1996 Volvo 850 GLT Closed loop fault

[lesduc]

Hey guys,
I have a CL-Fault that I can't resolve and am looking for suggestions and next steps. I've read other posts but still in the dark on this one...

I'm using a Autel ms310 but see the same issue with a better Actron ($200) scanner as well, and no fault codes.

Details:
VIN YV1LS5540T1XXXXXX

B5254S Emissions = (4) w/o EGR w/air pump, w/OBDII, w/elec. control evap,
Motronic 4.4

-Replaced plugs, wires, rotor/cap
-Flushed coolant and replaced thermostat (but not coolant temp sensor)
-Replaced both oxygen sensors with Bosch exact fit
-Both scanners don't recognize the second o2 sensor
-Swapped different ECU from same model – no change
-Replaced Purge Valve with Bosch 0 280 142 300
-Fuel pressure appears fine
-No visible vacuum leaks - all connectors/hoses seem to be in great shape at ~100k miles
-Cleaned flame trap and replaced o-ring
-MAF seems fine - swapped in a faulty unit for testing and it wouldn't start/run
-Long term fuel trim is around -6%
-6 Incomplete monitors (car is on the exception list)
-I've seen the system go into CL momentarily (and OL, as expected) while driving but otherwise it's always in CL-fault.

In general, car runs great and has no other issues but NOx was high last time (barely passed) and smog is coming up so I really want to get to the bottom of this. Any thoughts, suggestions?

thanks.

[difflock54]

This link might be of interest / help to you?
http://www.enginebasics.com/EFI%20Tunin ... %20o2.html

It makes mention that a faulty or incompatible cat can cause problems.

Also http://www.mr2.com/TEXT/O2_Sensor.html

[lesduc]

Thanks for the post difflock54.

I've read through a good deal on the closed loop issue and after swapping the ECU i'm seeing CL under different driving conditions, and I'm seeing all INC monitors are now OK. Not sure if ECU was part of the problem at this point.

Looking at the tuning link chart, it seems closed loop occurs under some specific load and some specific rpm for the 3000GT - does anyone have a similar chart/range for the 850? Should I be seeing closed loop at idle once at operating temperature?

What is actually happening when in CL-Fault? It's not OL, and it's not CL...so is there any compensation happening?

I ordered a new coolant temp sensor for good measure - curious if that will make any difference.

[abscate]

High nox is a flag fit an air leak of some kind.

From Eriks post

The control module receives information from the HO2S about the fuel/air mixture in the idling and partial load ranges. If the fuel/air mixture deviates from λ=1 the short term fuel trim will compensate this by adjusting the injection timing so that λ=1 is achieved. When the short term fuel trim carries out this adjustment, its mid-point must be adapted by the long term trim. When the long term fuel trim has adapted the short term trim to a maximum value, DTC 2-3-2 (idling range - 0.48 ms to +0.40 ms) or DTC 2-3-1 (partial load range 0.773 to 1.227) and status message Upper Limit (lean fuel/air mixture) or Lower Limit (rich fuel/air mixture) will be set.

If I'm getting this right, a low limit on the LTFT means you are running rich...too much fuel

fuel pressure regulator ok?
Leaking injector
ETC wonky ( common if you tried non OEM)