could see. Then I put the head back on and I get the same sound. It's only when the engine is running and under combustion that it's present. I checked the timing and it's fine.

It started with with fluttering sound while driving at freeway speeds over the period of a week and then the engine just shut down. No bang, no loud noise just turned off like you would do with the key normally. No codes at the time either.

I have no idea what it could be except a bad rod or bearing. Naturally I hope it isn't, that will be expensive.

My car has 116000 miles.
My car has an automatic transmission.

Internal engine components each have their own signature noise. An experienced technician can often get a good idea of what is causing a knock by listening to the sound. A connecting rod bearing usually sounds off when you rev the engine up to about 3000 RPM then back off of the throttle. A main bearing has a low pitched knock that is stronger when under a heavy load. Bad pistons will also respond to load, but have a higher pitched sound. There could be any number of other causes of your engine noise and the best thing to do is have an experienced ear on the case. Contact Your Mechanic to have a technician come to your home or office to listen to your engine knock and advise you on what to do about it.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Loud knocking sound when engine is running

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: My 2008 Honda accord keeps misfiring on cylinder 2 and i don’t know what to do.

If the plugs are new that is unlikely to be the cause of misfiring. Compression in the No. 2 cylinder should be tested because if you have low compression or a sticking valve in that cylinder, that could cause a...

Q: Downshifts suddenly automatic locks

When you encounter the problem try and see if your cruise control works. If the brakes lights stay on, it will cause the cruise to be inoperative and affect the overdrive of the transmission and door locks autolock function. Come...

Q: Rocker arm would i know about it or car be normall

A broken rocker arm would definitely make a lot of noise and cause a constant misfire in the cylinder it is related to. My best advice would be to hire an experienced technician to look over the work to see...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.