8.1 knock sensor
 

Does anyone have any idea what would cause my knock sensor alarm to set off on my 02 8.1 ? It's always sensor 1 code and if I unhook # 1 then #2 goes off. I even unhooked the wires , it still went off, left the wires on and removed the sensors from the block, still went off ?????

fixx
 

clean the rust off the threads and screw them back in..clear codes ..if their still going off you may have a rod knock..

You cant unplug them, it wont close the loop.

It is a new short block and it still sent the code even though the wiring was still all connected but the sensors were just not bolted to the block. Mostly does it when getting on plane, sometimes after plane I can go full throttle with no alarm but then sometimes it goes into alarm as soon as I throttle it. I also replaced the sensors. Do the sensors have to be bolted to the block to complete the loop as well ?

There's a critical torque spec. Probably not the problem, just don't forget.

fixx
 

single wire?? if so then yes,,i have not worked on many 8.1's,,the older 8.2 and 7.4's the sensor screwed into the water ports on the side of the block,,they get rusty from the water and need to be cleaned and reinstalled and they had one wire goint to them and the screw in part completed the circuit..

2 wire sensors which makes me think that it wouldn't have to be bolted to the block to complete the loop. Motor sounds and runs great, all gauges read rite where they should. Pretty confident that its not actually knocking.

Too much mechanical noise in the engine will set it off. Or it could be knocking. It is almost impossible to hear it on a boat if you have through transom exhaust.

Does the alarm go off with the sensors off the block?

Loose valve adjustment, too much piston clearance, or any number of more fatal things.

What kind of fuel are you running? If you can run some better fuel in it just to test it will tell you if it is actually knocking.


Get a small outboard fuel tank & fill it with avgas or racing fuel. Run the boat on your main tank and see if you can get the alarm to go off, the hook up to your special juice & see if it goes away, then switch back and see if it does it again. That's what we used to do on the dyno before we started taking things apart.

Yeah they still go off even when they are not bolted to the block, that makes me think it could be in the PCM unit. Nothing but 93 octane always. Thanks for the info fellas, this thing is kicking my ass trying to figure it out :angry-smiley-038: