I am having problems with a Ford Ranger not starting. I believe the problem lies within the FMV (Fuel Metering Valve or 'SCV'). As the car is out in the middle of nowhere, I was wondering if I can connect a 3V analogue signal to it and have it operate correctly, as it is only just a solenoid, to see if the car runs. My understanding is the PWM signal just digitally 'flicks' the solenoid on and off @ 351hz - 1.05v to 5.4v, keeping it in a steady position. So would an analogue signal at a steady 3v using a transformer keep it in the same position?
No, that's not how solenoids work. Positional control is not about average power, it's about specific, timed impulses which result in continuous control.
Solenoids only really have open, closed or travelling between. Either your supply enough power to open the valve and it opens, or you don't and it stays closed (or vice versa, depending on whether it's normally closed or normally open).
Solenoids are usually set up so that their time constant allows enough time for the valve to fully open or close in one PWM cycle, thus a 50% PWM will result in the valve opening for 50% of the time and closing for 50%, resulting in an average of the valve being 50% 'open'. It's not quite that simple of course, bit that gives the basic idea.
I'm guessing no or it would use DC from the start. It could overheat with constant DC current.
I would say yes. It's the total power delivered you are looking at, hence 3V of continuous DC voltage should do the same thing as 3V of PWM signal (assuming the current drawn is the same).
On the other hand if it was digital signal processing you were looking at, it wouldn't be the same as PWM is a switching signal, switching between min V and max V, whereas normal DC signal is completely continuous (does not have discrete parts). That would mean if you were trying to read PWM signal and treat it as analogue you wouldn't get the same behaviour or readings.
EDIT: See Mark's answer instead, you have to be COMPLETELY SURE that nothing else connects to the power line apart from the solenoid itself.