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Pastimes : Auto Repair & Maintenance Tip -- Ignore unavailable to you. Want to Upgrade?

To: Jon Khymn who wrote (63)	11/5/1999 7:29:00 AM
From: rustyjack	Read Replies (2) \| Respond to of 134

Knocking.... High mileage cars can begin to knock due to a carbon build-up in the cylinders, which increases the compression ratio, and thus the need for a higher octane fuel. But this is not as common as it was years ago. Knocking can also be caused by over advanced ignition timing ,but this too is not as likely due to electronic controls which automatically adjust timing. A knock sensor detects the knocking and sends signals to the computer to retard the timing. (It is possible the sensor has failed but not too common). Knocking is also a symptom of the engine running too hot. But the most likely cause IMO would be a problem in the EGR system (Exhaust gas recirculation). This system is used to dilute the fuel/air mixture with a small amount of exhaust gas, to lower the combustion temperatures in the cylinder. This helps prevent the formation of oxides of nitrogen and lowers harmful emissions. A carbon build-up can restrict the passages and reduce the flow of exhaust gas into the intake system. Or the system could be malfunctioning due to broken vacuum hoses or a faulty EGR valve or switching solenoid. It would help to know what kind or car you are driving as many models have problems specific to them only and would make it easier to surmise the cause.

To: Jon Khymn who wrote (63)	11/5/1999 11:08:00 PM
From: Greg from Edmonton	Read Replies (1) \| Respond to of 134

I agree with Ron's analysis of your engine's pinging symptoms. The first thing to suspect is the accumulation of gunk from the crankcase ventilation system into the combustion chambers. I would suggest to run some quality fuel-injector cleaner through the system, either Techron or BG44K or Redline Fuel System Cleaner. Those are among the most effective, yet are reasonably gentle on your engine. For a more extreme approach in cleaning combustion chambers though, you could try the GM product "Kleens". I am not sure if it is still available, as it is nasty messy chemical stuff. As I recall it is applied directly into the intake manifold with the engine running and causes the engine to sputter and belch smoke clouds out the exhaust, but is claimed to work very well for its intended application. I knew mechanics ten years ago that used to swear by that stuff how well it cleaned out an engine's combustion chambers. PS hey people don't forget to stop in at "Car Nut Corner", as the traffic's been pretty light lately: Subject 20243