I just bought a 1989 vert, and noticed that the check engine light was on. I am getting codes 18 and 20. Is my MOP failing? Could the engine or ECU be damaged as a result? What should my next step be?

 

To start, suspect poor electrical connections. Check and clean the relevant electrical connections. Check, clean and if necessary replace your battery terminals. There is a bank of solenoid valves at front left of engine. Remove the electrical connectors one at a time and using sandpaper clean the male spade connectors.

 

Go to Foxed.ca and view the fuel and emissions section of the 89 FSM. Page 26 shows how to troubleshoot code 18, Code 20 troubleshooting is outlined in the lubrication section page 16. Hope that helps.