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Here's a nasty problem that took four months and some dogged detective work to solve. I bought a 1988 245 wagon on ebay and went to Philadelphia to pick it up. The car had low mileage and looked great. But it was running when I arrived to collect it, and the temp guage read very hot, but not overheating. Since I had a 120 mile drive home, I didn't turn off the engine until I reached my driveway. It restarted fine. The previous owner had drained some coolant to raise the engine temp. Why, I didn't know.
Next day I drove for half an hour and turned off the engine in Wal-Mart. That's what I get for going to Wal-Mart. After 10 minutes it wouldn't start. After the engine cooled for half an hour it started fine. I drove it to my independent Volvo mechanic, Hans. He tried it, and it started. I drove it home, turned it off, and couldn't start it for an hour. My wife, of course, delighted in reminding me of the folly of buying old Volvos and bringing home stray cars I find on ebay. Don't blame Wal-Mart; it also happened at Home Depot also.
The problem continued. It was totally random and intermittent. One by one, I eliminated the ignition system (lots of spark), the fuel pumps, the fuses, the idling motor. Then I checked the oxygen sensor with a voltmeter and discovered it wasn't operating properly. Replaced it. Problem persisted. Used additives in the fuel and changed both filters. Problem persisted. I was preparing to replace the air mass sensor, when I brought it to Hans again. Needless to say, the car ALWAYS started when Hans had it, and REFUSED to start once I ventured more than five miled from his shop. Hans poked around the engine block and discovered the engine temperature sensor was broken. This is hidden up by the manifold on the driver's side. Consequently, the emissions system was being fooled into thinking some starts were cold starts, and flooded the engine. The minute the sensor kicked in again, the car started.
Hans said he had never seen the problem before.
What did we learn from this? If a 240 4 cyl engine with emissions balks at starting while hot, suspect the engine temperature sensor before expensive replacement of the emissions system or fuel pumps. Note: this sensor is NOT the temperature guage sensor, which is easy to access. An inexpensive replacement and some logical diagnostics solves a very nasty problem.
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