Knock Sensor

[Kosmofreeze]

I've got a 5.7GXi-A. The knock sensor screws into a brass fitting (a tee) that extends from the block drain on the starboard side. The sensor screws into the tee such that it is parallel with the block. The 90-degree part of the tee is just a threaded plug that allows the block to be drained. The problem is sand and grit get caught in the 90-degree bend and plug up the drain. The only way to clear the sludge buildup when winterizing is remove the knock sensor and the fitting and blow it out ... then reinstall the fitting and knock sensor. If it was a straight-shot into the block I'm sure the "coat hanger trick" would clear the sludge but with the 90-degree bend I'm unable to clear the clog with out removing the sensor and fitting.

So I put it all back together and now I wonder if my knock sensor is still working. How do I know?

 

[cyclops222]

I would have to have a flashing Timing Light. To see if the change is correct.

 

[ESGWheel]

I am struggling to understand the concern. Did your device have a ‘port’ (a hole in the middle where it screws in) like a pressure sensor that you are concerned is now plugged up? A knock sensor does not have a port, it just screws in. So, all should be good, there is no harm in removing and putting it back in. There are ways to test a knock sensor, like this video (link). Otherwise, you would need a scan tool to see if the engine is throwing codes due a faulty knock sensor.

Why do you think it could be bad simply from removing and replacing it?

 

[ESGWheel]

Also, I found this picture of what is reported to be same engine as yours. Based on your description of not being able to clear it out because the drain plug is on the 90 portion of the Tee this picture appears to show the opposite > a straight wire would easily go thru into the block.

Others will know better the proper orientation of this and frankly I am usure it matters for the knock sensor, but it may be your drain plug and sensor are in the wrong holes of the Tee.

 

[alldodge]

Swap it around as ESG mentioned

 

[Kosmofreeze]

Also, I found this picture of what is reported to be same engine as yours. Based on your description of not being able to clear it out because the drain plug is on the 90 portion of the Tee this picture appears to show the opposite > a straight wire would easily go thru into the block.

Others will know better the proper orientation of this and frankly I am usure it matters for the knock sensor, but it may be your drain plug and sensor are in the wrong holes of the Tee.

View attachment 399659

One picture is worth a 1000 words - Yep, that's the fitting - very helpful. However, on my installation the knock sensor and plug were reversed. There is an engine mount or wire bundle that prevents the orientation as shown ... so, they stuck the sensor on the end and the plug at the 90-degree tee. My concern was that the sensor would only work if perpendicular with the block - some accelerometers only sense acceleration (i.e. knock in this case) on a single axis.

My solution - I found another machined brass tee with three 1/8" FPT openings and used a close-in nipple to attach it to the block. This gave me enough clearance so that I could install the sensor and plug as your picture depicts. If the drain plugs up now, the coat hanger has someplace to go!

I do have a Fox Marine gateway and have monitored the diagnostics for any knock related fault codes. There are none and the boat runs fine. There is also a diagnostic 'Knock' parameter that I presume indicates when the engine is knocking. It always says 'NO' - that's what made me suspicious that I may have disabled the sensor by changing the orientation. I'm also always suspicious (for good reason) that whenever I touch something ... it breaks!

I'm curious now - when your 5x GXi does have a bad knock sensor what are the operational clues that something is wrong?

 

[alldodge]

Is the wire long enough to move it to the other side of the block?

The sensor will pick up a knock "if working" from either side. Some motors have a sensor on both sides

I the early years of MPI the ECM would test the knock sensor each time the motor was started upon first throttle up, then not do it again until it was restarted. The issue came up as a code 44 if it could not detect the sensor

Problem came in if the user was using gas with an octane higher then 87, The next revision of ECM the test was done away with