Engine Knocking

[moune]

I have noticed that my engine makes a weird knocking noise when I am driving it. I don't know exactly what it is and was told that higher octane fuel will help remedy that. But since it is a LS, the highest octane is required already. So what is the next step up to take care of this problem. Please help.

[VMF]

do you have a check engine light on? when the knocking occurs? when you press the gas pedal or you hear it on a permanent basis?

[moune]

do you have a check engine light on? when the knocking occurs? when you press the gas pedal or you hear it on a permanent basis?

Well I disabled my check engine light when I install a new instrument cluster, because it stayed on all the time. It starts to knock when I give it gas.

[larryp]

Suggest you enable light and diagnose problem based upon code given. :whistles: If you're running the high octane already, you have another issue that may be identified by the trouble code.

[lexusjohn]

could be a faulty knock sensor :whistles:

[VMF]

you dont have to enable the light to get the codes, connect the scanner to your OBD port located under the dash and get the codes. you can also reset the codes from the scanner. knocking under the acceleration means either low percentage of the gas in the mixture, bad gas, bad knock sensor and many other things. you have to get an error code to find out what exactly is causing this, it might be misfire in one or few cylinders as well.

[JPI]

could be a faulty knock sensor :whistles:

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I never see the knock sensor on this vehicle goes out. Unless you replace the starter and damaged it.

JPI

[Shadow]

What year & mileage?

[bossman]

Where are you buying your gas? Although you are putting premium in, is it from a reputable dealer? You may want to only get gas from a well-known chain. Also, best not to fill up your car when there is a tanker truck filling up the station's pumps as this will stir up all kinds of sludge in the storage tanks.

[moune]

To answer the questions: 90' with ruffly 220,000, and I use Exxon, Chevron, or Shell premium gas.

[Shadow]

Yep, early 90 is what I thought. Your problem lies in the ECU exasterbated by high mileage so checkout the TSB for your year.

[VBdenny]

Are you saying that the computer causes problems on a 90 when it reaches high milage? I'll guess the TSB is the Technical Service Bulletin? Where do you find that?

[Shadow]

Are you saying that the computer causes problems on a 90 when it reaches high milage?  I'll guess the TSB is the Technical Service Bulletin?  Where do you find that?

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Both ECU & engine are the factors, and ECU replacement is the fix assuming the engine isn't out of wack. I found the TSBs on my AllData CD, and, the last time I checked, they were also readily available online and at the dealers.

Check engine error codes first before doing any repair.

[Shelly'sLS400]

Are you saying that the computer causes problems on a 90 when it reaches high milage?  I'll guess the TSB is the Technical Service Bulletin?  Where do you find that?

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Both ECU & engine are the factors, and ECU replacement is the fix assuming the engine isn't out of wack. I found the TSBs on my AllData CD, and, the last time I checked, they were also readily available online and at the dealers.

Check engine error codes first before doing any repair.

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I'm having the same type of problem. From idle, in gear, I get a little spark knock also. I'm running premium fuel and have no check engine light showing. Are you saying that the ECU is faulty because of high miles? I have 143k on my 90!!! Other than the little knock, engine runs great and plenty of power, fuel mileage is the same.

[SRK]

According to our owner's manuals, a little spark knock under transient conditions is completely normal, as the ECU runs the timing up to find what grade of gas is being used. If the knock continues under load, that's a problem, but if only during a rapid throttle opening, it is normal. Many engines experience this, and it causes no damage whatsoever.

If a tiny bit of spark knock was enough to damage a Lexus engine, I wouldn't have bought the car!

[jzz30]

do you guys have oil in there?

[pgupta]

According to our owner's manuals, a little spark knock under transient conditions is completely normal, as the ECU runs the timing up to find what grade of gas is being used.  If the knock continues under load, that's a problem, but if only during a rapid throttle opening, it is normal.  Many engines experience this, and it causes no damage whatsoever.

If a tiny bit of spark knock was enough to damage a Lexus engine, I wouldn't have bought the car!

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Quite likely, you need new spark plugs and cables. If so, you will find that over time, the problem will get worse at around 45 mph, 1800 - 2000 rpm.

[ECUPirate]

Ditto that on the plugs and cables. My old Chrysler started acting up as 'pgupta' described. I thought my transmission was out of whack. Turns out it was misfiring due to worn cables.