Just put 950 miles on the car over an overnight trip to Austin and back. Very enjoyable and trouble free drive. No issues of any kind to report.

Had the good fortune to trail a new C-8 Corvette over a deserted stretch of highway with both of us running about 125-130 mph for at least 20 miles. The old XKR really enjoyed the exercise as much as I did.

In fact, the car runs so well with one knock sensor relocated that I’m tempted to do the same for the other one

​​​​

PS. the ‘Vette driver and I both pulled over in Paris TX and had a nice time looking over each other’s ride before going our separate ways. He was more than a little surprised at how well behaved the XKR was at moderately high speeds, & definitely envious of the more comfortable seating. I believe the guy was more than just a little saddle sore from his rough riding Chevy.

Z

 

avos save your breath.

I tried to explain exact same thing and I got the exact same result. Actually I think at the time the OP didn’t believe that timing was being constantly adjusted which it is. If the system increases the timing until the onset of knock and then slightly reduces it he’s gonna be blowing up his car in short order as the tops of his pistons are slowly eating away one small dink at a time.

The service manual instruct you specifically to ensure that the knock sensors are bolted down to an exacting torque narrow because The pressure on the case affects it’s reading. That’s how sensitive it is and how it must be located elephant location or else the timing to slowly pin your motor apart. And just because he can’t hear it doesn’t mean it’s not happening. Using a magnet on an acoustic sensorHas the effect of dulling it. Soooooo the ECM will never see the correct signal. However maybe with a magnet it causes the timing to go fully safe and he’ll live forever with reduce performance? I don’t know. But what I do know is I have detonated the top of a piston off before and I’m not gonna do it again

 

Blowing up my engine in “short order” is taking some time . After my recent trip, I’ve got over 2,000 miles on my little knock sensor hack, all without the sky falling.

Actually, mainly to satisfy my curiosity, I am regularly examining piston and bore condition with a typical endoscope. Still in perfect and as new condition. Pistons in banks are identical. Ignition timing is unremarkable.

I’ll report back at 1,000 mile intervals, or sooner if the joy ride turns into a train wreck. Adios .

Z


.

 

If he would want to drive his car of the cliff, that's his choice, he is free to do that.

For me its important that everyone here has correct information on the topic.

The magnet will indeed as you say ensure there is no chance anymore that the ECU will be able to detect any knock, just placing it somewhere else jeopardized that ability already of course. As the ECU is hacked to think the knock sensors work, and its not getting knock signals, it will not do anything and thinks all is good.

Its like carefully packing the Crash sensors with foam in a safe place and keep it connected to your car, so no safety concern codes are being displayed. Unfortunately there could be an event where the airbags have to deploy to protect you, which has now been disabled.

Its a risk you take, for some it may workout in the end that nothing happens, but not for all...

The risks can become higher with older engines, as there mixture imbalances between cylinders can be higher enhancing chances of knocks for the leaner ones so its hard to tell how much risk you take. There are more things at play as well that can enhance the chances for knocks, so again one experience doesn't safeguard you from it all.

Higher octane fuel does help of course, but if that's enough is not something I can't guarantee.

 

Let’s keep in mind that the right bank knock sensor is still in the factory location and working just as the wise engineers intended


Z.

 

By short order I mean within the next year. When detonation occurs it blows couple of molecules of aluminum off the top of the piston. in order to get through the top of a piston you need several months of this to happen

I don’t know why you appear to be so flippant to us when all we are trying to do is help but you seem to be taking this as a personal attack or criticism. Please don’t. I’ve spent my life troubleshooting complex circuits and I’ve worked on cars since I was 14 and I’m 56 now. As an electrical engineer who has worked various defense and space programs, I have learned a small signal anomalies or circuit failures can accumulate over time and cause a disastrous results when it finally lets go or takes out a bigger system. I understand how these cars are designed and how they use various feedback sensors and mechanisms to fine tune adjust the operating parameters and when you fuel the system by giving it incorrect sensor data it will do the wrong thing guaranteed and just because you can’t hear detonation It doesn’t mean it isn’t happening on a very low scale. Even with that nation that you can hear it will still take a month or two to blow through the top of the piston. I remove some of my spark plugs and look for the dotted signs of aluminum transfer to the white insulation to see if you have a technician occurring as you’re not aware of

 

I’m pretty well versed in what detonation looks like, and piston failure can happen in under a hundred miles, as well as the slower process as you mention.

I started a career in the automotive and motorcycle service industry in 1969, that’s over 50 years ago if you have trouble with the math.

In 1969/1970, while working at Triumph of Oklahoma City motorcycle dealership, every summer we had a slew of customers coming in on I-40 from Amarillo Texas. They limped in to OKC on one cylinder. The bad cylinder usually had a swell hole in the piston from detonation.

PS: Since these travelers were miles from home we gave them priority and usually had them fixed up on the road again the same day.


Z

 

I have some spare knock sensors that I removed from my STR when I replaced my valley coolant hose. I’m gonna run some test on it today to see what happens to the output when I put it next to a very strong magnet. You might be completely safe as I said earlier it might be the magnet is causing the timing to retard fully so you never detonate. If that is the case then I will admit that you will not destroy your engine but you will not get full performance so it is a good hack to get you through until you can replace it

 

ok cool man. Im just trying to help and learn too

btw im in little rock

 

I really am impressed by the amount of interest this hack had garnered.

I would describe the magnet I’m using as refrigerator type strength, if that matters.

Just going by my current rate of piling on miles, and estimating when spring will bring warm enough weather (by March I hope) for me to work in an unheated garage, I’ll likely have 8- 9,000 miles and 5 - 6 months on the knock sensor hack before the supercharger comes off and I have access to the bad part.

As always, thank you to everyone for your comments.

Z

 

LOL! I just like to figure **** out. So Ive done some quick research on knock sensors and I am quite impressed! They are pretty neat how they are made and how they have been improved.

I have not read anything that specifically talks about a magnet near a knock sensor BUT I have read lots of descriptions which refer to a magnet located in the older piezoelectric sensors and the use of "magnetostrictive" sensors which is what I believe we have.this is a good article: https://www.apogeeweb.net/article/185.html

All the material tends to suggest a strong magnet will affect the output but to test it I would need a resonant source upwards of 7000 hz which would be a science experiment for me since I am no longer working at the place with all the test equipment I used to use. So testing one with my redneck stuff in my garage would be hit or miss.

I think we can resolve this easier by running a test. If you can hook up a code reader or SDD and look at ignition timing, see what the timing is when you first start the engine when its in open loop then see what it is when you are warmed up and take it for a drive. Lets see if the timing is advanced to the max or retarded to the max. I think it should be either or. and that will tell you if you risk detonation related piston melt. Im thinking youre retarded (lol no offense) and thats why you dont hear or see anything

 

This ignition advance is pretty close to what it is at cruising speed at a similar rpm. At idle on a warm engine it’s in the neighborhood of 0-6 degrees advanced.

Just as the Jaguar manual points out and is mentioned in a previous post, the timing is automatically retarded (from this level) when the rpm and load dramatically increases
independently from the knock sensor signals .

which is when engine knock is most likely to occur.

excuse me not taking photos of this data when the car is moving, for safety sake I have to draw the line there and give all attention to the road ahead.


Z

 

if I get a chance I will try to log some timing parameters on my STR tomorrow to compare. But with that obd connector right by my leg I imagine im gonna knock it loose driving. But I will see. I have to check the codes anyways as my check engine light came on today after changing the airfilter. Probably another small leak with that valve cover tube to the air intake tube

 

As my old Dad, a nonagenarian retired engineer said to me in my teens, ''the biggest problem with most engineers is Son, you ask them the time and they build you a watch''. As true today as it was then.

 

All speeds in km/h

Just slowly accelerating, rpm low (2,500), ignition timing moderate (25) , throttle position low (22)

Accelerating faster, throttle position (39), rpm (4,550), and speed (80 km/h), all climbing. Ignition timing(16), dropping as expected.

Acceleration slows(90 km/h), transmission shifts up, rpm decreases (3,478), throttle position closing (22), ignition timing advances (23) as expected

Acceleration continues to slow, transmission shifts up again, rpm drops more (2,033), throttle position closing more (11), ignition timing advances (33), as expected.


the above sequence took place in 2-4 seconds. I don’t see anything out of the ordinary. Traffic was moderate so couldn’t really get a “flat out” accelerating reading.

Z

 

wait.... you still have one knock sensor in the correct position, right?

Thats why this all looks normal- because the other knock sensor is doing all the work (I bet)

so with that in mind, you arent in the out if control situation I was thinking. Now if both sensors were moved and magnetized then my nightmare scenario would occur. But here, you might be having slight detonation on the bypassed bank but I bet you'd be getting close to the same on the monitored bank. so if the monitored bank picked up a knock it probably changes the timing for all the banks. And Id imagine all things being similar, a knock on the unmonitored bank would be shortly followed by one on the other bank and then the timing gets retarded.
anyways, those numbers look pretty good so something is controlling it good enough .

good luck!

 

yes, as previously mentioned, the right bank knock sensor is still in the factory position and working fine.

additionally, as you pointed out in post #12 quoted from the Jaguar manual, “.... During acceleration at critical engine speeds the ECM retards the ignition timing to prevent the onset of detonation. This action occurs independent of input from the knock sensors....”


This ECM feature, plus the remaining functional knock sensor, is my basis in fact for disregarding the likelihood of engine knock of the type severe enough to be damaging. If one has fuel of sufficient octane, engine knock at low power is not an issue in a well designed engine. But when rpm and the engine load are both high, that’s when retarding the timing can be very useful. The ECM takes care of that situation automatically with no input from the knock sensors. That’s just sensible engineering.

Z

 

Ive never looked at the timing in my STR ever but Im not sure I would expect what you showed. In my 'cuda, I set my distributor up so I get maximum advance as early as possible without detonation and I hold it there to redline. Its set for about 20 degrees initial and Im all in by 2500 rpm peaking at 34 degrees total.

I dont drop off when I floor it because it makes more power at 34 degrees total.

I wonder if you are dropping timing prematurely. IDK But Im gonna find out!

 

Of course the Jaguar has 3D maps based upon rpm/load, and then advanced software as well.

So that you see the ignition changing, is normal behavior.

Knock control was designed with that as well, nothing changes there in the risks you take.

1 Bank is still protected as the Knock sensor is in the proper place and working. the other bank obviously doesn't have knock protecting.

You will never see any ignition change based upon Knock detection via an OBD device, so no point in looking into that.

 

my intention was not to see if the knock sensors were affecting the timing. I merely wanted to confirm what I already was thinking; that the existing timing changes were sufficiently robust in their execution, to minimize any effect of the one knock sensor being relocated

I realize we are diametrically opposed in our interpretations of the data provided by the OBD-II ,

However, I am satisfied there has not been any evidence of performance drop off or knock related damage. Will continue to monitor piston(s) condition via endoscope.

thank you for you comments.


Z