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View Full Version : KNOCK SENSOR

rockhead1
October 23rd, 2006, 10:44
Do all renix 4.0's have a knock sensor? I have a 90 4.0 out of an xj that I am putting in a yj and I was expectiing to have to move the knock sensor to put my motor mount on and there was not one.
BIGSLVRXJ
October 23rd, 2006, 10:47
Do all renix 4.0's have a knock sensor? I have a 90 4.0 out of an xj that I am putting in a yj and I was expectiing to have to move the knock sensor to put my motor mount on and there was not one.
They should, but they do run "ok" without one. It's quite possible whoever you got it from just removed it or broke it off in the removal of the engine.
rebel68
November 9th, 2006, 18:03
What do you mean by "ok" Do they run better with or wtihout or can you even notice a difference?
BIGSLVRXJ
November 9th, 2006, 18:07
What do you mean by "ok" Do they run better with or wtihout or can you even notice a difference?
I mean "okay", but not good. I wouldn't run without one for long. I did for about 45 miles it really screwed my gas mileage and power up. It's whole purpose is to adjust the timing to compensate for something (although I forget what now).
8Mud
November 9th, 2006, 18:08
Retards the timing some, when the motor pings (up hill, throttle mostly open, before it downshifts). It is likely more complex than just buying one and screwing it in. They say the torque spec.is kind of critical.
Without it, premium gas becomes a little more important.
BIGSLVRXJ
November 10th, 2006, 04:57
It is likely more complex than just buying one and screwing it in. They say the torque spec.is kind of critical.
Would you mind elaborating on this? I had never heard that.
old_man
November 10th, 2006, 05:14
First off, not all 4.0L's have a knock or ping sensor. Only the Renix computer equiped engines have it. It is nothing more than a glorified microphone. If it is supposed to have one and you don't have it plugged in, you can end up with some erratic engine operation. Noise can be coupled into the sensor lines and the computer will think it is hearing ping and will retard the spark timing. You will notice that the wires going down to the sensor are shielded. Ever wonder why. The input is fairly sensitive, and even with the sensor plugged in, false triggering due to electrical noise is a problem.

There is no way to add a ping sensor to the HO computer, it has no input for it. The ping sensor is why many people prefer the Renix controls for a stroker. The higher compression has a tendency to cause ping without premium gas. The sensor compensates.