Knock Sensor replace on CTSC

[titaniumdave]

Does anyone have some advise for replacing the knock sensor on my CTSC 3.0 motor? I just put it back together and I am getting a front knock sensor code and it looks like I need to replace it. I was getting a rear sensor code before I rebuilt the motor but my local tech thought it was just the motor knocking, seeing how I lost the ring lands on 4 pistons and things were probably rattling around pretty good inside the motor. I did not mark front and rear on the sensors when I put the engine back together so I wonder if I swapped the position of the sensors and the code followed the bad one to the new location...

Bottom line is I need to get to the little bastard and I am looking for some advise about getting to it with as little dis-reassembly as possible. Can I pull the alternator and CT pulley mount off and get under the intake with out pulling the intake off? Has anyone else had to do this? Is there a test for the sensor other than testing the wires' continuity as described in the manual?

I just spent 40 hours of my life pulling/putting the motor back together and I would love to minimize how much time I need to spend finishing the job.

Thanks.

 

[Larry Bastanza]

Hi Dave,

If you look at page 11- 9 of the service manual you will see in the lower center of the page, just to the left of the ECU picture, it shows the two knock sensor inputs on D3 (rear) and D4 (front) of the ECU, you can try cutting and swapping the two wires to see if the symptom moves to the rear knock sensor.

Is it possible that during the rebuild the two sensors have been swapped in position?? Sorry, but I cannot answer your question about removal, have not been there.

The reason for the service manual checking the wiring only is due to the type of sensor it is (piezo, I believe) so you cannot check any static resistance like other sensors. I think the ECU actually tests them by listening to their outputs, so if the wiring is OK, the ECU becomes the "tester" for the sensors.

HTH,
LarryB

 

[Eddy]

Check my page out..
http://webpages.charter.net/eddyanm/traces2.html

If you have the right tool, you can check the signal on the KS.

 

[titaniumdave]

Thanks for the input. Larry, I thought about pulling the pins from the plug and swapping the position in the plug, from front(D4) to rear(D3). This won't tell me if the issue is a wire or the sensor, it would only make sure the ECU was working correctly. I have decided to pull the front knock sensor and check the wire for continuity, if the wire is good I will just replace the sensor. If the wire is bad I know what the problem is and I just need to figure out where I pinched the harness.

I think I can remove the CT pulley set up off the right side of the engine, un-bolt the throttle body from the supercharger and the intake from the heads. Once this is loose I hope I can 'jack' up the intake far enough to get to the sensor and wire with out having to pull everything off the top. I will post back after I am done.

 

[Larry Bastanza]

Eddy,

Great stuff. So feeding knock sensor data into some thing like the LM1 aux inputs will require a clamp to keep the input signal from going negative.

Thanks,
LarryB

 

[Eddy]

Well, the KS signal is actually very similiar to what you would get out of a microphone.. I think our ECUs (particularly earlier ones) uses simple filters to narrow down the knocking frequency.. But more modern computers may use better techniques.

And you are right about the sensor being piezo. If you hook it up to a scope and tap it with a screw driver, you can get signals in the range of 10 volts..

Eddy

 

[Cees-Jan]

" seeing how I lost the ring lands on 4 pistons and things were probably rattling around "

Did you already correct the fuel/air ratio, maybe your engine is still having a high speed knock !!!!!!

 

[titaniumdave]

A/F ratio was OK, 11.8 through out most of the range, never worse than 12. I wonder if the KS went bad and the timing did not retard quick enough. When the engine was re-built last time, 2 new pistons were used and 4 old ones, I think the 4 old ones are the ones which broke this time around. I will never know for sure.

 

[Cees-Jan]

Did you measure this rates on a powertest machine (sorry dont know the correct word in English), so under driving conditions at full throttle (flat out) or just with no gear engaged on your drive way???

This kind of damage is always caused by knocking, if you don't take out the problem which causes this than you will have the same result with your pistons soon


Remember, this kind of knocking cannot be heard, is also NOT DETECTED BY THE KNOCKSENSOR (This system was designed for the engine without CS)

 

[titaniumdave]

A/F was checked on the road with an LM-1 meter at WOT in real road conditions. I understand this is better than than on a dyno. I will check everything again once I am comfortable with how the engine is running.

 

[Cees-Jan]

OK, just wanted to prevent you from more trubles...

Are you sure you did not accidentially forget to plug it in, it is possible to see this (difficult) underneeth your throtlle body, way down.....

 

[titaniumdave]

I wish it was that simple. I can see with a mirror it is plugged in, plus I made sure to coat all plugs with di-electric grease when I put them together, double checked all connections over fear of them being loose.

I will be wrenching on Saturday.

 

[titaniumdave]

Back together!

The job to get at the knock sensor was not as bad as I thought it would be. I took off the belt and pulley for the supercharger, alternator, strut brace, EGR tube and throttle cable. Removed the bolts and nuts for the manifold connection to the heads and that was about all I needed to disassemble.

I was able to lift the intake manifold up high enough by tipping it toward the drivers side of the car, supporting it with a bar running from the strut brace mount to the top alternator mount, with the snout of the super charger resting on it. This gave me plenty of room to get in and unplug the KS, but not enough room to get a wrench or socket with a breaker bar on it in. I ended up using a mid depth socket and turning it with a pair of visegrips grabbing it's OD, to get the KS to start turning. It did take almost 2 hours to figure that out, but next time...oh I hope there is not a next time for this one!

Now the car runs great, drove 50 miles to make sure I did not get a code. Looks like happy motoring for me!

I am not really sure what was wrong with the old sensor, I popped the top off it removing it. The plastic was very brittle and discolored so I am sure it was a good idea to replace it. This sort of begs the question of why I didn't replace both of them when I was in there...maybe there will be a next time!