So I have a frankencivic.. originally was a '90 standard hb. Many many years go I had a mechanic mount a 5 spd transmission (unknown from where) because he said I'd probably get better gas mileage (which I did). A few years later I had the great idea to try and throw a HF engine ('88 or '89 D15B6) because I wanted it to be a real gas saver.. So it ran okay, some issues mainly my mpg is crap most of the time.. but it runs.. it's still using DPFI with a PM9-L11 ECU. So recently I acquired a PM8-L030 ECU because by chance I ran into someone giving it away.. I switched in the ECU to see what happened The engine sounds like it may be running well. (maybe even better). I even drove it up and down the driveway back and forth 50ft. I haven't taken it around the block (yet). I'm really curious to see what sort of mpg I get on this setup. The only thing is I get a check engine light. Code 4 and Code 16. Code 16 indicates a problem with the fuel injection, which I guess is understandable. Code 4 which indicates a problem with the CKP sensor for MPFI and Vacuum Switch for DPFI. So I have a number of questions: 1) Is it safe to drive my car like this? What is the likelihood of doing some serious damage to the vehicle? 2) Is there any way to fix these errors to satisfy the check engine light. 3) What is a vacuum switch? Thanks!