The problem is that our RS4 B5 is running so rich as rear bumper gets black after few pulls and it smells very gasoline like@idle
It also has very unfriendly L/100km figures, almost 25L+ per 100km when cruising at 100km/h.
Checked our MAF / O2 readings with VAG.COM , then compared to friends RS4 B5 readings and this is what we came up with:
MAF readings @idle@90C – both cars have the same readings ~4.5 g/s , so it seems MAF sensor is in working condition.
IAT readings @idle@90C – both cars have the same readings ~40C , so it seems IAT sensor is in working condition.
Here comes the nightmare:
Pre cat o2 readings @idle@90C (our car) = 0.815 - 0.87V , never goes lower than 0.8V (too damn rich);
Pre cat o2 readings @idle@90C (friend’s car) = fluctuates between 0.1V-0.6V (normal situation for narrow band o2 sensor showing stoich air-fuel I suppose)
Group 033 O2 sensor Diag status readings @idle@90C (our car) = 0% , never ever changes.
Group 033 O2 sensor Diag status readings @idle@90C (friend’s car) = fluctuates between -2.3% and 0.8%
Group 078 Air mass (g/s) sec.air.inj. @idle@90C (our car) = -100% , never ever changes.
Group 078 Air mass (g/s) sec.air.inj. @idle@90C (friend’s car) = -3.1% , never ever changes.
Thermostat and CLT sensor were replaced with OEM new ones few weeks ago.
Engine does not throw any “fuel trim too rich” or “o2 sensor problem” codes, everything is clean even after driving 200km+ trip….
All the coil plugs are black and dirty after inspection.
Haven’t checked the fuel pressure in the rail (as it’s too time consuming to install T-fitting with gauge), but have never heard of FPR’s to go bad. I could replace it with other 4BAR FPR for testing purposes.
Any suggestions?
P.S. Please don’t blame tune as our car was running great (10l/100km cruiser) with exactly the same tune before.
