No codes? That's surprising, given all the trouble and current state of non-operation.

Being a "tested/used" part when installed 2 years ago puts the pump on the suspect list. But I'm not sure if your '91 740 has a port for a pressure test gauge to be attached at the injector fuel rail like my 940 does. I'll try to post a photo if I can.

OK - Here's a shot of my 940 showing 2 options for fuel pressure gauge attachment. If your car has the one with the "?", you might find a gauge for $50 or less. But the fitting to connect it (like on a bicycle pump hose) could be scarce.

The other gauge shown is more like $100, but it can be inserted at the connection where the rubber fuel feed line connects to the hard line going to the injector rail, and left in place for testing on the road.



I'd be a bit uneasy with all those "aftermarket" parts, but at least your O2 sensor is the correct type. I feel more confident with OE Volvo parts. More expensive yes, but available online for about 30% off list price from Tasca Volvo.

Be back tomorrow probably...
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.