My '92 240 has had an intermittent no-start condition for the last year and a half. The problem began 18 months ago. The car would usually start and run fine, but occasionally it would crank but fail to start, typically after I had driven it around town. After waiting for 45 minutes or so (sometimes longer), it would usually start right up again. The car never stalled or sputtered when running, it just would not restart.

I replaced the power stage and crank position sensor (Bosch on the former, what FCP sells for the latter) but it didn't help. Then I replaced the main fuel pump with a used pump I had. Problem solved! No more troubles for over a year.

Then, a couple months ago, the same no-start condition resumed. Crank, but no start, then the car would typically start right up after a wait of a couple hours. Oddly, unplugging the fuel pump relay and plugging it back in a couple times (to freshen the contacts) would sometimes result in an immediate cure of the no-start.

At this point I figured the used main pump had gone out, so last week I replaced the main pump and filter with new Bosch units.

A couple days later, same story--crank but no start. The car was in a parking lot near my home, so I returned twice the next day, hours apart, and it wouldn't start. I Fosterized two relays, and tried them (along with all the other relays in my bag 'o relays) and it didn't help.

When I went back the next day after that, it fired right up. Then, today, after sitting for most of the day, it failed again. I sprayed some starting fluid into the throttle body, and it seemed to catch a bit, which it hadn't before, without starting fluid.

I'm confused. Replacing the fuel pump seemed to fix it the first time, but now, with the same symptoms, a new fuel pump didn't fix it. The most likely electronic culprits are almost new. And why does unplugging and re-plugging the relay make a difference?

Any help appreciated!