When I started my 2003 v6 it was really misfiring. Then smoothed out. I drove onto the main road and it missed again. At the stop light it konked out. After several trys, the police pushed me to the side of the road. I tried it several times, it just turned over, but would not start. While waiting for help, after 10 min I tried it and walla, it started and runs fine again. My mechanic says as no engine check light came on there’s no way to tell what happened. As an old old timer, I don’t want to get stuck somewhere. Thanks.
I would have someone actually hook up a code reader and see if they find anything. Many auto part stores will do that for free. If they find a number post it as a reply to your original message. It should be in the format [P1234].
Assuming nothing from above, I would look at the fuel filter (when was the last time your changed it? or a fuel pump problem.
It would help a lot of you could check for a spark when it is not starting. The easy way is to get one new spark plug and when it is acting up, just remove the spark plug wire and put the new plug on it. Hold the threads of the new plug tight against the engine block and have someone try to start the car. You should see a bright blue spark. If you see stars, then you likely failed to hold the plug with a well insulated tool.
What does an engine need to run? It needs: 1. Spark, 2. Fuel, 3. air. Your mechanic needs to make sure that those are working at the right time, and at the right values. For example: fuel pressure; spark strength and regularity; correctly controlled intake air (air filter, idle air control valve).
Half the battle of troubleshooting a system is understanding how it normally operates (be it a human body or a machine).