At the end of the 'Panic - Car Won't Start' thread, I mentioned that sorting the 'bore wash' problem had caused a 'Knock Sensor' fault, probably due to the popping and rough running after initial start-up.

So I did some reading up on the Forum, and came across DavidN's thread about the knock sensors, and how if they/one are not working the car will go into 'Reduced Performance' mode?

My car has the knock sensor showing up on the DTC check, and on the ODBII transmitter to my mobile phone. But...the engine runs like a dream, never been better?

I know I need to change it, but it's a tad confusing that my engine is running fine, and there's nothing displayed on the dash that i'm in Reduced Performance mode? Any comments?

 

Do you have an ohm meter to get resistance readings from both knock sensors? If so, post the readings back on here and I'll let you know if they are any good or not. Even though Jaguar doesn't have any ohm specifications on those early knock sensors, I ohmed out a brand new OEM Jag knock sensor for a 98.

 

I wonder if it will go away now the car runs OK.

 

Hi Addicted2boost. Yes I have an ohm meter, I will get these readings at the weekend and post them. What resistance should I be looking for between the connector pins?

Thanks

 

Hi JagV8, and thanks for your comment. I'm hoping it does go away, for some stupid reason I reckoned these devices to be around £20 or so, but on checking various sites for a new one...WOW!

But my car sounds better than it ever has done under my ownership, I'm sure it's down the the Engine Restore I put in with new oil and filter?

Maybe it's time to contact Eurojag again, or is using a 2nd hand part inadvisable in these circumstances in your opinion? I really am fairly useless when it comes to electronics, yes I understand the basics of measuring ohms resistance etc, basic circuits and wiring up general items. Modules, modern day vehicle wiring systems, ECUs, CANS, what's a CAN besides something to keep you coke in?

I may be baring my backside for a kicking here by showing and admitting my ignorance, but it all seems to be far too complicated? Maybe I can get a book on what I should know, anyone any ideas on such a publication or a website?

I will see about getting a sensor from the local Jag breakers, though I do read that they can be easily damaged.

 

Have you erased the knock sensor code to see if it would come back? They appear to be a rather sensitive device and can fail if over-tightened. I would hesitate to buy one from a breaker, but understand your concern.

The CAN is the computer area network used by the modules to communicate with the ECU.

The greatest source of information on the complex systems is this forum. I spent many hours just reading about problems and solutions before buying my jag, and still continue to do so.

 

Thanks RJ237. Yes, I did try erasing the error code, next start up it was back again. Car continues to run very well, seems much quieter than even before the bore wash episode? I decided to order a new sensor, should be here today.

 

What were your ohm readings on those knock sensors?

 

I'm sorry 'addicted' I haven't done them yet, been off poorly from work. Never had a flu episode like this in 60+ years!!

 

Google knock sensors: lots of useful threads; seem to remember there is an equivalent knock sensor (maybe for an X-type?) that was a fraction of the cost of the X308 sensor, with only issue being a slightly longer piglet. You might also try spraying the sensor with electronics cleaner and check to make sure the connections are good and there are no broken wires before buying new ones.

 

Jhartz, I know which knock sensors your talking about but, this is in regards to a 98' XJ8 (AJ26). These sensors are a bolt style vs the 99' on up is a stud style. They're $86 on Rockauto.com which isn't bad for a 98'.

 

I've now got the new sensor, I am fitting it at the weekend, will keep you all posted. Next job is the Transmission Oil Cooler pipes (been told it's a difficult job so not looking forward to that). Paul.

 

If these are the bolt on type, look up the torque value and do not exceed it. The sensors are a high precision device and the torque matters.

 

Hi All. Fitted the new Knock Sensor, torqued it down to spec, error has gone. There is no change to how the engine runs, seems I 'got away with it' while the bad sensor was attached? I am almost certain that the 'popping & banging' from startup after the bore wash is what caused the original sensor to fail, maybe worth pointing out to anyone with bore wash in future? Thanks to everyone for their very useful posts with this problem.

 

That's again good news!

 

I think the knock sensors are supposed to run right at 200K ohm on testing.

But I have a questions: On other cars (namely GM V-8s) with the engine running you can test the knock sensor(s) by tapping on it with a hammer. The knock sensor detects this as a knock and advances the timing and riches the fuel air mixture so the engine revs slightly, but very noticeably.

Has anybody heard of testing our knock sensors this way?

 

Can you just tell us what the normal ohm readings are before he posts his???

 

I'm bumping this to see if anyone has a comment about this crude way to test a knock sensor. I have checked the sensor and gotten the correct 200K ohm reading but I still seem to get a little "rumble" on the in question bank from time to time.