by maxim82, March 5, 2009
im new to this forum and to my car just got it a coaple of months ago but im feeling engine knock and bad gas mileage. on a prior car i had the knock sensor was the problem. but problem is ive got no idea how to ckeck it on this car or even where its located. been searching the forums but havent found anything that really helps. anyone out there that can help i would really appreciate it. thanks
Knock sensor on the (1999? Corolla - from other post) - is almost dead center of the engine - underneath the intake manifold. As for engine knock - I doubt it is the sensor, unless someone has tried to modify the engine - the 1ZZ-FE knock sensor is not known to be a trouble part. The engine itself is relatively noisy compared to the older A-series Toyota engines. Poor fuel economy has many causes - better scan the ECM and see if there are any stored trouble codes. I'm assuming that you looked into the simple fixes first (change oil, replace air filter, check tire air pressures, check plugs and wires, throw in a bottle of fuel cleaner, try running a tank of higher octane, clean throttle body, etc.)
If the engine has quite a few miles on it and hasn't seen the best maintenance (but you've covered all the usualy maintenance items) - very possible that the engine has heavy carbon deposits inside the combustion chambers and/or compounded by a bad O2 sensor. This engine has a unique piston/head design and if deposits are very heavy - will "ping" and detonate under load. Only true way to get that fixed is to clean the piston tops and head - not really worth it unless you need to get in there for something else (ie. fix leaking or stuck piston rings). There are quite a few fuel additives that might be able to help, but don't expect too much. Other option is to run higher octane and see if the pinging/detonation goes away. If it does - you have a carbon buildup issue, if it doesn't - you probably have an O2 sensor or something else to deal with.
