Need Help With A Trouble Code 43 On My 88 Pickup

[iridevictory]

My 88 Chevy 2500 4x4 pickup keeps getting a 43 trouble code. After doing some research I found that it has to do with the knock sensor or the electronic spark control. I have replaced the knock sensor and it is still doing it. The distributor was recently redone with new components. I know the engine is not knocking, it has only 40,000 miles on it. Can anyone tell me does my truck have a electronic spark control unit or is it a circuit in the ECM? Can anyone help me? Thanks, Tony

[ChevyTech]

Hi and welcome to the board.

Code 43 can be the hardest code to find the cause of. My first suggestion is to pay attention to when the code gets set. In diagnosing the cause, it is very helpful to know if the code 43 is being set during the self test, or does it get set driving down the road on acceleration when the system is seeing a ping or something rattling on the engine.

If I remember correctly I believe your 1988 has a spark control module that is separate from the ECM.


Here is a little info:
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)

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.


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.

[iridevictory]

Chevytech, Thanks for the info, thats some interesting stuff!! My problem started within the last 10,000 miles and seems to be getting worse. It happens apon excelleration when the engine is warm. I have noticed it more with the A/C on or when pulling a trailer. I need to look at my wiring harness, this could be my problem. I had a harness fire at one time. I'm not sure if it is the same one or not.

[ChevyTech]

It happens apon excelleration when the engine is warm. I have noticed it more with the A/C on or when pulling a trailer.

It sounds like the knock sensor is working ok but the system is no able to stop the ping.

Here are a few possibilities:
Timing not set correctly.

EGR not working correctly.

Running to hot.

Carbon buildup in combustion chambers. Here are some things that can cause more carbon:
A rich mixture, bad water temp sensor for ECM, thermostat that opens before engine reaches 195 degrees.

If it does have carbon buildup, I like using SEAFOAM or GMs TOP ENGINE CLEANER to remove it.

Does your truck have a 305?

[iridevictory]

It has a new EGR valve, less that a year old because I was getting a EGR code. I just put a new thermostat in and I flushed the radiator because it was getting hot. That problem seems to be fixed now and thermostat is opening properly. I don't think it's carbon buildup but I will try the Seafoam because I haven't put any injector cleaner in it for a while. The engine is a 350.

[ChevyTech]

Glad to here the problem seems to be fixed.

When I use SEAFOAM for removing carbon I pour it slowly down the bore of the TBI rather then putting it in the gas tank. Being your truck was running hot, it should have little carbon if any.