I have a 1998 S70 that stalls after driving at highway speeds for more than an hour. I will go down the highway for about an hour or two, stop for gas, food, ect, shutting off the car to do so. I get back in, start it up, drive away no problem. After a few miles it starts to hesitate, then clears up for a little while, then stalls at low speeds.

I checked the computer for codes, there were none.

The car has 173k on it. looking under the hood there is no obvious problems.
I am a mechanic, just not familiar with Volvos and my girl decided to buy one, need some help figuring out what direction to go with this, since there are no codes to guide me.

 

That's about the mileage the fuel pump starts to die. Since you're a mechanic, next time you take it for a ride, take a fuel pressure gauge with you; there's a port on the fuel rail. Could also be fuel pump relay too, but am betting it's fuel related since no codes.

Since you're a tech you should be able to diagnose which it is I would think, but shout back if you want some tips.

These are very nice cars, but this is a quite common issue at this mileage.

 

I had a feeling about the fuel pump. I think I will throw a new relay in just to see but it does feel like the fuel pump

 

50psi fuel pressure is what I should look for?

 

About 43-44 psi; should go up a few psi when you blip the throttle.