The knock sensor is installed in our trucks. It appears to be wired up and there is circuitry in the computer to use it. It is turned off by Ford as it has trouble distinguishing other noises and vibrations from the blower or whatever and pulls timing even when it isn't needed. Is this true?

If so, then the computer has the capability to use a knock sensor if the sensor could be trusted, right? There is a prominent company that has a unit that could go between the factory knock sensor and the computer and filter the messages and determine whether it is detonation or not and then when it is that is passed onto the computer to allow it to handle the issue. Since the main problem is in trusting the sensor, if this can make the sensor "trustworthy" then it should be a viable alternative. This system has the ability to only retard a single cylinder or cylinders that are having a problem. There isn't a sudden cutting of all power or a big delay to get it back, it is virtually instantaneous. But for it to work the circuitry must be able to be turned on in the computer through software, which I believe is available.

Any thoughts? Oh he is working on an 8 coil on plug system but he already has a simpler (and maybe less expensive) solution if the above is true.

Jody

 

A simple way is to use a stand alone system suck as "KnockLink". Very effective tool.

 

you'd have to ask one of the knowledgeable chip tuners about making use of the existing knock sensor, I believe that they can turn it on.

it seems like I remember that sal or somebody has experimented with trying to make a program that used it before.

my question is how does this aftermarket kit, make use of the existing sensor, but still filter out other noise?

my bigger question is:

how exactly does it manage to do this?

how is the existing sensor able to differentiate which cylinder(s) are having detonation?

later,
chris

 

Thanks guys. Chris, here's their explanation:

"The system does not need a cam or crankshaft reference to determine which cylinder to retard. The unit is programmed to "know" that the knocking cylinder is the one that just fired, and that it won't fire again for two more revolutions. When the knocking cylinder comes around to fire again, software dials in the retard amount for that cylinder. It does this as each cylinder goes by, building up a different retard amount for each cylinder.

The unit has a high energy ignition with constant energy dwell controller. The system monitors the coil current, and adjusts the dwell time to achieve seven amps of coil current. Compared to a GM HEI, this is a 62% increase in energy stored in the coil. The system can also be used to trigger an MSD."

They've been doing this for many years. I also want to know if the stock knock sensor will work correctly since Ford couldn't make it work. If not he is developing a system that will work on our trucks that uses his sensors.

Jody

 

I am highly skeptical that some third party can make it work when Ford could not. Detonation is the number one killer of supercharged engines. As you note, Ford already had all of the bits in place. Ford has had six years -- and a gazillion dollar tuning budget -- to implement the sensor.

I ain't a sayin' that it's impossible, but it seems like a long shot to me.

 

Could be Tim. I am very confident that his stand-alone system can do it, but it's not done yet (for the coil over plug ignition). I asked him the same thing about using the factory sensor and will post what I find out.

Jody

 

I will try my best to explain it and if I am wrong someone please correct me.

The knock sensor is a Piezo electric device that when stressed will output a voltage.

How it works:

Basically, when a ping or pre-ignition happens it creates a shockwave, or you could actually call it a frequency signal. The knock sensor will feel this shockwave or frequency wave and then depending on how strong the shockwave or frequency is the knock sensor will put out a voltage, which is usually somewhere around +/- 2 volts.

What’s important to note is the designers of the motor are going to know approx. what shockwave window or frequency window needs to be sensed by the knock sensor for it to work properly.

For arguments sake lets say when per-ignition happens it creates a frequency of 60 – 80hz. If that were the case then “anything” on the motor that creates that frequency will set off the knock sensor and retard the timing.

I have heard the reason our particular motors do not use knock sensors is because of the vibration of the blower, or the frequency that vibration creates.

So, if our motors put out a frequency of 60 – 80hz (again I have no idea what it is but just using these numbers for explanation) when pre-ignition happens then you can not have anything on the motor that puts out a frequency any greater then 60hz or the knock sensor will retard timing.

The knock sensor is a stupid device that has no idea what created the frequency, it just senses any frequency. This is why you can test to see if a knock sensor is working by lightly tapping the motor with a hammer while monitoring the timing. If the timing retards as you tap the motor with a hammer the knock sensor is working.

Now, lets assume our blowers put out a frequency of 80hz or greater. If that were true it would always activate the knock sensor. This is why I believe what I had read a few years back that our blowers create too much vibration to enable us to use the knock sensors.

You also have to remember that a knock sensor, if working correctly, is going to detect any pre-ignition before the human ear can hear it. So in other words the particular vibration threshold for the knock sensor to work is most likely not going to be felt by your hand and this is why it may be hard for people to understand how the blower could vibrate. It does, its going to have air turbulence vibration (frequency) as well as vibration (frequency) of the rotating mass from the rotors.

 

Makes sense. But I also know of several factory blown cars (Eatons included) that do use knock sensors. I would love to be able to use this system on my truck, but it obviously has to work correctly. The system I'm working with right now is the J&S system, who's had great success with their system for many years. Whether they can design one that will work correctly on our trucks is the real question. They feel they can.

Jody

 

Just something I have thought about before, maybe really naïve but anyhow…

I would think a better way of preventing pre-ignition would be to somehow monitor each individual cylinder temperature. The engines susceptibility to knock will vary as a function of fuel octane, chamber design, and other factors but in any regards I would think keeping things consistent you could come up with a safe threshold for our motors running an octane range of whatever, say 90 – 94.

If it were possible to come up with a max temperature for safety, for example 1000 degrees you could monitor each cylinder for a max temperature of 1000 degrees. Anything over that temperature would be considered unsafe and real possibility of pre-ignition occurring.

You could then either retard timing to that cylinder, not fire the next time around to air cool the cylinder, or maybe a longer duration of the fuel injector to put more fuel to the cylinder to cool it down.

You could almost look at it like a thermostat control for each cylinder. You could have a tuner tune, program your motor to react appropriately for your situation. Maybe someone can run a higher temperature before pre-ignition. You could also tune, or program what corrective action to take in the event a cylinder surpasses the desired temperature threshold.

I don’t know, maybe not the best idea but I think, if it were possible, a much better and more precise way of controlling pre-ignition and a great safety device. Worse case scenario is if cylinder temperatures are not reacting to the corrective actions then the motor goes into safe mode, firing every other cylinder like when the computer senses the motor over heating.