Hi everyone. I am new to the forum. I have been following along for awhile, and there is lots of good info. here. I have a 1985 4+3. I keep getting code 43. Set base timing ( with est conn. disconected) to 6 degrees. Replaced knock sensor. No change. Checked all wiring. Seems to be okay (all conn. at sensor, esc, ecm, & good ground). The sensor (old one & new one) reads a resistance of 100k ohms. Does anyone know if I can replace the sensor with a 100k ohm resistor to ground to make sure the esc and ecm are operating properly. Thanks in advance for any info.

 

Dan,
I just went through the same thing with my '92 LT1. After replacing the sensors, I kept getting a code 43. I cut the wire leading from the ecm and replaced it with appropriate resistors to ground - still got a code 43. That was the evidence I needed to replace the ecm. Upon replacing the ecm, the system works fine. A rebuilt ecm cost $100 (plus a core charge of $125)from mid-america. Good luck.

 

I have an 86 and I by-passed my knock sensor a few weeks back by using a 4.7K ohn 1/4 watt resistor. Got mine from Fry's Electronics.

I completely eliminated all knock retard as verified by Diacom.

Here's what I did:

Found the wire that leads from the knock sensor to the ESC module. In my case the wire color was BLUE.

I cut that wire and soldered in one end of the resistor to the wire leading to the module. At the other end of the resistor wire, I soldered on a length of insulated wire I had laying around in the garage. I then ran that end of the insulated wire to a ground location.

I used a chassis ground at the spot the hood latch is located on the passenger side of the engine compartment.

I capped off the other end of the BLUE wire ( that leads to the knock sensor).

I used cable ties/wire ties to secure the wires and slid a piece of corrugated plastic, wire loom covering over my handiwork.

If I remember correctly, there are three or four wires leading to the ESC module and in my year, BLUE was the color. I found the correct wire by referencing a GM Shop Manual. Check to make sure you get the correct wire color.

Now, when I start the engine, the resistor provides the necessary resistance the ECM is looking for. I get one, that's 1, knock count only. Engine pinged at various throttle positions, so I just backed off the initial timing til there was none.

BTW the manual calls for 14 ft. lbs (GM wasn't using lbs./ft back then) of torque on the sensor; don't tighten it more or if may become too sensitive. It also says to use sealant tape on the threads to prevent coolant leaks.

Hope this helps.

Jake

 

Thanks for the replies Jake & Mtvette. So I assume I am right about the resistor being a way to eliminate the possibility of exhaust noise, loose brackets, or maybe even real knock. If the esc & ecm are ok with the resistor you should fool the computer and have no code 43. I tried the resistor and still got the code. I installed a new esc and still got code 43. I guess the next thing is the ecm. Does anyone have pro or cons about using parts from places like Advance or AutoZone? I can get the ecm from them faster than I can get an AC/Delco. Thanks again.

 

If you are going to replace the knock sensor do not add sealant to the threads of the knock sensor the sensors are signal wire sensor which means it has to ground to the block so if there is too much sealiant on the threads it can keep the sensor from working correctly and give you a code 43. I assume you must be seting the code while driving and going to near WOT when the codes sets, if this is the case then it is failing the performance test which is that when after the coolant gets above I think 190 deg. and you go to near WOT the ECM will add extra timing into the distributor then look to see if there is any spark knock, if it does things go back to normal if not then a code 43 will set and timing will be kept retarted untill the key is turned off. There are a few things that can cause this problem.
1- to high of octain fuel (so it is unable to knock with the added advance)
2- excessive sealiant on the threads of the knock sensor
3- overtightened sensor that has made the sensor inop.
4- poor terminal connection at the knock sensor(a real problem with the LT1s)
5-High resistance in wire going from the sensor to the EST modual
6- ECM (probably not likely)
7- EST modual (again most likely not)

Get a timing light and a friend start the car get it warm with the timing light on have someone hold the idle at about 2000 rpms and watching the timing mark while the other with a long pipe on top of one of the head bolts tap it wilt a hammer to simulate spark knock and the timing should retard, this is just a quick test if it doesn't that proves the cause but you could still have a problem and see the timing drop next would be to go to the EST modual unplug the connector and I think Jake is correct that it is the blue wire and check the resistance to groung it should be the same as it was at the sensor if not the problem is in the wire coming from the sensor (most likely the problem) the wire comes up the rear of the engine and real close to the exhaust manifold an that can sometimes cause problems with the wire, replace the wire and recheck. Now if the resistance is correct what kind of fuel are you using 93? if so try increasing ign. timing with the higher octain fuel in might not be knocking while testing but do some checks and let us know.

David Fulcher