Flat Response Knock Sensors - Not all are created equal.
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- Опубликовано: 12 сен 2014
- A guy named Kurt made a post (www.efi101.com/forum/viewtopic...) detailing resonant response and flat response knock sensors, how to detect knock (ping, detonation, etc) and setup the AEM EMS optimally for knock detection/correction. Following his post, I installed a flat-response knock sensor on my engine.
The one I bought originally was a cheapo generic sensor from eBay and it worked okay but had too much noise on it. After a quick discussion with Kurt on the AEM forum, we came to the conclusion that the knock sensor was grounded to the block. This is horrible, because wiring that sensor to the "sensor ground" on the EMS will contaminate all my sensor readings!
I then ordered the authentic Bosch sensor (part# 0 261 231 006). I found that it was exactly what I needed and the best part was that the pigtail I bought with the generic sensor fit on the Bosch one!
If you are not aware of "chassis ground" vs. "sensor ground" when handling automotive electrical systems, read this article from the megasquirt website regarding grounding and it'll all be clear: www.msextra.com/doc/general/gr...
This guy is right a grounded ring sensor is undesirable unless yours is specifically a one wire type. mine showed resistance to ground & was faulty, the new working 2 wire sensor was not grounded
The important thing to do is to not make a mistake with the wiring polarity. If you switch GND with signal you will get spikes going into the ecu. We use both sensors on Tuner Nerd Knock monitor pro. The Bosch gave a slightly flatter response and the polarity can be switched. The nissan style sensor gives a good response too, but dare you not switch the polarity!
TLDR: Buy the bosch - they work everywhere , but the internally grounded sensors are good for systems configured for it.
Aren’t nissan knock sensors designed that way ? The ground to the block from factory
I'm not saying your solution of a floating sensor will not break up a ground loop, it will, but the system description is not accurate.
Most sensors are mounted to the block, directly or indirectly. Water temperature, manifold temperature, oxygen, and even the Ford TFI PIP system is block centric. Ford, as one example, directly grounds the PIP to the distributor and the block. Because of this, many factory systems use a block-centric sensor ground system. They do this to prevent ground loops.
The real issue comes in with aftermarket manufacturers. For some odd reason aftermarket manufacturer's often tell people to ground to the worse possible place for noise and safety, the negative battery terminal. That ground is usually unfused, and goes to a common bus inside the aftermarket electronics that is shared with sensors and other pickups. This is the real recipe for noise ingress, because the power ground loops noisy battery return current to the aftermarket equipment internal bus. That noise current loops out on a sensor ground if the sensor has a block ground or chassis ground. This is really what causes the issue.
Battery post grounds are also bad for safety. If the battery ground develops a poor connection battery negative current, which includes alternator and starter currents, will route normal battery ground currents out through the aftermarket gear's internal negative bus to whatever ground it can find on that device.
Using the Ford EEC IV as an example, Ford common grounds the PIP signal at the distributor to the block. They do this because the distributor is point where spark noise concentrates, thus they want the lowest possible impedance to the common ground at that area. They run the PIP signal at the EEC in differential, floating from ground. This prevents a low impedance ground loop, since the "ground return" is in differential with the hot PIP wire at the EEC input. The EEC is grounded to the chassis for low level and operating currents, the high current injector and solenoid return is grounded to the chassis near the battery before branching to the battery negative connector terminal. They do this because the injector and solenoids have backpulse noise and also draw considerable current. This is the same reason they did not trigger spark in the EEC, but trigger a remote module. (GM does the same.)
The only battery post connection is through a heavy cable to the block, which is common to starter and alternator, and a smaller wire to chassis which is the normal "clean" ground used for sensitive equipment not engine or transmission related. Lights, the radio, the EEC power, and all accessories are chassis centric.
There are some variations to this system, but the dumbest thing in the world is using a battery post connection for accessory device negative power unless that negative is fully isolated and the connecting wire is fused at the battery. Grounding to the battery is noise and damage waiting to happen.
hi , I have Hyundai accent. 96 models. knock sensor in my car with 3 plugs( not 2 plugs.) how can I check this. Thanks...
The series 2 I have has one pin for the knock. I get you aren't grounding the second knock sensor wire to the engine, where did you connect the second knock sensor wire?
Im working on a maxima and wondering the same...I bought a a sensor and wire harness off ebay for 30 bucks which said oem with nissan packaging but no writing on the sensor, harness has two wires going down to one wire at the sensor plug , I need to test tp make sure cause I'm having issues
Some knock sensors have 2 pins but on have 1 wire on the connector plug... So have to use the engine as a ground.
It looks exactly the same as the on in your video... :) Not sure what flat response it.
Nice informative video, just a question about the bosch knock sensor, which pin is signal and which is meant to ground at the sensor ground? or does it not simply matter? cheers.
+Sefveron : hi, thanks for the response. I don't believe that the polarity of the sensor is important. The sensor is really just a microphone and will create sinusoidal waves across the two pins when it experiences vibration. You can test it by lightly tapping it while it is hooked to the DMM or to amplified headphones.
+Greg Grotsky cheers!
I relocated my 2002 Nissan Xterra knock sensor and code still comes up ????
I'm sorry, but your opinion cost me more than $250. Unfortunately all of the sensors (old one, ebay $9.and oem one) do have ground!! Please redo your experiment.
mohamed alromaithi this is not an experiment nor my opinion, I am showing you what I found when I purchased a knock sensor from eBay. There may be eBay knock sensors that don't have their electrical pins shorted to the body of the sensor but I know from these measurements that the Bosch sensor does not.
Nissan use the engine block to ground the knock sensor and the plug from the engine wiring only use 1 wire for the signal, its is 100% same as your ebay generic sensor
it depends on the manufacturer... some will ground thru the block and some will not.. he only told u what his experience was..its not universally that way across the board