No announcement yet.

Knock Sensors, don't waste your time

  • Filter
  • Time
  • Show
Clear All
new posts

  • Knock Sensors, don't waste your time

    I have noticed some posts on knock sensors. I am here to tell you don't waste your time or money.

    Most of you are using the 7747 ECM which the knock sensor is made for the Chevrolet engine. These knock sensors are very crude and for the most part are a pain on the Chevy engines as well as on other engines.

    These sensors can be tricked a lot by other noises in the engine like timing chains, timimg gears, lifter noise and a variety of other noises that can be emmitted in an engine.

    Hours and hours of development with very sophisticated equipment go into the placement of a knock sensor. To just put in a knock sensor into another engine you have no idea of what noises it will pick up or if it will pick up anything at all.

    Another thing to think about is why they have them. Remeber the Auto companies are making thousands and millions of vehicles with the same engine and calibration. They cannot however predict everything that will happen. They also use a method to improve fuel economy called lean cruise or what you may have heard "highway mode". This mode is now illegal by edict from the EPA but was used back in the 7747 days.

    This strategy would lean the fuel out in open loop and add more spark under constant speed cruise conditions. Well if it was a real hot day, the A/C is on, there is a boat being towed behind the vehicle and Bubba just bought a tank of panther piss in the hills they need to insure that they don't blow up the engine under these conditions due to oversparking the engine. Remeber there is no ACT sensor to adjust the spark curve.

    Another thing to remember is that the Auto companies have fuel economy requirements to meet. If by putting the sensor on there they add .1 or .2 mpg when multiplied by their entire fleet it makes a big difference. By adding the knock sensor they may get a little aggressive on their spark and let the sensor take care of it in some extreme conditions. They don't work real well on engines that have a lot of miles on them though.

    So here is the bottom line, use the knock sensor if you want. What you can gain out of them is almost nothing and what it costs to install them is even more. The 7747 requires the sensor ($65) the module ($100) and the proper placement to have them work properly.

    I know that Ragged on eBay sells them for much less but use at your own risk. What you will gain from them is almost nothing and the cost will be much more than you will ever save.

  • #2
    So what to do if we are using the 7747? At this point I will believe anything that anyone says that seems to be within reason. I know my poor little 2.8 in my S-15 would not be long for this world if it were not for the knock sensor. Please provide more info and what to if we are using the 7747. What ecm do you reccomend that does not use a knock sensor or is it an input you can program out. Thanks for the info!!!! More lost by the minute!!!
    My "Disasterpiece"
    1970 800A 4X4,HFI'd,304,B/W,27,44,3:73,28's.
    The rest are in my 25 year plan!

    My "Ruedh"
    FREE 1972 1110 4x4,V8(?)727,205,44 drum/60/3.54's,small cheap tires.
    LOOOOADS-O-RUST!! Donor body located. Not!! JY owner played the "crusher value" card. : angry:
    NON-working rear window. Need info!!!


    • #3
      Cal out Knock sensor

      The knock sensor can be cal'd out on the chip. If you are making your own chips I can tell you how to do it.


      • #4

        Armed with the info on knock sensors from the FAQ page on your site, I entered quite a debate with a couple of my buddies that are running TBI's on their rock crawlers.

        I kept reminding them that they are both running GM based V6's that had a factory location for the sensor and stressed that I'm certain their roller cammed and roller valve trained engines make far fewer noises than my high mile 304 International.

        To appease them (I suppose) I went ahead and picked up a knock sensor while collecting parts. Like Binderman, I'm new to FI. I'd like to keep the conversion as simple as possible. I've read all the posts about programming chips, etc. and it gets way beyond my capabilities. I'm just after a reliable alternative to my carb set up. If, in the process, I pick up some extra MPG, that would be real welcomed, too.

        You've convinced me to leave the knock sensor out, not only because, as you put it, I just don't need it, but it also makes the conversion that much simpler. Heck, I had enough trouble just completing the Duraspark conversion. What is that tag that Possum Scout uses..."When in doubt - Rip it out".

        Thanks for your input.


        • #5
          One thing you will find is all kinds of experts or people who think they are who are more than willing to give you their opinion.

          Like I said in my post, if you want to use them and it gives you a warm fuzzy using it go ahead. If you are using a stock chip you will have to use it and a VSS or your check engine light will come on.

          Bottom line, not needed and the benefits are not there unless you need to get that .1 or .2 mpg better fuel economy and that is maybe. If someone wants to get real aggressive with a calibration and can find a location that they believe is working it may increase fuel economy a bit more. But also think of this, the Big Blocks, at least the late 80's and 90's models, don't use them.

          Knock sensor technology has come a long way. Many of your newer production vehicles use what is called a fully active knock sensor. This requires very complicated software and very expensive, in some cases dual knock sensors.

          These units actually add spark to the engine going down the road up to a predetermined amount until it senses knock; it then backs it off. This allows optimum fuel economy and performance from your engine under all conditions. So when it is damp and cool outside it will add a lot more. If if is hot and dry it will probably be pulling spark out all the time.

          These like I said though have very sophisticated software operating them, unbelievable filters that work well to even filter out lifter noise and are very expensive to the system. The auto companies need to do whatever they can to get CAFE up now even if it is 10th's of an MPG.

          I just got off the phone with a guy who is having the issue I talked about with false retard and it is costing him fuel eocnomy.


          • #6
            "people who think they are who are more than willing to give you their opinion.
            Like I said in my post, if you want to use them and it gives you a warm fuzzy using it go ahead. "

            This would be me.
            I still use them and it gives me a warm and fuzzy.
            Since I play with the timing on the chip, it makes me feel better to run one.
            The IH does have a location the same as the SBC donor, just in front of the starter.
            When I have my chip where I want it then I can eliminate the need for the sensor.

            When the lifters start to clatter it will give a false reading as it would on any motor.
            Might be a good excuse to do a rebuild!!!!
            Bill USN-1

            May be the answer to all your fuel injection needs!
            Learn to do it right.


            • #7
              Don't take me out of context Bill!! hahaha.

              Like I said you can find all kinds of people who claim to be experts and are more than willing to give you their opinion. You should answer my phone sometimes and read some of the emails that I get!!!

              One thing about spark knock is that there are about 3 degrees of preignition before it is audible. That is why I discussed location of knock sensors is a very in depth procedure with very sophisticated equipment. Knock sensors on other engines may in fact be getting several degrees of preignition before the knock sensor is actually picking it up. Chevrolet engines have cast block and aluminum manifold which has a different resonance than other engines do. Also an early Chevrolet engine has more cast iron in the block than the newer ones do; this also creates a different resonance.

              Bill you are building your own chips and know what you are doing. You are actually using yours to build a calibration which is great. The reason that I wrote this thread is so that people do not go out of their way spending a bunch of money that they do not need to spend.

              I am glad that I have got all of you thinking about this. It is very good to get you thinking about fuel injection, how it works and what some of the critical components of the system are.

              In 24 years of developing these systems and having gone through the process of knock sensor placement, even on very similar engines, you would be shocked to see the difference.


              • #8
                I think I fit your description pretty good. :)

                What about mixing and matching knock sensors and ESC from different motors.
                Are the knock sensors made at different sensitivity or different resonant freq for each motor?
                Bill USN-1

                May be the answer to all your fuel injection needs!
                Learn to do it right.


                • #9
                  No they are generic to the model year and the sensors are the same. What differs in sensors is software used to filter the spark knock from the engine noises and the quality of the sensor. The older ones like I have said are not as accurate as the ones they use today and the software is not as sophisticated.

                  Keep using yours, it is at least an indication that something is happening that should not be happening, to be safe though I would back off a couple of degrees to insure no knock at all.

                  By the way even todays knock sensors cannot accurately do much above about 4,000 RPM's and nothing above 5,000 so you can imagine what is happening with the older ones. This brings me back to my original point that you may not be reading spark knock all the time.

                  Confused? That is why I don't bother with them, to much false retard.


                  • #10
                    4,000 RPM? 5,000 RPM? Shouldn't be a problem with a stock International. Sorry Norm, just couldn't resist. I've never pushed my 304 looking for a limit but I don't recall ever seeing the tach wind past about 3200 RPM.

                    My buddies are still convinced that the knock sensor is the only thing that will keep them from grenading their engines. But, you've given me several reasons not to use one; less $$$ (I like that part), less work to set up (I really like that), and a good source of endless debating material when they see me running without one (priceless).


                    • #11
                      No problem, like I said previously if someone wants to use one then use it. We are Affordable Fuel Injection and I am trying to keep it that way for people.

                      4,000 RPM is only on the newer ones, the older ones I am not totally sure but I know it is not 4,000 RPM.


                      • #12
                        Re: Knock Sensors, don't waste your time

                        Bringing this back from 2003..

                        Looks like Norm isn't in favor of the knock sensor.

                        Bill notes that GM installed 'em just in front of the starter.

                        Bill - what/where do you actually mount your sensor?

                        I have one - bought a whole pile of sensors - and just don't know if it's worth the time to install it.

                        d'oh.. next thread I was reading, from Bill, in 2004..

                        No mystery.
                        It goes in almost the same spot as the original SBC.
                        passenger side of the block in front of the starter.
                        pull the block drain(after you drain the radiator)
                        then screw it in. It's even the right threads.
                        So it goes into the water jacket..

                        Are you still relatively satisfied you're getting "good" knock data, Bill?


                        • #13
                          Re: Knock Sensors, don't waste your time

                          I am pretty happy with it.
                          But since this early discussion i have found a way to bypass the knock circuit with out needing any chip reprogramming.
                          I added it to the wiring details in the sticky.

                          I would agree with Norm that engine noise is a major factor in false knock.
                          If you have an IH that rattles or has lifter noise, you will get false knock.
                          Header noise can also play a part.

                          All of these will cause the timing to be retarded and a loss of power and economy.
                          It doesn't last forever. it just reduces the timing until it quits pinging(or the valve stops ticking).

                          The choice is yours.
                          You can install it then if you feel like it's affecting your motor, then just unplug the ESC and add the little scotch lock between the 2 wires listed!!!
                          Done. 2 min work and no programming.
                          Bill USN-1

                          HAMILTON FUEL INJECTION
                          May be the answer to all your fuel injection needs!
                          Learn to do it right.