I have a 1995 maxima, recently the engine started making this knocking noise whenever the engine is underload,

Question

The knocking noise comes from the engine I took it to a mechanic to get his opinion, he said isnt the timing chain, the noise only comes when the engine is underload(knocking noise) the noise goes away when the car is on idle, what could it be, please help

I have always used premium fuel eversince I have the car, the car has 153,000 miles. The noise sounds like an old diesel engine(knocking noise) I was searching the net and found some info. Some say it could be a exhaust leak(manifold), which I dont think it is cause I have fairly new headers. Others say it could be a loose spark plug. I was thinking about and engine flush to see if that gets rid of the noise.

Answer 1

You could have broken piston rings in one or more cylinders. Have him do a compression check.

We had a similar problem. When the car would go up a hill it would make a loud knocking noise, kind of like an old diesel truck. It turned out to be broken rings.

If it is a quieter knocking it is probably related to the anti-knock device or something to do with the ignition system.

Answer 2

Does your car loose power or become jerky when its knocking? If it does that would be a timing problem with the cylinders firing to early or to late. If it just makes a lot of noise under stress this may be more serious. It could be a piston or rod rattling under pressure. If your not ready to put allot of money into a 1995 you might want to think about a new car.

Answer 3

Knocking usually has something to do with the timing being too far advanced or the grade of fuel you are using.

Although your timing belt could be physically okay, did the mechanic check to see if it slipped?

And as far as the grade of fuel, you wouldn't happen to be using E85 would you?
MARK

Answer 4

Sounds like detonation.You probably need to have a basic tuneup and have the timing checked.You never mentioned the mileage.Sometimes a vehicle w/ a lot of miles is more prone to this.Your Maxima is built to run on regular fuel so don't waste your money.A tuneup/timing adjustment is your best choice and will save you gas.Good Luck

Answer 5

Poor gas, bad timing or knock sensor is bad...the noise you are hearing is "pre-ignition knock" Try putting in a tankful of midgrade or premium fuel and see if it goes away, if not, it's the other two suggestions.

Answer 6

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Answer 7

could be.
timing, poor lubrication, bad valve, bent rod, piston ring broken ( although you would end up with a more serious problem fast), timing chain may have skiped a tooth