pitm96

i have a bad knock sensor on my 1994 toyota pickup 3.0l v6- this is located in the block between the heads- evidently it senses engine detonation and sends a signal to the ecu- my question is - do i need it- will it destroy gas mileage... etc- why exactly do i need this

eric-the-red

Like you said the knock sensor senses detonation, and then tells the computer to retard the ignition to stop the detonation. If you're engine isn't knocking then the sensor isn't doing anything. If you're engine is knocking and the sensor isn't working then you could damage the engine. As for gas mileage I don't think it would have any effect.

The sensor is a PITA to get at for replacement, you have to remove the intake manifold. Apparantly the sensor wire goes bad sometimes, that could be the problem, but it's just as much work to replace.

Dave Mooney

Hey guys, I don't want to damage an otherwise great running 3.0 head gasket rebuild on a 94 4 Runner SR5.

What is the cause of detonation knock, valve knock, engine knock etc.

What does it mean if the sound goes away when the engine is warm.

What remedies, adjust timing some more?
Please advise

Weasy2k

Detonation and pre-ignition are forms of abnormal combustion in the combustion chamber. During normal operation of the engine, the burning of the fuel-air charge produces a steady, smooth push on the pistons of each cylinder. At the instant of ignition by the spark plug, the flame of combustion moves rapidly outward from the plug very much like the waves when a stone is dropped into a pool of water.

Abnormal operation (aka to lean or to much timing advance) may allow combustion pressures to develop so fast that the heat and pressure will "explode" the remaining unburned fuel. This produces the knock, often called "ping", carbon knock, etc. Actually this is detonation. The knock results from the violent explosion when the normal flame front runs into the secondary flame front. Detonation will cause piston and ring damage, top ring groove wear, scoring, sticking rings, loose head gaskets and possible complete engine failure.

Now what those knock sensors do is detect this happening and sends a signal to the ecu, then depending on how strong the signal is the ecu will retard the timing to help get rid of the detonation problem. Sometimes what kills the knock sensor is a loud banging or a sharp hit of ping/detonation. Some people have killed those sensors by hitting the block to get something out (stuck alternator or something) as they are very sensitive.

The sensors turn on above 3k rpm where they are really needed becuase below that the engine block can take the beating vs up high when its under sever load.

What happens?

detonation caused damage


Pre-Ignition damage


both really suck!

Dave Mooney

Weasy2K: Thanks please read head gasket removal thread some of the last posts. I rebuilta 3.0 vze and it seems to be running fine; however one morning I did hear what I thought was an unusual knock, after the engine warmed up it went away. Timing is set correctlly, could an out of adjust TPS casuse such a thing. Have logged about 1500 miles since the rebuild without any problems. One other post has this mystery knock but his seems to be everpresent at low rpms, doesn't sound like the danger area above 3Krpms.

Any ideas as to his "mystery knock" would be appreciated. Just hoping my rebuild holds up.