Skip the auto shop - Our mechanics make house calls

Q: My system says there is water in the fuel

asked by on

Notice a little knocking when slowing down running rough and clears up if I punch it it don't knock will water cause knocking

My car has 300000 miles.
My car has an automatic transmission.

A: Hi. Yes, water in the fuel will cause knock...

Hi. Yes, water in the fuel will cause knocking. I would advise doing a fuel system maintenance - drain the fuel system all the way to the tank, including the tank. This will get rid of any water and contaminated fuel.

I recommend replacing the fuel filters. If after servicing the fuel system, the knock is still there, most likely you have a sticking fuel injector and the injector will need to be replaced. If you would like to have this checked in person, a certified technician from YourMechanic can come to your location to diagnose the water in fuel and follow through with any needed repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Car is running crappy sounds like a v8 truck with dual exaust.

If the engine exhaust sounds very loud, there may be a loose or broken component like a cracked manifold or rusted pipe section like on your egr valve. A technician will be able to look over the vehicle listening for...

Q: engine wont start

Hello, thank you for writing in. There are a few basic tests that you can do in order to help narrow down the issue. First turn the vehicle to the "On" position, and listen for the fuel pump to prime....

Q: Advice on buying a car with hail damage

Realize that hail damage is just pieces of ice falling down on the car and denting the heck out of everything. It may look horrible but the actual hail itself doesn't damage the car. So as long as it runs...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...