I just got another motor put into a 1992 Honda Accord, but now the car won't start. Is there a problem with maybe motor car mismatch, or do I have to do something to the computer?

Your ECM must match the new engine, among other things.

OK. Can you tell me a bit more about that, please.

You want to check the Honda Part No. on the ECM and make sure it is the right one for your engine. Does the CEL come on, when you turn the ignition key to ON? Do you hear the main relay click? Do you hear the fuel pump, in the gas tank, run? Have you repeatedly turned the ignition key on/off, in order to pressurize the fuel rail?

See the thing is, I have a 1992 and the motor is a 1991. The mechanic got everything installed correctly, it's just that the car doesn't start. So is it simply (or maybe not so simply) that I have to get an ECM put in the car that matches the 1991 motor?

1992 to 1995 Hondas are a different series from the 1988-1991. There could be subtle differences in the ECM, ECM wiring harness, etc. that could cause problems.

So was it a mistake to put in the 1991, or can I get another ECM?

I can't really answer that question. Go to the following site and ask that question:

redpepperracing.com (Powered by Invision Power Board)

These guys are more into engine swaps and should know first hand the complications that come with it.