I have a 96 850 non-turbo auto with some 172,000 miles.

The car started to have trouble some two weeks ago. My wife complained about "loss of power". It took a while to recreate it: when speeding up (from a dead stop), it lost power. But letting go and flooring it would return to normal operation. The problem was very intermittent. When it did happen, the check engine light would flash (I did not even know the light can flash, before).

Then the next day it died on me on the highway. I could barely get off - it would stall and wouldn't restart. So I towed it home. I thought it was a fuel pump. The old pump died on me some 1.5 ago and I installed a Walbro in there. However, I do hear the pump whine for about 3-4 seconds when the key is on. I also checked there is power going to the pump and I can hear it clearly. I do have pressure at the fuel rail. I did not measure how much but there was plenty of fuel squirting. I do have spark. When warm, the engine is cranking but not starting. When cold, it starts right up, idles fine and I can rev the engine up (with no load). I feel hesitation going from idle speed to some 3,000RPM. However, under any load (going from a dead stop) it just buckles sputters and stalls. I can restart it once or twice but then it stalls at idle speed and I can't restart it at all.

I have OBD-2 tool (from Alex Pepper) and here are the codes I've read immediately after the initial failure:
Time 20:31:47.0 Received from 17
P0172 System Too Rich (Bank 1)
P0133 Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1)
P1310 Not defined
P0302 Cylinder 2 Misfire detected
P1310 Not defined
P0302 Cylinder 2 Misfire detected
P0304 Cylinder 4 Misfire detected

The "System Too Rich" is an old code and has been there for years - I simply ignored it. It does trigger Check Engine light but it eventually goes away (and comes back).

Since then I've been messing with it for the past few days. I tried with MAF unplugged, IAC unplugged (no difference). I even disconnected hose from air box and left the throttle open. Still no start when warm - it was trying to catch, sputtering and backfiring but would not run. When it cools down, it starts up again on the first crank.

Here's what I've checked:
- the pump is on - some 3 seconds on acc position; all the time when cranking
- the whine from the pump altered somewhat as the RPMs dropped but it may have been related to varying voltage as the RPMs dropped below normal idle speed.
- there is plenty of fuel. I checked the schrader valve at the rail and it was gushing fuel for a few seconds when the pump was on. There is definitely plenty of fuel in the rail
- I do have spark
- the spark plugs look OK - some black dust but not fouled (and not wet).
- I do have 12V at the injectors when the ignition key is on II
- electric contacts look fine (no rust)
- I did find one vacuum hose broken - a short thin black line that goes from bottom of airbox to the top. My Haynes claims it is "intake air pre-heating system" (when vacuum is applied, I do hear a flap switching). I do plan on getting a replacement hose but I do not think that's the core of my problem.

I got a fuel pressure gauge but the fitting is too large (there is not enough clearance at the schrader valve to put the gauge fitting) - I need to get a different model to fit the valve.

It could still be a fuel pump problem - the fuel is in the rail but I do not know if there is enough flow. Or perhaps the fuel pressure regulator is not working right. However, the no start situation is very perplexing. I do not want to start replacing parts blindly; any suggestion/advice is appreciated on how to test or fix this problem.

Thank you,
Peter