I have a '90 TPI MAP system with a weather proof Corvette ECM that has run great until recently. This system sets on the original '89 350 TPI WS6 Firebird engine that has had the harness changed and the MAF removed as well as the knock sensor and TPS changed to the MAP components. I set the initial timing @ 4 deg BTDC (with the wire disconnected). With the timing wire connected, the timing advances to approximately 10 to 12 degrees at idle. When I advance the engine speed either in neutral or driving the car, sometimes the timing advances as it should and other times it does not. It will throw a 43 code when the timing does not advance correctly. When I am driving the car you can feel the car run correctly sometimes and other times it does not because the timing will not advance correctly and it bogs down badly during this time. I have also verified my TPS voltage and it is set correctly and advances throughout the entire range correctly. The normal idle speed is approximately 750 rpm's and the O2 sensor is indicating the engine is going into the open loop correctly and stays there when the engine warms up. (This car has headers and is using a heated 3 wire O2 sensor.)

I have checked the wiring and have not found anything bad, burned, broken or lose. I also changed the ECM and prom with with spares I have and there is no improvement or change so I believe both the original ECM and prom are OK. It is my understanding the ESC is in the ECM on the MAP system so I am not clear on what might be causing my problem. Any help with this problem would be appreciated.

 

First, the correct setting for the timing is 6* BTDC on all the TPI engines. Not that that has anything to do with your code 43. The ecm sends a test signal to the knock sensor every time the ignition is cycled on. If the wrong signal or no signal is returned, the ecm defaults to a less aggresive timing table to protect the engine from detonation. You can run without the knock sensor but it means changing the settings in the prom chip to prevent the test signal from setting the code 43.

 

The initial timing is off because I dropped it to 4 deg BTDC in an effort to run 87 octane gas without the ping under heavy loading and because of the higher gas prices during the past few months. I will check the knock sensor to see if there are wiring problems. The knock sensor is about 1 year old but it could have gone bad recently.