'91 245 194,00miles.
Runs fine if the temperature is above 15 deg F. Below 15 the car will turn over, fire once or twice, but will not start. If I continue to crank the engine and pump the gas pedal, it will fire once or twice then stop.

What I have tried: replaced the fuel pump rely, I always keep a spare. Pulled a spark plug and checked for spark during cranking, good spark. While pulling the plug noticed that it was slightly wet with gas, so there is fuel.

I tried to search for similar fault conditions from others and did find some things but I'm looking for help with the next logical step. Should I aim the hair dryer at the ECU had see if that helps?

Thanks in advance...

Hmmm. 91? That's right around the time the cold start injector was eliminated on the 740's... Maybe on the 240's too?
If not, I'd think the cold start injector is causing issues.

Here's what I'd try. Go out and sit in the car. Turn on the headlights for a minute or so, shut them off. Turn the key to KP2 and wait ten seconds. You should hear the fuel pumps. Without touching the gas, crank the car over for about 3-5 seconds(about 15 chick-a's max). If it doesn't start, let off the starter.
Wait a few seconds and repeat it. If it doesn't start after the 3rd try, then start poking around at some other things.

Good Luck
--
1990 740 Turbo, on its way to stock specs, maybe beyond

How's the battery? At 15 degrees (F, I assume) its power is considerably reduced. Your symptoms sound like there is fuel and spark, just not enough to fire all cylinders.

How many miles on the plugs? Are they the ones recommended? A new set might do the trick.

Another idea - A lot of cranking over without starting can create flooding - too much fuel. Each time the key is turned to "Start" the fuel pumps run a short time, like 5 seconds. Three or four times of this, and the fuel amount sort of drowns the spark. I found that leaving the key off and holding the gas pedal to the floor for several minutes allows some air in and, with luck, the excess fuel evaporates.

Check the condition of the fuel pressure regulator, too.

My newest 240 is a 1988, so things may be different between mine and thine.

Good Luck,

Bob

:>)