Have replaced the ECM unit and car started fine after going through the relearn procedures. On the test drive the check engine light came back on and the engine got sluggish then stalled. Now it will not start again. It acts as though it will start then does not. We no longer have the original key only copies. Is this a problem with the fuel system, the anti theft system, or is it something with the new ECM? What is the easiest way to check these systems out?