Code 43 on TPI

Shannen Durphey shannen at grolen.com
Thu May 25 08:37:41 GMT 2000


Hi, Mike.  I don't have a 90 manual here, but code 43 is usually
caused by incorrect resistance in the knock sensor circuit, by the ecm
failing to detect knock during the self test, or by the ecm detecting
continous knock.  Incorrect resistance can be caused by an
intermittent short to ground or open wire, which can be from bad
terminals or crimp connections.  During the self test the ecm advances
timing and attempts to detect knock.  If the knock sensor doesn't send
a knock signal back, the CEL is illuminated.  Part of the test is to
use a hammer and rap on the side of the block while watching the scan
tool for displayed knock.  You should also be able to see this in the
timing light, as the ecm will retard timing when knock is detected.

IIRC, the knock sensor line measures 2.5V with the sensor connected,
and the knock sensor output is an ac signal on top of that.  If your
knock sensor wire is too close to plug wires or another good source of
induction, it can show an a/c voltage that the ecm will think is
knock.  With a scope or DVOM set to a/c volts you'll be able to see
this.

You can install a fixed resistor in place of the knock sensor and see
if a scantool still shows knock.  You can connect a DVOM or a scope
(this would be really nice) to the k/s circuit and watch for a false
knock signal. Check the ecm pin and the KS terminal for proper
sizing.  If you are really curious, you can connect an audio
amplifier's input line to the k/s and drive around listening to the
engine the way the sensor hears it.  

But all bets are off if you are getting audible knock all the time. 
This will also set a code 43, but the cure is not in the electrical
side of things...
Shannen
mike.hoenes at ncmail.net wrote:
> 
> HELP!!
> I have a TPI system on a 350 that has been running fine for about six months. Its basically a 90 IROC setup
> with a MAP system. I am running a Painless harness.
> For some unknown reason the computer started setting a Code 43 - which is a problem in the Knock Sensor
> circuit. I have checked all the voltages indicated in the diagnostics, from  startup, running, etc, checked
> continuity and all the variables possible. I have replaced the knock sensor , the Cal pack and the ECM. I still
> get a CODE 43. If thats not enough, i have checked the timing while running and it does not seem to be affected
> - that is it looks like it is getting the same advance as it was without the code being set. Nothing else seems
> to have changed. I am out of possibilities. Can anyone offer me assistance. TIA
> 
> mike
> 
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