Just did the dreaded valley hose on the 2004 Xjr. Thanks to the wealth of help and info here everything went rather smoothly 🙂 However, on the first fire up I got the "restricted performance" msg. Not cool after many hours and contortions. Didn't seem major, and other than the msg, the car sounded wonderful. I wasn't having problems with any codes before the tear down for the hose. Scan showed knock sensor errors. After a ride or two the check engine light popped on too. I began pricing replacements, and it seems they have become rather pricey. Just for giggles I decided to go back to basics and check the connector where the male knock sensor pigtail plugs into the female wiring harness. I had to disturb both of the connections when removing the water manifold. I tried spraying them with contact cleaner, but the msg and check engine light kept coming back, if not immediately, then after one start. SO....After using a push pin to remove the small, rectangular plastic piece with the two tiny holes, where the male pins go through, on the female connector, engine wiring harness end, I used the pin to gently bend the tiny contact that touches the male pin down some, so it would press on it firmly. It looked as if, over time, not only had the connections got dirty, vibration and stress had pushed that little contact upwards, making for a lot of room between the male/female connection. As soon as I did that, the restricted performance message went away, then I cleared the codes and the check engine light went off, and that was it. Drove it for 3-4 hours and 3-5 restarts. All is well for now and most importantly, for FREE. So if you do engine work anywhere around the knock sensors, or more importantly the connection between the sensor and the engine wiring harness, and suddenly you get random knock sensor codes or related restricted performance messages check this small detail, it might save some headaches and wasted cash.

 

First, sounds like good news.

While you were in there you should've changed out both knock sensors, especially if that hose under the supercharger was leaking.

Those knock sensors are very finicky when coolant touches them.

When you have a chance perform a resistance test on each knock sensor.

Any reading over/under 5% from an ideal 200 ohm reading is no bueno and the knock sensor is on "borrowed time".

Hoping for the best..

 

Failed to replace mine, when there replacing the intake gaskets, and valley hose.
I replaced the hose while there, it was still in decent shape, & not leaking.
If not leaked on, do they go bad???
Would like to know if i made a mistake.
By me not changing them, when i was there.

 

I would check resistance at each sensor. Hopefully, you nailed the fix. Now I'm tempted to go back and recheck my connectors (running a 1/4W 200 ohm resistor on each harness end) to simulate the knock sensor value until I can get in there to change them (and the valley hose, which is not leaking) out.

But, if I recall one of the KS sensors resistance was out of spec.

 

Drove to work and back today. All clear. No messages. So far so good. For Wingrider, if the sensors do go bad later on, get new, plug em in, and put them somewhere stable. The ecm will see the correct readings from the new sensor and things should be ok. Be aware though that the sensor can't hear spark knock happen, if you go the easy way and don't actually bolt them down in the factory location, so the ecm will not be able to retard spark timing, should it happen, and engine damage could occur. I did it that way on a previously owned Xjr, cause I didn't want to pull the supercharger, and never had any issues. Again though, l am a car guy and use only premium gas, and also know the sound of spark knock/detonation.

 

Wow. I wasn't aware that a simple resistor could fool the brain on these newer cars. I did that mod on all my old 4th gen lt1 camaros. Guess if you're not going to install new sensors properly, that would be the cheapest easy fix.

 

It's a very short term fix until I can get them swapped out, along with the valley hose. So far, so good...

I have new Denso units (in Advance Auto brand packaging... go figure, I'm lucky) ready for install..

I installed the resistor on the harness side and taped it up and tucked it away.

 

Am I right in saying that most of the sensors are just coils and the ECM can be fooled with a resistor?

I know that wheel speed sensors are coils but have to be replaced when failed.

 

Merion1;

I'm not a sensor expert but can share a little info on the subject. 'Sensor' is a functional description for what some may call transducers; a device that converts energy from one form to another. Your are correct; coils are common transducers either converting electrical current to magnetic fields, or magnetic fields to current. A common coil based transducer is a hall effect sensor; in the case of a flywheel or wheel hub, a magnet on the perimeter of the disc rotates by a fixed coil. Every time the magnet passes the coil a small electrical current is generated if the coil completes a circuit. The control modules (computers) for our cars can interpret these current pulses and them make decisions based on this info.

There are sensors for converting thermal energy into voltage (thermocouples), vibration/pressure/acceleration/temperature/strain to voltage (piezo), light to voltage (photovoltaic), current to light (LEDs), and so on. Sensor development and manufacture is a significant supporting technology in the automotive industry these days. Increased computing power (digital processing) in automobiles drives demand for sensors which perform the digital to analog, and the analog to digital signal processing. This is why we see so many sensors on automobiles.

The example of 'tricking' a control module by substituting a resistor for a inoperative sensor illustrates that the control module sometimes isn't smart enough to actually detect the sensor. Rather the control module senses another characteristic of the sensor (like the resistance of a coil or the resistance of another transducer).

Best Regards, William

 

Just an update- all is well so far with the knock sensor issue. Not one restricted performance message yet. Since I was on a roll I have gone ahead and done outer tie rod ends, new front tires, alignment (said wtf and got the 1 year package so if I do more work, I can get it redone for free) new front brake pads, and today I shoehorned in a gently used replacement driveshaft, and fuel filter while I had the plastic shields off. Man what a car. Makes me laugh to think I bought it for $2200 with 131k and drove it 3 hours home. You'd have a hard time building an engine that would get you from 0-60 in 5 seconds flat for that kind of cash. I got an entire car ��

 

I have a bad left knock sensor and bypassed it with a resistor, although I used I think it was 330k ohm to get the voltage up to about 3V. It is a 5 v supply, and I was getting low voltage fault. The voltage with the sensor plugged in was only about 1.5V.

Anyway I'm wondering if I need any new gaskets or will the old ones work for the upper inlet manifold etc. I can't find any of these gaskets on online Jag parts, or even RockAuto. And there is a hose under there I should replace too?

Bob

 

Yes, change everything while you have the SC off, including the valley hose and both knock sensors.

To trick the sensor - get a 1/4 volt 200 ohm resistor. I'll be more than happy to mail you two as I have 18 left...

 

Thanks but I already used a 330k ohm resistor and it worked.

Anyone ever used Standard Motor Products sensors from Rockauto? They have 3 year warranty. $83, $36.

 

Sorry to bring this old thread back to the surface, but I have the same knock-sensor issue currently and reading through the "quick-and-dirty" fi with the resistor I'm not sure if you mean

200 Ohm or
200 kOhm ???

I can believe that 200 to 330 doesn't make a difference, but this factor 1000 seems significant to me.

abonano mentions 200 Ohm, rcannon has fixed it with 330 kOhm, what's the real magnitude I need?

And thanks for the simple solution already, will definitely keep me ging until I have time to rip out the intake system.

 

OEM spec for knock sensors is 200ohms... +/- 5% but in reality when the sensors are good they are usually spot on at 200 ohms at 70 degrees F.

I was able to spook the ECM by installing 200ohm resistors in the harness, where the knock sensors connect.

All is legitimately fixed with new sensors though...