Engine Performance problem
1996 Volvo 960 6 cyl Two Wheel Drive Automatic 182000 miles
I've got a 1996 Volvo 960 w/2.9L engine 182K Miles. This car has one fuel pump(In-tank).
About a month ago it started occasionally having " spells" where it would sputter and/or stall when I hit the throttle but only
occasionally. Between " spells" it ran PERFECTLY at any throttle setting. It had " spells" with increasing regularity. Eventually it
became " cronic" to the point that it wouldn't even idle. I was stranded. When I came back to the car it started fine and I was able
to limp 10 miles home as long as I didn't give it too much throttle.
I put in a new fuel filter and but the problem returned in a day. The car has progressively gotten worse to the point that it will
start and idle but I can't give it much throttle or it will stall and eventually it sputters and stalls anyway. It " appeared" to be
fuel starvation initially.
I've got a OBD-II device(ELM327) and previous to this problem have had a Check Engine fault with the " Air Injection Unit" but that
code had been showing months and it stayed cleared a few days each time I cleared it. Since it started showing long before this
problem I don't think it's related, but I'm open to being corrected.
When monitoring live data I'm seeing misfires in the cyclinders when it's sputtering/stalling and The " Closed Loop fuel system"
reports an " O2 Sensor fault" but no more detail.
The only hard fault I've ever seen was in the Air Injection System I mention above. It's not come back since I cleared it at the
start of my troubleshooting efforts after limping the car home.
I hooked up a fuel pressure guage. Here is what is happening:
The pressure is 42psi constant at idle - Normal.
If I give it throttle the pressure instantly goes up with it but it never makes it to 50 psi.
If I hit the throttle quick the pressure snaps up but it stalls or almost does.
If I give it throttle slowly it'll rev up to near redline and the pressure creeps up with the throttle. In anycase - too much
throttle makes it stall.
It seems like anything that makes the fuel pressure flirt w/50psi causes it to stall. I mean it almost looks like there is a
overpressure safety switch at 50psi. Does this make sense?
The only fuel related repairs it's had in the last 10K miles has been the fuel rail and the filter I put on it.
Thanks for any advice you guys might offer, I appreciate it.