start the car, unplug that vacuum line from the back of the FPR, see if fuel is dripping (or gushing) out of the FPR... the engine might surge when you do this, as removing the vacuum will increase the effective fuel pressure, which means it will idle rather rich until you plug the hose back in.

probably be smart to have someone at the ignition key ready to shut things off if you have a gusher. standard disclaimer: avoid sparks, do this with plenty of ventilation, have a "B" rated fire extinguisher handy, etc etc.

if nothing comes out, then chances are pretty good your FPR is OK. The definitive test is to hook up a fuel pressure gauge, but this requires one with a Volvo compatible threaded T adapter, and not just a shraeder valve like many domestic cars use. The fuel pressure gauge connects between the incoming fuel line and the rear end of the fuel rail... many also have a T fitting for the vacuum line so they can measure the vacuum differential (the pressure should be 44 PSI +/- 2 above the intake manifold vacuum...)

 

My son's 740 used to be a "gas pig" and used to stall at random times, was totally gutless, on occasion it would hesitate. It took me a while to go through all of the problems and fixed them, here is what I fixed:


1/ Intake manifold gasket leak - over time this got worse and we were able to hear it. [ the previous owner/mechanic did not clean the head/intake manifold properly when replacing the gasket... ]
2/ Timing belt was one notch off [ again credit to previous owner/mechanic ], as someone mentioned on previous post, this timing is critical for proper operation.
3/ I just replaced plugs, ignition wires, distributor and the rotor. Even though the distributor looked new, the rotor was VERY old, it fell apart in my hand trying to pull it off. I use the Bosch +4 plugs, measurable minimum 0.5 m/gallon gain plus more pep. I went back and forth on plugs to validate, I have these on my son's and my Volvo 740. The last problem that the car had was shorting to ground on the distributor rotor.

Now the car has at least 2x the power, no hesitation, starts practically immediately [3 to 4 barks], even when it is -20F. I am not sure about his mileage, however he does say that he drives lot further on a tank.

My mileage on a 740 Turbo is 22 mpg in Summer and 18 mpg in winter, both would be combined city/highway. I expect his to be similar now.

One point on the gauges, they are VERY inaccurate.


Hope this helps.

 

"2x the power"? Timing belt being on correctly will do that... The rest, not so much.