Cel p1123 p1125
 

99 Boxster Base So after much work and money. New Batt, AOS,MAF,Plugs,Fuel Filter,Air Filter,Gas Cap,Oil Cap o-ring,Cleaned TB, Timing,New VarioCam Solenoid, Repaired DME, I'm getting a CEL with P1123 P1125 codes every 600 miles or so****for rich fuel on both banks. Checked as best I could for vacuum leaks, Fuel regulator I think is within spec for vacuum Maybe on the low side. Any thought as to what I do next. Car is running good says I'm getting 26 MPG on the H'way which is hard to believe. Out of ideas!!! V

How did you check for vacuum leaks? With the work that you did it might be best to get it to a shop that can do a smoke test.

If I am interpreting the Porsche codes correctly (I get them backwards sometimes).
The engine is running to rich and the DME has reached it's limit on how much fuel it can cut. Since it affects both banks it is unlikely that all six injectors are leaking.
Or that both o2 sensors are bad. (although stranger things have happened)
So I would start with a fuel pressure test. (system could be over pressurizing).
Mine is a 2000 S and it has a place (presta valve?) to hook up a pressure gauge on the fuel rail. I believe there is a spec. for key on engine off, and also a spec. for engine running at idle.
I believe your 99 is the same.

Also I believe there is an external fuel pressure regulator on your 99 that can be tested but I am unfamiliar with the testing procedure and specs. on it.
Those two test would be my starting place.
Hope this helps

Sorry just re read your post and see that you have tested the fuel pressure regulator.

You've already thrown the kitchen sink at it, so I can't imagine what else to try except the air/fuel ratio sensor.

Vacuum and air leaks can be difficult to check/find. +1 on having a shop do a smoke test on it. Preferably an indy with Porsche and Boxster experience. My guess is they will only charge you an hour labor +/- $100.

Wouldn't a vacuum leak make it run LEANER? The OP's problem is that it's supposedly running rich.

It will run richer. If it runs really rich you could even smell it. Have an 01 S I am working on right now that has a leak and is running rich enough you can smell it in the air.

Help me understand how. My understanding is that the MAF meters the air coming in and the ECU adjusts fuel accordingly. If you have a vacuum leak, there is unmetered air coming in, causing a higher air to fuel mixture, thus lean. The air/fuel (O2) sensor would sense a lean mixture and tell the ECU. The ECU would enrich the fuel trim to compensate. If the Fuel Trim reaches its limits and still can't get it rich enough, the ECU throw a P0171. System too lean.

What am I getting wrong here? How would a vacuum leak cause a rich mixture?

Thanks.