draylorn

I have recently purchased a 2000 Lexus RX 300 AWD w/97K miles. I have spent considerable money trying to get rid of a spark knock noise, even using premium gas. No error codes have appeared saying there is a problem and after all the sensors had been checked, the Mass Air Meter and Air Fuel Ratio Sensor were replaced and all the rest of the sensors checked good. This did help a little, but the pinging is still there on a daily basis. I was able to get the previous owners maintenance papers, and it appears the problem first appeared at the 75K mile service at a Lexus dealership, in which the Lexus mechanic noted it was injector noise and is normal, but my mechanic says that is not the cause, nor is it normal. Any help would be greatly appreciated.

Lexmex

Welcome to CL

When do you hear this noise, all the time, and is it more pronounced on some occasions and not others?

draylorn

As is normal with spark knock I've experienced, under load moreso than on flat ground, but even when not under load you will hear it, especailly while it is shifting through the gears.
It also goes from no pinging when the car is cold to progressively worse as the engine gets to normal operating temperature.

salimshah

Preignition is hard to remove if it is due to carbon buildup in the head. It also may be too premature to reach the conclusion above. I have not used additives like seafoam (sp?) or similar. You may like to read up in the maintenance sub-forum. Here in RX forum I have not seen too much discussion but another brand (the name escapes me) has been mentioned. TunedRx maybe??

Related to preignition, I once had low coolant in the engine block and that caused pinging under hard acceleration after reaching operating temperature. So with engine COLD open the radiator cap to ensure the coolant is all the way to the top and there is coolant at least to the min level in overflow reservoir.

Nearing 120k you may be tempted to change the plugs yet once again. A good mechanic can look at the plug and deposits and suggest the "hot" level shift. On second thought, it takes a bit to develop carbon on the plug, so it would have taken couple of months from plug change.

Salim

HarrierAWD

It may be the classic carbon deposit issue. Once confirmed, there are three ways to go about this:

#1 - Use GM's Top cleaner. Remove all plugs and pour the thing into each cylinder. Let it sit overnight. Cover the engine with a towel. Crank it the next morning until all gunk shoot out from the plug holes. Put the plugs back then run the engine again. It will smoke like a mo fo for a while, but this is the most thorough way.

#2 - Use Berryman's Chemtool #12. Add to gas. This may take about 3 tanks of gas, but it does the trick to my old GM car. Most convenient way for the backyard mechanic. Don't bother with Techron, Gumout or STP. They don't do jack.

#3 - Take the engine apart and clean the pistons, piston rings, and the back of the valves. Have a shop do this.

Once the engine is cleaned up, do not use premium gas in your area. The octane may be too high. Use mid-grade or regular gas to avoid carbon buildup again.

draylorn

Thanks to both of you above. I appreciate having some direction and will try your reccomendations.

TunedRX300

You may ask your mechanics to perform the surgical removal of carbon buildups but before you spend couple hundred of $, try with OTC fuel additives that have a strong dose of carbon removing additives such as PEA.

See this thread
http://www.bobistheoilguy.com/forums...296612&fpart=4

Chevron Techron Complete Fuel System Cleaner, Gumout Regane Complete Fuel System Cleaner, Redline SI-1and BG44k all have PEA, but at different level of concentration.

Please use the specific products I named above, for example only Gumout Regane (yellow bottle) should be used, not the cheaper fuel injector one.
Redline you can buy at Pep Boys, Gumout Regane at Autozone and Walmart, BG44K is avaliable only at dealers and the most expensive.

Just pour 1 bottle per full tank of gas for two treatments in a row and see whether carbon build-up is gone, $10-$20 solution is certainly worth a try.

lexus114

Maybe a defective knock sensor?

salimshah

We all overlooked the obvious ^^^^

Salim