Knock Sensor for 4.0L HO

[CobraMarty]

Our engines don't have a knock sensor. Jeep must have felt that if they set up the ECU with a mild/'retarded' timing curve, you can run regular gas and not even need a knock sensor. That is probably why when advancing the timing with the CPS mod, the 4.0 runs better and more efficient. So what to do?

I bought and plan to install this standalone knock sensor and warning light.

http://www.viatrack.ca/

Does anyone have any experience with this or any ideas? Thanks.

 

[seanyb505]

Looks like you need something that you can run it through (megasquirt), otherwise you just get a warning light about knock and have no actual control over timing.

 

[Talyn]

Thats not a bad price even if you just get a light.

 

[CobraMarty]

Looks like you need something that you can run it through (megasquirt), otherwise you just get a warning light about knock and have no actual control over timing.

You're right, but a warning light is better than nothing.

 

[CobraMarty]

This one for $20 more (+$49.99) has 0-5v analog output to go to a gauge or fuel management/AEM FIC, etc. I ordered one of these to test.

http://www.ebay.com/itm/Knock-gauge-for-detonation-sensor-klopfsensor-NEW?item=110818862446&cmd=ViewItem&_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D2%26po%3DLVI%26ps%3D63%26clkid%3D8284342485020348146

 

[Talyn]

Estimated between Fri. Jun. 1 and Thu. Jun. 14

Not sure about that one. Service, well, good luck.

 

[O-Gauge Steamer]

For a cheap and dirty setup, the Knochsense is not bad. I have been looking at systems that run on the laptop and are "intelligent" inasmuch as they learn the normal noises the engine makes.

A tad more pricey though which is holding me back.

Here is an example of a system with filters. You can use the audio out to a laptop that has a MIC input/
http://finelineimports.net/index.php?main_page=product_info&cPath=1_6_194&products_id=739

Here is another system that can be found on Amazon:
http://www.phormula.co.uk/KnockMonitor-KS-4.aspx

But as is the case with evrything, you generally get what you pay for...

 

[Dr. Dyno]

Our engines don't have a knock sensor. Jeep must have felt that if they set up the ECU with a mild/'retarded' timing curve, you can run regular gas and not even need a knock sensor.

Actually the camshaft in the 4.0 HO engine was installed 8 degrees retarded in the '91-'95 version and 7 degrees retarded in the '96-'04. As a result, the intake valve opening/closing events occurred late thereby reducing dynamic CR and allowing the engine to run on 87 octane without a knock sensor.

 

[cruiser54]

Actually the camshaft in the 4.0 HO engine was installed 8 degrees retarded in the '91-'95 version and 7 degrees retarded in the '96-'04. As a result, the intake valve opening/closing events occurred late thereby reducing dynamic CR and allowing the engine to run on 87 octane without a knock sensor.

Built-in EGR.

 

[Talyn]

I've heard that roller rockers can interfere with a knock sensor as well as cams with fast ramp rates, such as the Comp Cams commonly used.

 

[cruiser54]

I've heard that roller rockers can interfere with a knock sensor as well as cams with fast ramp rates, such as the Comp Cams commonly used.

Good possibility. With my DRB hooked up on my Renix, I can tap the intake manifold with a large wrench and watch the knock sensor respond.

I had a knock sensor set-up with narrow band O2 sensor readout and a display for how many degrees of timing were being pulled back on my supercharged Miata. It wired into the cam/timing sensor. But that was pre-OBD-1.

 

[O-Gauge Steamer]

All of this "it picks up stray noise as a knock" conversation is why you need, IMO, a high end system to use for tuning purposes. The need is there to filter out the "normal" noise that the engine makes.

For the math inclined, here are the formulas to use to determine the frequency of the knock sound:
Knock Resonant Frequency kHz = 1800 / (3.14 * piston diameter mm)
2nd Harmonic Knock Resonant Frequency kHz = 3600 / (3.14 * piston diameter mm)

It is worth noting that on a "modern" engine, the second formula should be used.

3600/(3.14*98.9 mm)= 11.592485493292459088186613255363 kHz signal. In round numbers that is... Which, if you think about it, feels about right for the knock sound.

So, this is the frequency the system should be listening for in a 4.0L Stroker values are different, just apply your bore size to the problem.

 

[CobraMarty]

That is right, The Knock Sensor seller asked for the bore sise so he could tune it. There is also a small pot to make adjustments.

 

[O-Gauge Steamer]

But, of course I'm right...

No, just kidding. The problem with any non-tunable system will be the false triggers as the frequency of the knock is completely piston diameter based.

Personally, I am loking at the KS-4. But, I can stay conservative on the ignition for a long time at the price of the thing.