Knock Counts Rising with the Engine Off?? 7747

[Drnhandy]

Hey guys, I'm new here and been working on trying to get a gm crate 350 that had a carburetor to run right on my 7747 ECM.

Currently I have knock counts rising in the Knock Accumulator under Running Sample Count even with the engine off and key on, knock sensor plugged in or not. This sounds to me like a software issue. The code I am getting is 43 for the knock and 51 for the prom since I have added a Moates socket booster to be able to burn chips. I am running TunerPro RT ASDU $42 with $42-1227747-V5.9.3.xdf and $42-1227747-V5.2.adx

I will also get a random number of counts when looking at the Most Recent Sample in the Knock Accumulator. It can be anywhere from zero to 17 counts. The number will stay the same for all of the boxes until I restart the truck, which then it will replicate a different number.

David

[NomakeWan]

Are you sure the knock sensor wire from the ECM harness is actually plugged into the knock sensor and not something else? Additionally, Code 43 means that the correct resistance value is not being detected (not whether or not the sensor is working), and even if you're using a socket booster I don't think you should be getting 51 unless something is really not right about your setup. Could be wrong, never worked with $42 personally, but as far as I'm aware using something like Ostrich or Romulator never throws 51 unless you have something hooked up wrong or something is loose.

[Drnhandy]

Ok so I am following what you're saying and I removed and replaced the ecm with a stock aktr 1227747 from a different truck. I'm still getting the random knocks at every rpm and map value like before. I ohmed out the knock sensor with the connector removed and it is at 100K Ohms. I this the correct knock sensor reading for my current ecm set up? What about the ICM module? Not the one on the distributor, but the one next to the egr solenoid.

Edit: Also the 51 code went away so I must have a connection issue or something with the socket booster setup.

[NomakeWan]

And you confirmed continuity between the pin on the ECM harness that is used for knock sensor input and the knock sensor pin itself? I just want to be absolutely sure that you have the wiring going into the ECM correct. If the wrong thing is plugged into the ECM's knock sensor pin, that could potentially cause all kinds of weird stuff to happen.

I am not familiar with your ECM so I don't know what resistance it expects. The expected resistance value for the knock sensor will be found in the FSM for the car the ECM came from. For example, in the FSM for the '95 Corvette, in the section for diagnosing a Code 43, the expected resistance value of a single knock sensor is between 3300 and 4500 ohms. You will need the FSM for whatever vehicle the 7747 came from to verify what resistance value it expects.

That said, the Code 43 is not actually determining whether knock is occurring or not, and has nothing to do with excessive knock. All it is doing is checking to make sure that the correct amount of resistance is found in the circuit (using a voltage divider inside the ECM to check the circuit voltage). This resistance is not inherent to the function of the knock feedback system; it is provided by resistors that GM added to the knock sensors to allow this function to work. These resistors GM added are fragile and often will fail well before the sensor itself fails. While you can of course replace the sensor to get rid of the code, disabling the code works just as well (and doesn't affect the knock feedback system one iota).

However, in this case I highly suspect that there is a wiring fault, because you are getting a Code 43 in addition to strange behavior on the knock feedback system.

[Terminal_Crazy]

Check the continuity & condition of the cable. check that it isn't frayed on body work & shorthing out anywhere. (Just because it might check out fine everytime you pull the PCM.
Mitch

[PlayingWithTBI]

What about the ICM module? Not the one on the distributor, but the one next to the egr solenoid.

That is the ESC (Electronic Spark Control) module. The KS is wired (Dark Blue) to it. The picture is for my 88 C1500 which s/b good for your 7747. Here's a link to some Service Manuals - may help
https://www.gmt400.com/threads/88-95...manuals.43575/

Another thought - maybe your KCs are coming from a loose exhaust pipe, motor mount, or something else hitting the frame?

[NomakeWan]

Oh, this model uses an external ESC?

Then you need to check continuity between the sensor and the sensor pin on the ESC, and continuity between the ESC output pin on the ESC and the ESC input pin on the ECM. Make sure everything is going to the right place. If you've wired the knock sensor directly into the ESC input pin on the ECM and your ECM is expecting only filtered input from an external ESC, that could explain things.

[Drnhandy]

Thank you all to have contributed so far, I knew you were going to help! I feel like I'm finally going to get this problem solved. I plan on checking the continuities between the KS and ESC and also ESC to ECM and related grounds. If that checks out I will be inspecting wiring for possible inductance or damage. I will probably just temp in a new wire at that point. If all of those things pass I will be replacing the ESC Module.