I have recently acquired a '91 Trooper (automatic, fuel injected, not sure which engine, if there are more than one). It will start instantly, and I mean instantly, without fail, every time when it has been sitting overnight or for several hours. Even in subfreezing temps. The problem occurs when I have driven it for ten or twenty minutes and have occasion to turn it off. It then refuses to start! The starter grinds, but the engine won't fire. This has happened almost every time I've driven it in the three weeks I've owned it. If I walk away and let it sit for at least a half hour, it will eventually fire. (often takes as much as an hour). Needless to say, this is a little annoying in wintertime Montana.

Please don't respond with a huge "DUH!" when I say that the O2 sensor light has been on continuously since I acquired the car. Here's why: The previous owner, a good friend, says that it had been on for quite some time and that he didn't have this starting problem. (The car had been out of service, sitting idle for more than a year prior to my acquiring it.) I have had O2 sensors show false positives on other vehicles I've owned and had several friends experience these false O2 positives also. Based on the previous owners experience, i.e., O2 sensor lit up, but no starting problem, I'm thinking there's a reasonable chance that my problem is not the O2 sensor. If someone has had this problem and fixed it with a new O2 sensor, I'll certainly be persuaded, of course, but I'm unemployed and not at all adept under the hood, so I'm hoping to solve this without making any expensive wrong guesses, i.e., paying for work that doesn't solve the problem. Has anyone had this problem? Anyone got any ideas? If some one can make a compelling case why it would indeed be the O2 sensor, I'm here to listen.

Thanks very much for your time.