I've been having a problem starting my 1989 240 DL when it's warm. When it's cold it starts no problem, I drive it around for 30 minutes and let it sit for 20 - 30 mins and it becomes difficult to start or if it's a warm day outside. Engine turns over several time then cuts out. I push down on slightly on the acceleration pedal and it helps sometimes. I've checked the resistance value of the coolant temperature sensor at ambient and normal operating temperature (after cars been running for awhile) and they look good. I did not feel I needed to remove the sensor and bench test it. I'm leaning towards the pressure regulator. Transfer pump was inoperative. I replaced both fuel pumps and I can hear both of them running; I've noticed a difference when the car is running. I have not check fuel pressure but I no longer feel it's a fuel delivery problem. Any suggestions will be greatly appreciated

 

I would still check the fuel pressure. Then you will be able to tell if the regulator is bad.

 

remember that there are two coolant temp sensors, one for the gage, one for the ecu. Make sure you check the one for the ecu.