Random misfire got worse and never threw up codes. I saw a few other threads so this may help them. When I bought the vehicle about 5k ago the indie dealer did a lot including new plugs which I think was an effort to clear the misfire that I didn’t feel until later.

My reliable current shop has diagnosed faulty knock sensors and mentioned something about the loom to those under the car. I asked why they are replacing the plugs again and they say they are burnt from very high temps from faulty sensors which if left untreated could burn out the valves. I’ve been driving for about a year but only about 5k kms so I’m keeping my fingers crossed.

 

I would be very surprised if the OBD system did not report a knock sensor problem as these sensors are a major component and a fault will often result in a complete engine shut-down if the ECU cannot correct the issue. However, all things are possible.

Richard

 

Many start playing the "swap a part" game before performing a root cause analysis. Out of interest... do you have all the codes?

 

No codes ever came up and fault was barely noticeable for a while. My shop was right with an intermittent starting issue and I reluctantly agreed to a new starter and never any issues since. They have ex Jag service personnel there and they seem certain about 2 of the 4 knock sensors which I’m guessing come as a pair on one loom?
I wouldn’t call inspecting damaged parts and then replacing them swap-a-part but you might be right. will report back in time…

 

I wonder how reliable this current "reliable current shop" is?

 

I have a minor miss/stumble at idle that has never triggered any codes or warnings. I'm actually leaning towards the issue being injectors, I've had new plugs etc and the minor miss has stayed the same (mainly on one bank). Only really at a low idle, very smooth everywhere else. Will follow this with interest.

 

I'm confused by your post @alanroberts50 . Did you have the knock sensors replaced as well as the plugs? You mention they diagnosed the knock sensors but they replaced the spark plugs and the starter. If you had the knock sensors replaced, try and retrieve them from the shop. They are easily tested. In the meantime, please clarify all the work you had done. you also noted "they mentioned something about the loom to those under the car". Do you have paperwork showing the work they did? might be helpful. cheers.

 

if you read my post you would see very so far.

 

I had terrible shaking from a misfire about 2ys ago on my 2013 xk with 40k km on the car at the time. The fix was to replace the spark plugs and it's been great ever since. If that didn't work coils would be next. However, in my case codes came up so the mechanic wasn't blindly guessing.

 

The starter motor was months ago and nothing to do with the misfire, it was an example of how they have been right with their recommendations so far.
They haven’t done ANY parts replacement yet on the misfire! Just diagnosed it and provided a quote.. The only reason I even posted was that it might help others who have been tearing their hair out trying to diagnose a random misfire. please just wait until the work has been done and I will report.

To LJRXKR poster. I started about a year ago with the same thought in mind and wasted money on fuel system cleaners until it got worse.

 

deleted.

 

I understand

 

It finally threw out a code p0327 which led them to replace 2 of the four knock sensors. I (i’m assuming it’s 2 per bank). I can’t feel any misfire now but they say when they reopen after the holidays there is a “short link harness” buried in the v of that bank that needs replacing to complete the job as it is corroded. They can’t get it until after the holidays but it’s already feeling like no misfire.

 

Did you possibly keep the old sensors? Would be very interested to know the difference between them. Was your misfiring at idle or throughout the rev range?

 

Don’t have the old parts. My misfire started randomly at idle then graduated into slow speeds then kind of randomly throughout the range.

 

Can you show these 4 knock sensors?
I have never seen more than 2 but am willing to learn?
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I also thought that there was one in each bank but I have a 4.2 which does only have two.

Richard

 

same with the 5.0. This is why I all my friends and family to retrieve the replaced parts when they have work done. it's actually a law here to keep and make the parts available. but we'l get more info after the holidays I suspect.

 

Thanks guys for the info. Ok great if there’s only 2 then they’re all new now! Just have to wait for the short harness link they mentioned to arrive and get that fitted after the holidays.

 

Well with what they told you did they actually change them? They are hidden and you won't be able to tell new from old? That's another reason to ALWAYS ask for the old/replaced parts.

Pictures would help too as it does not make sense that the plugs got burned out because of a bad sensor? What sensor and where are the codes? These types of comments point to someone who has no experience with trouble shooting cars? Now maybe we are not getting exactly what they said because it's gone thru several people?
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