Re: Engine knocking on low rpm... - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Engine knocking on low rpm...
Posted by Dean (more from Dean) on Fri, 11 May 2001 09:25:24
In Reply to: Engine knocking on low rpm..., philliprs-boston, Thu, 10 May 2001 23:13:27
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You have a high compression engine. The engine has developed a tendancy to knock. Possible causes are poor fuel, wrong or fouled plugs, faulty knock sensor, lean mixtures or engine deposits which create hot spots.
Inspect the plugs to see if they have suffered from the knocking, or display unusual deposits and coloration etc.
Techron Concentrate will remove the worst of the deposits, and will boost octane for the tank that it is in. If this helps and the knocking returns after the next fill up, then this would suggest an octane issue. If some of the injectors are not spraying properly and creating lean cylinders, then the Techron would likely fix that too. If your idle is not perfectly smooth and starting is not what it should be, then that would also indicate fouled injectors.
Inspect the knock sensor for soundness of electrical connections and physical mounting.
Inspect air ducts and hoses. Is there a leak allowing air to enter the intake system down stream of the air mass meter. This would generate lean mixtures. (But this should be detected as a fault via the O2 sensor.)
If you have under 100000 miles, then the fuel filter is probably fine, and not a source of fuel starvation. That would first show up as a loss of ability to accelerate with full throttle at high speeds.
The problem could be caused by a defective air mass meter as well, but usually these fail in more dramatic fashions.
Have you had any service work done of any kind? Is the battery in good shape (level)?
Engine air filter in reasonable shape?
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