knock sensor--knock it off

[kleinkid]

'94 SS--knock sensor CEL, changed sensor, did wire checks per FSM[not 100% confident of that process], put in different ECU. Still have CEL, reset ECU and did clear codes with the green and black sensors connected.

Then ran new wires for both the signal and ground. Used weather proof butt connectors inside the engine compt., and used a 2-terminal shroud assemble(WeatherPak type) inside cabin. Cut the wires and used butt connectors to splice the terminal leads to the newly run wires and the two wires coming off of the ECU connector. Still have the CEL, am sure it is in limp mode because can't get boost up and performance is anemic.

Would it have been better to disengage the signal and ground pins from the ECU plug, remove the old wire remnants and then solder the new new wire ends in place, and re insert the pins back into the ECU plug? Not using the 2-terminal shroud.

Of course, maybe the knock sensor is working, and the engine has knock.

Does it detect a knock caused by bad bearings, and/or just combustion knock?

[ericem]

CEL shouldn't be on if he sensor is indeed making its signal to the ecu interference free. I am confused about your post though, is the original wire still attached?! If so remove it the grounded shielding is most likely shortening out.

[kleinkid]

Both ends of the old wire are not connected to anything, signal or ground.

[Florin1]

Hey John. When I couldn't get rid of my know code, i went to Guitar Center and bought like 5' of shielded mic wire. It was like $1 a foot. I cut half of the old wire off, and half of the knock sensor wire too (yes i eliminated the little connector, since it got crushed on my transmission swap) and spliced them both together. I just cut the wire longer than i wanted, and folded the shielding wire back, like 1" on each end. Butt connected it on either end, folded the shielding over the butt connector, and electrical taped that, and finally shrink tubed it. Finally no CEL. I was stoked. FWIW

[kleinkid]

Some say that you don't really need a shielded wire. That is why I ran a separate wire for the ground and one for the signal.

[ericem]

Why did you run a seperate wire for the ground? the knock sensor just grounds to the block.

[n2x4]

Knock sensor is a single wire sensor. The "ground" at the ECU is just the termination of the wire shielding.

I too ran mono microphone cable from radio shack to replace my knock wire from the factory harness. 2 years and no troubles.

[kleinkid]

What worked for some one else as far as what was done with the ground wire is good for them. Running a ground wire as I did, should have no negative effect. Others have run an unshielded signal wire and have had no problems.

Could the two terminal connector I used at the ECU end of the wire be not allowing the signal to get there cleanly?

Would it be better to pop the pins out of the ECU harness plug and solder the wire ends directly on to the pins? Instead of using the terminal connector or butt conectors.

[Legacy777]

Just a tid bit of info, the stock knock sensor wire from the ECU grounds the shielding at the ECU. The knock sensor itself also has a shielded wire and grounds itself through the block. You do not want to have the two grounds from each wire touching.

John, as for the spade connectors. I'd suggest soldering the wire to the ECU pin wiring. The ouput from the knock sensor is in the milivolt range, so any increase in resistance in that wire can cause issues with the knock sensor circuit.

[kleinkid]

Josh-- as per your first, ground wires are OK.

second, I was wondering, if the connector I was using would have an impact for the reason you suggest.

Yesterday, I moved the knock sensor to a bolt hole on the flange at the bellhousing. Kind of cheating, was told the Subaru dealers in Austrailia put it there to get to a less sensitive area because the early legacy knock sensors are overly sensitive. Didn't start it because ran out of time and wanted to watch the Rose Bowl.

Did pour Seafoam into the IAC, and it is soaking. Will go out now and start the car, get it warmed up, then connect up the connectors and see what codes come up. Will update later.

[Legacy777]

If you have a multimeter, check the resistance of the knock sensor wire from where the sensor plugs in to the ECU connector pin. You should have 0 or near 0 ohms.

[kleinkid]

Still have the code 22.

I bought a digital meter that reads low numbers.

OK, I don't understand where you want a resistance reading. Do you mean at the back of the cluster that plugs into the ECU? Check location B56.5?

[magicmike]

With a meter in continuity mode (buzzer when both terminals touch) the knock sensor should NOT be to ground if it is in working condition. Its basically like a shock sensor. Picture a metal ball suspended with a spring on the top and bottom in a metal tube but is not touching the sides. The metal ball is connected to the ECU and th metal tube is the engine block which is grounded. At rest the metal ball does not touch the side of the tube completing the circuit if the engine shakes "knocks" hard enough the springs expand and the ball makes contact with the side of the cylinder completing the circuit to ground and giving the ECU the code.

Hope this helps explain what the thing is and hoe it works.

As for the shield, I'll explain a bit on that. The purpose of the shield is to be connected to ground on the ECU end and NOT at the sensor end just like Josh says. This is because any interference that may be picked up by other cables such as electrical "eddie" currents will be "soaked" up by the shield and carried away from the sensor and back towards the ECU. Any shielded wire is aways grounded only on one end and it matters which end is grounded. Its always grounded such that the "noise" is directed away or in the reverse direction from the signal path.

hopes this sheds some light on these things.

[Legacy777]

Still have the code 22.

I bought a digital meter that reads low numbers.

OK, I don't understand where you want a resistance reading. Do you mean at the back of the cluster that plugs into the ECU? Check location B56.5?

Yes, connect one of the meter's probes to the ECU connector Pin B56.5 and the other probe to the chassis side knock sensor connector in the engine bay. At the ECU you can either back probe the connector, or you can disconnect it from the ECU and probe it from the front. Just make sure you get the right pin. Remember that when looking at the ECU I-O the image is as if you're looking directly at the ECU connector, so when looking at the ECU plug when not connected, you'll be looking at it as if you're looking into a mirror.

Also, I've found that using a small wire with alligator clips attached to the meter's probe works well for probing the ECU connector pins since they are pretty small.

Let us know if that still doesn't clear things up.

[kleinkid]

Finally, the CEL for knock sensor is gone.

Used shielded 24 guage stranded 2 connector audio cable, purchased from Radio Shack. Soldered to one pin on the conector that plugs into the knock sensor conector. Used one of the stranded wires as the signal wire, and used the shielded wire as the ground on the ECU end.



The light was gone when restarted the car. No longer in limp mode. Can hear the turbo now.

[Legacy777]

Awesome!

More than likely the stock wire is cracked. I ran into this on my car when doing my Link install....stock wire had to be bypassed.

[kleinkid]

Guess what? Discovered that my first attempt to fix this thing was a sure failure. I had soldered both the ground wire and signal wire to the pin of the harness side connector at the connector to the knock sensor. It had been a while since I did that and didn't discover it until looking at the remnant sitting on my work bench. So, everything I did after that, until fixing it correctly was going to fail also. Magicmike and legacy777 provided good training information. Now it makes sense to me. TRAIN, TO UNDERSTAND. Don't just train to perform the work steps to make the repair.

[Legacy777]

TRAIN, TO UNDERSTAND. Don't just train to perform the work steps to make the repair.

Very good words of advice! Once you understand, doing the work is pretty straight forward.