240 volvo wagon. occasionally as I am driving, the car hesitates as if it is about to cut off. Almost like fuel or ignition is shutting off. Replaced fuel filter with hope that was problem but that did not fix it. Having suspicion it is fuel relay as occasionally it fails to engage at startup.

I don't think there is a rollover switch on a '91 wagon.
The ECU supplies ground to the fuel pump relay for only about a second and a half if there is no ignition pulse. This is what shuts off the fuel pump in the event of an accident. The transistor in the ECU that provides this ground signal fails after a couple of decades. Repairing it is not a do-it-yourself operation but there are rebuilt ECUs available from multiple sources. Be sure to get an ECU that is compatible with your vehicle configuration.

the fuel injectors are notorious for getting gunked up,use redexe/wynns full can to 1/2 tank gas,may cure it but worth a try anyway.....

Check the left front fender area under the hood. If it is not there, it will be located under the car, right wheel area.

Hope this helps.

undo the line before the fuel delivery system and let it run til it stops burping

Try to reset your computer ,pull off your pos batt cable,for about 5mins,also replace your fuel pump relay.

you may want to check the fuel pump relay. this is a common problem

sounds like you have a computer glitch. i would take it to any auto shop and pay 50 bucks so they can take a look at your e.c.u. (engine control unit) we had a similar problem a few years ago with our 1990 volvo 740 gle 2.3l station wagon. it was a glitch with the computer. got a mixed signal with the mass air flow sensor.

Check for vacuum leaks,pull off your intake hose and look for small cracks,also go to the rear of car and listen for you intank fuel pump,needs to making an humming sound,no sound or intermediate this can be your problem.