My engine has the old screw-in barrel type knock sensors. Can I replace them with the new style (genuine Jaguar) doughnut sensors with addition of the studs, of course (the connectors are the same). I can see that the old style and the new style sensors have different resistances. Will this cause any issues?

 

That may depend on your year and model. If you put it in your signature, we'll know a bit more for direction.

Here's a thread to review by the well respected member jimlombardi... https://www.jaguarforums.com/forum/x...t-1-2-a-76815/
If its not in that thread, I very sure he put it in another about what your asking.

 

Thanks for the response. I have read the thread you quoted and the question on whether the old, screw-in, type can be replaced with the later doughnut type was asked but it was not answered. I have also searched everywhere and could not find the info. The Jaguar parts catalogue shows screw-in type up to VIN 853935 and the doughnut type thereafter with no differentiation between NA and SC.

My engine is 1999 SC, VIN 876481, and, according to the catalogue, should use the doughnut type knock sensors. However, the SC engines were still AJ26 up to VIN 878717, and so is mine, and my existing sensors are the screw-in type which contradicts the catalogue. I can see that the parts suppliers make a difference between NA and SC with regard to the knock sensor and specify the screw-in type for SC engines up to VIN 878717. If the parts catalogue is correct, then the doughnut type can be used on any engine from VIN VIN 853936 (NA or SC) and the fact that my post 853936 car has the screw-in type (but could also have the doughnut type according to the parts catalogue) suggests that these two types of sensors are actually interchangeable.

In view of the uncertainty about interchangeability of the two types of sensors, I am trying to find out whether anyone has actually replaced the screw-in type with doughnut without any issues. The screw-in type has 550 Kohm resistance and the doughnut 200 Kohm.

 

Why do you want to change them over?

You can test one or both - a quick check by disconnecting the old and plug in the new, then see if you get codes. I think I remember a thread about an AJ26 SC car having a 4.2 swap, there was a mention of the knock sensors...

Found it..
https://www.jaguarforums.com/forum/x...-thread-61113/

 

My old screw-in sensors are good but old. Since I had to do cylinder head work, I decided to also replace the knock sensors with new ones so I don't have to go through the trouble of removing the supercharger to replace the sensors when they fail, possibly fairly soon as they have never been changed (85k miles). So, following the parts catalogue (doughnut from VIN 853936, my car is 876481) and before I saw what type of sensors I actually have, I bought new doughnut sensors. Now, I am about to put the supercharger back in and I would like to know whether I can use the new doughnuts instead of the old screw-in types, otherwise I have to put the supercharger installation on hold until I get new screw-in type knock sensors. I read in detail the thread you provided but it does not mention whether the screw-in and doughnut sensors are interchangeable or not.

 

Oh well - having skimmed through it a couple of members advised to go with the originals, although more expensive, one of those members was on the engine design and development team at Jaguar.
The main thing would be ECU interpretation - as I suggested you can plug the ring sensors in and energize the ignition to see if they flag and immediate fault, you don't need to run the car for the ECU to run sensor signal checks, you only need to know IF they flag a fault, if they do, then AJ27 sensors don't work with AJ26 ECU architecture.

 

Keep the old school type- the car was calibrated to them and responds to knock with them.


One of the highest on my list of stupid 'internet' things that folks brag about on these cars is changing the knock sensors for the later ones.


The second one is folks that place the new knock sensor at a different location because they're too lazy to put it where it was intended, designed and tested to go.

 

Excellent idea, I didn't thing of that. I will give it a try, first with the KS-s disconnected (fault), then with the doughnuts connected and, if fault, with the original old screw-in KS-s connected. Will I have to run the scanner to see if there is fault or will the fault be displayed on the dashboard?

 

I think you are right and I have already ordered new "old style" sensors. I also found a discussion on screw-in vs. doughnut sensors on Ford Mustangs (1996 screw-in, 1999 doughnut) where it was explained:

"The donut style knock sensors have a different output than the screw in type.

Donut type are not tuned to any frequency, and the output level is about 20mv/g.

Screw in type are mechanically resonant, meaning they are tuned for a certain frequency band. The output level is about 500mv/g, or about twenty five times larger than the donut style."

Although the screw-in type for the '96 Ford may not be similar to the Jag one, it is possible that such difference also exists between the two types of the Jag knock sensors.

 

FYI:

IGNITION
Ignition Knock (Detonation) Control

AJ26

• The ECM retards ignition timing to individual cylinders
to control ignition knock (detonation) and
optimize engine power.
• Two knock sensors (KS) are positioned on the cylinder
block in the engine vee to sense engine detonation.
• One KS is positioned on A bank and the other on B
bank.
• Each knock sensor has a piezo electric sensing element
to detect broad band (2 – 20 kHz) engine
accelerations.
• If detonation is detected, between 700 and 6800
rpm, the ECM uses the crankshaft position sensor
(CKPS) signal to determine which cylinder is firing,
and retards the ignition timing for that cylinder only.
• If, on the next firing of that cylinder, the detonation
reoccurs, the ECM will further retard the ignition
timing; if the detonation does not reoccur on
the next firing, the ECM will advance the ignition
timing incrementally with each firing.
• The knock sensing ignition retard / advance process
can continue for a particular cylinder up to a
maximum retard of 9.4 degrees.
• 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.

Knock Sensors (KS) – AJ27
• The AJ27 sensors are of an annular (doughnut) construction
and are mounted via a stud and nut to the
cylinder head.
• To improve cylinder identification, particularly at
higher engine RPM, switched capacitive filters are
incorporated in the ECM.
• Knock sensing performance is further enhanced by
the use of improved ECM signal processing software.

Knock Sensing OBD Monitoring
KS sense circuit out of range (low voltage)
With the ignition switched ON, the ECM monitors the A bank KS signal for low voltage. If the signal voltage is less
than 0.6V on the first trip, the ECM takes default action. If the signal voltage is less than 0.6V on two consecutive
trips, the ECM flags a KS DTC and the CHECK ENGINE MIL is activated.
Default action: the ECM sets ignition retard to maximum.
KS sense circuit out of range (high voltage)
With the ignition switched ON, the ECM monitors the A bank KS signal for high voltage. If the signal voltage is greater
than 4.15V on the first trip, the ECM takes default action. If the signal voltage is greater than 4.15V on two
consecutive trips, the ECM flags a KS DTC and the CHECK ENGINE MIL is activated.
Default action: the ECM sets ignition retard to maximum.

 

Thanks for the info. I've now realised that this is available in the AJ26 / AJ27 Engine Management Systems training manual which I have but did not think of looking at it. So, it appears that the doughnut KS will not work (or not work properly) on the AJ26 (SC or NA) engines. The Parts Catalogue is obviously wrong when specifying sensor LCA1692AE (screw-in) up to VIN 853935 and LCA1692AE (doughnut) from VIN 853936 without reference to NA and SC. It is correct for NA engines but the cut-off point should be VIN 878717 for SC engines.