Engine Performance problem
1993 BMW 325is 6 cyl Two Wheel Drive Manual 122000 miles
This car passes emissions testing regularly but CO levels have been elevated to 2/3 of the limit for many km (approx. 60k miles). I bought the car recently, got a full inspection II service & fuel system (Terraclean) cleaning. It had drivability issues that improved with the MAF unplugged, so I cleaned it with MAF cleaner & that was resolved. The car also had 3 types of coils (4 Bosch, one Bremi and one Zundspule) so I replaced the two mismatched with Bosch.
Initial emissions scores at this stage were (HC-CO-NOx) 0.22, 6.03 & 0.29. PCV system was checked ok, I swapped in a used MAF and replaced the intake air temp sensor (much better low end & smoother power after) & retested. This produced scores of 0.42, 3.41 and 0.31. HC limit is 0.50, so I reinstalled the original MAF and retested (same day), and it scored 0.21, 6.31 and 0.20. With the new intake air temp sensor, this is its lowest NOx reading on record.
It seems odd that the different MAF would improve the CO but cause HC problems. Scores dating back to ~70k miles are consistently in the 0.3x / 6. Xx / 0.4x range. I have checked emissions scores on friends with the same engine, and their CO scores are much lower, usually < 3.
The car runs very well with the only annoying symptom being a bouncing idle after the car is restarted when warm, but the elevated CO levels concern me. The idle is very smooth once the bouncing stabilizes. Power builds smoothly to redline, the motor has virtually no oil consumption, and compression tests were near perfect.
have the same problem?
Tuesday, April 28th, 2009 AT 1:17 AM