Well, the new motor is together and running now. (mods in sig) Only problem I'm having is a Code 43. Start car, runs for a 20-30 seconds and then SES comes on. Check codes and its #43. I'm not sure if the knock sensor is bad or if its picking up fake knock from my one LT header tapping the k-member. I've got a scanner tonight that I'm gonna plug in and see whats up. Also, if I unplug the thing and start it, it does the EXACT same thing. Thats why I'm wondering if the sensor is bad. One other question, can I use my knock sensor from my 305? Someone said no... why not?

*How exactly does the knock sensor work? Is it always sending voltage or a signal to the ECM or just when its sensing knock? I'm not to familiar with this circuit.


THANKS ALOT for any help!

 

The knock sensor is a piezo-electric microphone. And just like a piezo-electric tweeter that you'd find in a speaker, it is tuned to only pick up (output in a speakers case but you know what i mean ) certain frequencies. Engine knock makes a different frequency hit depending on the size of the bore it's happening in (just like different size cymblas will make different crash noises for drums), and that is why they are different for 305s and 350s.

As for it's actual operation, the ECM sends a constant voltage signal to the KS. When the KS 'hears' a certain frequency, the microphone will vibrate, which causes a variation on the voltage from the ECM, which the ECM detects via the ESC module (which is also specific to 305 / 350, just like the noise coming from the engine varies with bore, so does the 'noise' the KS makes on the wire vary with the sound it is picking up. Think of if you send bass to a tweeter, nothing comes out. Same thing but backwards for the KS - ESC talking to each other, the ESC is tuned for the same frequency that the KS hears) Now granted it's not as extreme as the difference in sending bass to a tweeter, but they are different enough to matter if you're looking for accuracy.

I don't think using the wrong sensor / ESC would necessarily give you a code 43 though, lots of people do it all the time. It could be from the header hitting the k-member. Header leaks, loose brakctes and other tapping noises have been known to cause problems on the KS.

Or it could be the sensor or ESC itself is bad, which seems more likely since the ECM seems to notice it immediately. You can at least isolate if it's the sensor or false knock by bypassing the KS with a3.9k ohm resistor. If that fixes the problem then you know the ESC is good at least and can then try to determine if it is false knock from the header banging. Unless the banging is nearly constant though, i would tend to think the sensor has just gone bad on you. Maybe try making a torque strap to tie the engine down hard in the mounts to keep the header from hitting and see if that fixes it though if you're uncomfortable replacing a part without completely verifying it is the cause. Also of note is that if the wire to the KS is grounding somwhere (maybe burnt on the header for example) that could be causing your problem. Worth making sure you have 5V at the sensor connector to check that.

 

Thanks Ed! I got a Monitor 4000E scanner and was checking stuff last night. Its getting code 43.... ESC FAILURE. Its picking up0 no signal from the KS though. I think thats good though. Its not picking anything up from the headers though! I'm gonna disconnect the KS and see what the scanner says 2nite. If it does the same thing, I'm gonna replace the KS and hopefully that fixes it. As for everything else, I guess its ok. BTW- Is there a ESC controller or module? Where's that at? Thanks for all the help Ed.


*A few wuick other questions. What should my IAC, inj. PW, spark advance, and knock retard at idle be? Just wondering know that I can check them with this scanner. Also, its running like 17-20* advance at idle with about 6-8* knock retard. Is this about right or totally wrong? ALso when I drove it, at about 2500-3000 rpms, it had a out 38-40* advance but had almost 20* knock retard. Is this right or wrong also? I don't know where to go with half this info. Thanks!

 

Ed, you still here??????

 

Just buy a 4th gen. and mod it like crazy!

j/j Hurry up and break that thing in so we can see what it can do. Makes me want to hurry up and get mine done.

 

Yeah Rick! You better get that motor done too!


As for my car... all it was was my knock sensor. Tested my KS and it didn't have any resistance. I put my old 305 one in and it works fine. The knock retard I was getting b4 for no apparant reason is gone too! I guess the ECM retarded the timing b/c it knew that the KS wasn't working. Does this make sense to anyone?? Well, thats it.

BTW-The GM tech manual I used said the KS should have like 3000-5000 ohms resistance and should have 4-6 volts going to it from the ECM. Thats it, later