got a code 43 on startup

[bigunde]

Just rebuilt the engine in my 94 and i get a check engine light and code 43 soon as its started.any ideas?

[ChevyTech]

I would clear the code several times and pay attention to exactly when the code sets. Is the self test criteria met?

CODE 43

Each time the Vehicle is started and certain criteria is met (coolant temp, MAP reading, engine RPM), a self test of the knock senor circuit is run. The ECM adds spark advance while anticipating a knock signal. If not knock signal is detected during the test a code 43 will be set. Some GM manuals state that two consecutive tests must fail for a code to set. (All GM electronic spark timing systems are not the same. Some systems use a separate module between the knock sensor and computer)

The self test is not the only condition that will set a code 43.

Anything that prevents the knock/ping or prevents the system from detecting it will cause a code 43 to be set. A bad knock sensor, ECM failure, wiring, Timing way retarded or a very rich mixture can cause the code.

The Knock sensor contains a piezoelectric crystal which causes a voltage to be produced. Loose components on or in the engine can cause the knock sensor to create a voltage and the system may interpret this as pinging.

Loose torque converter bolts can cause a false knock signal to be detected.

Knock sensors are more fragile than they look. I like to only tighten them by the hex on the base on the sensor, not by the hex on the plug eng of the sensor.

Did you use Teflon tape on the knock sensor? It has to have a good electrical connection to the block.


Here is an article I found some time ago when looking for web site information to send people to:

Chevy Pickups With The "Mysterious Code 43"
It’s not uncommon for Chevy pickups with injected 350s to set a Code 43 indicating erratic spark or a detonation problem after the installation of a remanufactured engine. The installer usually blames it on the engine because it has "the wrong heads" or "the wrong compression ratio" after everything else seemingly checks out okay.

Rebuilder’s survival tip: The main wiring harness runs along the right valve cover. It has a "dip" in it that is supposed to go under the heater hose. If the installer turns the harness upside down so the "dip" goes over the heater hose, the harness is close to the plug wires and it will induce a small current into the harness when the engine is run hard.
This small voltage in the circuit for the knock sensor is all it takes for the computer to "think" that there’s erratic spark or detonation present, even though there really isn’t a problem, so it sets a "Code 43" after a road test. The computer always checks the spark control circuit at start-up and sets a Code 43 if there’s a problem in the electronic spark control circuit, but it should never set a Code 43 after it’s been running down the road. If it does, then you’ve got the "Mysterious Code 43" that is probably caused by the high voltage plug wires inducing a current into the harness. We have fixed several of these pickups with this problem by rerouting the harness under the heater hose.

[bigunde]

I need to get a timing gun back on that rascal if i can remember which wire to disconnect.i pulled the timing up a hair and the light didnt come on until i reved it up some

[ChevyTech]

On 1994s the set timing wire is inside the cab on the passenger side.

Check for anything that could rattle and set a false code.