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Marc Haibeck · 07-05-2020

It looks like everybody's ideas are heading in the same general direction. If the ECM blinks a code 12 it means that the ECM has passed the power up self test. That suggests a good ECM.

Is the chip adapter module plugged in 100% into the socket?

However like Dominic pointed out, if the engine is running and the SES is on with no error code set, the ECM may be running in limp home mode. In limp home mode the engine will run like you are describing, rough due to low spark advance and very very rich with fuel.

Like Jeff said, test the ECM in a ZR-1. You can install it in any model year ZR-1. You will get a SES and different error codes depending on the differences from '90 to '95. However, if the ECM is good the ZR-1 will idle smoothly and without excessive fumes.

07-05-2020	#44
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 252	Re: Extreme rich condition It looks like everybody's ideas are heading in the same general direction. If the ECM blinks a code 12 it means that the ECM has passed the power up self test. That suggests a good ECM. Is the chip adapter module plugged in 100% into the socket? However like Dominic pointed out, if the engine is running and the SES is on with no error code set, the ECM may be running in limp home mode. In limp home mode the engine will run like you are describing, rough due to low spark advance and very very rich with fuel. Like Jeff said, test the ECM in a ZR-1. You can install it in any model year ZR-1. You will get a SES and different error codes depending on the differences from '90 to '95. However, if the ECM is good the ZR-1 will idle smoothly and without excessive fumes.