I'm helping a friend with a 2001 Montero Sport (V6 3.5L). Went to pick it up tonight and encountered this problem. It started right up, ran for 5 seconds (sounded normal), and then immediately died (as if the key had been turned off). Not sputtering, missing, roughness, or anything. I immediately tried to restart it -- same story. Started right up and then died even more quickly. Repeated the same thing a third time. By the fourth attempt, it would crank but not start. I waited 2-3 minutes and then it started again - but also died just as quickly. Fuel tank registers half full. Any thoughts?

 

I decided to follow my instincts and opted to start with my first suspicion - the fuel filter. Purchased a new fuel filter at the local auto parts store ($25) and replaced it this evening. [The fuel filter is located on the driver's side of the vehicle, attached to the frame, just in front of the rear tire. It is held in place by a bracket attached to the frame with two bolts.] Following replacement, the engine started right up and seems to be running fine. I've driven the vehicle several miles this evening and all seems to be normal. Unless the problem reappears in the near future, I'm considering this issue resolved.

 

After a week of test driving my friends Montero -- and thinking my fuel filter replacement had done the trick -- I went out to start it this morning and "presto chango" it starts and then immediately dies. Tried a couple more times, same thing. I'm thinking I'm right back to "Square 1". Then, for whatever reason, it dawned on me that she had given me two separate key rings for this vehicle; and I was using a different key today versus what I had been using all week. I got the other key, started the car and the engine runs perfectly. I switch keys, start the car, it immediately dies. So, I dig out the owner's manual and discover that Mitsubishi has incorporated an "electronic immobilizer" module in the ignition as a theft deterrent. It operates using a transponder-equipped key that has to be programmed to match the module on the car. Apparently, one of the keys has been de-programmed or otherwise rendered a non-match. The interesting part of this story is that the manual says that if a non-programmed key is used, the car will not start. In my case, it seems the response time of the module is slow enough that the car is able to start but then the module kills the ignition and shuts it off within seconds of starting. I am now convinced I have found my problem. I hope this may help others who encounter a similar situation.