Mercury mystery.
 

In June 2008 I bought a 2000 Marquis with fewer than 96 k.m. on it.
Before long it developed an intermittent starting problem. Sometimes it would not start, although the engine turned over perfectly. During last winter I took the car off the road in frustration and used my other car. I returned the Marquis to the road about two months ago and am about to lay it up again.
I have had the car examined by seven "mechanics" - two from Mercury dealerships and have got absolutely no satisfaction.
The diagnoses are "fuel pump", "definitely not fuel pump", "defective key", "defective security alarm", "defective rear-end alarm","don't know",..... While lots of money has passed from my possession.
So I now have a visually perfect car which is of absolutely no use to me and which I cannot sell. My best hope is that someone will steal it.

anyone think to check for an intermittent starter solenoid?

my 88 MGM has an intermittant throw-out hang up and sometimes the starter just doesn't engage the flywheel (or falls off the flywheel). I just wait for it to spin down and try again. sounds to me like yours is not even engaging the starter in the first place. I had another car many moons ago that did that. turned out to be a flaky cell in the battery. when the engine was at operating temps, the heat would drop out a cell of the battery and cause the starter system to not engage due to low voltage. once the engine cooled and the battery cooled a bit, it would come back and I could start the car. if the newer MGM has the starter safety circuits like that to prevent the starter from over amping and burning stuff up, then that may be your problem. Through all of this, did anyone think to check the battery when hot?

if it was my car, I would put a fuel pressure guage on it and check the fuel pressure while turning over the engine. It will probably need fuel pressure in the high 20's or low 30's (lb per sq in.) in order to start. if the fuel pressure is ok during the no-start conditions I would figure out a way to check for loss of 'spark' or ignition. If it always has good spark and fuel pressure I would check for voltage at the injectors. Hope this helps.

By the way, When does it not start? When the engine is cold or hot? Does it ever quit running once it starts?

I am guessing electrical. Maybe the ign. ctrl. module. When it turns over and does not start, does it sound any different? Listen for that fuel pump prime for sure, to rule it out. Any more details would be great. Let us know.