I have a knocking sound in top of engine

The owners manual probably says no. Most say 89 octane is the lowest. Look in manual if you have one or they are typically on-line. With that said, test your vehicle with that fuel. Next time it is very close to empty put 2-3 gallons in the tank and drive. If the octane is too low the engine will "spark knock" or "diesel" (a rattling sound from the engine upon acceleration caused by fuel pre-ignition/detonation). If that happens put an equal amount of premium fuel in the tank and the spark knock will go away. Short-term a spark knock won't damage an engine, but longer term can by causing over heating, vibrations, abnormal stresses ... hesitation on acceleration - poor mileage and poor engine performance. If you are able to use 88 octane-15%, without getting a spark knock, make sure you check your mileage and see if, or how much, it drops. Lower octane and higher ethanol both reduce mileage. What I always told my gas customers was to check your mileage with different octanes and see what octane gives the highest mileage (and then do the math and see if its cost effective). Say you use regular normally and you get 30 MPG. Then you try the mid-grade and get 33 MPG, so you try premium fuel but you still get 33 MPG. In that case the mid-grade is your best option, assuming that your 10% increase in mileage cost you less than a 10% increase in cost! But you do always stay away from fuel that causes a spark knock.
The rule of thumb is: The higher the octane the cooler the combustion, therefore the lower the octane the hotter the combustion. Higher ethanol means that the engine is running a little leaner and a little hotter.

If it sounds like a sort of knocking noise, it could be that you are using a gas with to low of a octane level. See what happens if u put higher grade gas in or go to auto parts store and try a 5 dollar bottle of octane booster on your next fill up. If that quiets your noise that could be your problem.

dear user,
In some cases, gasoline problems cause the irregular combustion that leads to knocking sounds in an engine. This can occur because of problems with gasoline octane. Gasoline's octane ratings signifies the amount of compression the fuel can handle before spontaneous ignition. When this spontaneous ignition happens instead of the normal ignition, knocking may occur and can cause damage to the engine. The lowest octane gases are typically the least capable of withstanding compression and are more likely to ignite this way.
Sometimes the sound of engine knocking is caused by something other than the typical combustion process problems. For example, some types of mechanical issues may cause these knocking sounds. Such mechanical issues can include defects in the crankshaft bearings, broken flywheels, and water pump bearings that are worn out.

faisal

Hi, is this a new noise ? If it is check the oil level as shown on the dip stick of the engine..... if you can hear knocking the engine will be pretty well buggered. How many km\'s has the vehicle done.... really, not what you can see on the speedo. One other thing is if the wrong fuel has been put in the tank, i.e diesel, or high octane petrol that the knock sensors cannot adjust to suit i.e av gas is a very high octane rating fuel that should not be used in engines designed for low octane.

According to page 10-3 of the 2001 Nissan Maxima Owner's Manual:

FUEL RECOMMENDATION
Unleaded premium gasoline with an octane
rating of at least 91 AKI (Anti-Knock Index)
number (Research octane number 96)
If unleaded premium gasoline is not available,
unleaded regular gasoline with an
octane rating of at least 87 AKI (Research
octane number 91) can be used.
However, for maximum vehicle performance,
the use of unleaded premium gasoline
is recommended.

Engine "knock" is not just an unusual sound - but over time can cause real damage to the engine. You *should* use fuels with the recommended octane levels, but if you choose to use fuel with a lower octane level due to reduce fuel costs - do not repeatedly use fuel that causes engine knock. Find the "sweet spot" between the cost of lower octane fuel and an octane level that does not cause knocking. Expect fuel economy and performance to drop with lower octane fuels, too.

Good luck!

If it's a 3800 you need to get a new balancer. They com apart and rattle. If the oil light is on and it is knocking that may be a bearing problem, but 3800 very seldom does have a bearing problem.

Depending on what Audi says about fuel required to run your engine. Regular fuel could cause you problems in regards to engine pinging and noises. If you have your owners manual, check and see what fuel or OCTANE quality Audi states should be run through your engine.

If your not sure what I mean by Octane, I'll explain it. Octane is a rating given to a fuel, the higher the rating the better ignition within the cylinders of your engine.

Next time your at your local gas station look at your pumps, and you'll see numbers under Regular probably around 89. But the more expensive fuel has a number like 94. This is why you pay more for the fuel. This number is stating that it burns cleaner and more efficent. This may be what your car requires, that the engineers at AUDI say is required to properly run your engine.

However, make sure that your oil level in your engine isn't over filled this could also cause vehicle back fire, popping noises. But so could a lot of things, hole in your exhaust, near catalyatic converter. Hope I've given you some help.

Try higher octane and decarbon engine. fuel filter good idea also. sounds like detonation

code 43 throttle position sensor out of adjustment.not working.if you replace knock sensor and it still spark knocking.make sure the wire connector is not broken.go to higher octane gas .make sure engine timing is correct. also make egr valve is opening when it suppose to it will cause detonation.you will need a scanner to check tps and egr valve.