F430: O2 sensor replacement

Have you considered or checked for any other reasons why it may be running rich?

If it had been running rich before possibly it may not have been the o2 sensors in the first place (although I recommend replacing the pre-cat ones anyway as they are used to adapt the air to fuel ratio's by the ecu by sniffing the results of combustion).

Are your ecu's remapped?

 

I was thinking the same thing... maybe a fuel injector is putting out too much fuel. Or would that cause it's own fault code?

 

MAF may not be reading correctly and there would be no CEL

 

I asked about ECU tuning as I've seen some tuners run afr (air to fuel ratios) quite a bit richer than the factory base maps.

... Also a trend I see is to disable a lot of engine protection and error classes. This is something I'm not that happy with. I hope your tuner didn't just turn things off to make it easier for them, rather than calibrating things properly and leaving protection enabled. Otherwise when errors do occur you may need to investigate without necessarily having the ECU inform you of possible faults. I've even seen some tuners turn off detonation detection! Having said that I believe DMS has got a good reputation so I don't suspect they would be doing this but without looking into it myself I'd always have that nagging doubt.

 

Just for completeness I will describe exactly what DMS seem to have offered and I why I don't feel worried about it myself...

In fact I would go to say it's no trouble to delete 2 of the 4 O2 sensors completely if you don't have US smog to pass like in EU where the test of emissions is conducted by a gas sniffer and doesn't rely on cars ecu to tell it it's ok! Which is stupid when you think about it... VW engineers look away now

Pre cat o2s
Anyway, there are left and right banks which are Basically from the point of this discussion entirely separate. Either bank has a pre (before) catalytic converter, O2 sensor and also a post (after) sensor. All O2 sensors do is sniff the pipe and report a voltage back to the ECU. On post 1997+ model year cars Pre cat ones are typical wideband (meaning they measure entire range).

On the 360+/F430 they do indeed use wideband Bosch O2 sensors pre cat to adjust the mixture of fuel to air to achieve lambda, which is the 14.7 parts air to 1 part fuel for ideal combustion of fuel to air. They are very important to ensuring your engine computers can adapt (trim) the fuel mixture by + or - 20% to take into account faults like leaks in gaskets or even old fuel injectors which slow down with age. All good so far...

Post cat O2
The secondary O2 sensors are actually only really primarily used to sniff O2 to determine how efficient the catalytic converters where at conversion. If they are not working within the programmed thresholds they will illuminate a CEL light. Cat efficiency code.

Only if your primary O2 sensors have become defective the secondary ones get used as a fallback and anyway you're already at the door of a CEL by then anyway so it makes little difference. If all 4 where defective it falls back to the equivalent of safe mode to protect engine so performance is degraded.

So really if you entirely delete the secondary o2s there is very little negative consequences of them other than not knowing that your cats are working as efficiently as you'd expect as it won't illuminate a CEL, which you can get tested anyway at an MOT testing centre with a gas analyzer machine.

The benefits for the enthusiast are that high flow cats which may trigger efficiency codes (yet still pass emissions tests!) become one less worry. So you can either leave secondary o2s in place and just fiddle with calibration values or remove them entirely which will trigger monitoring issue for SMOG testing built into the ECU unless you ofcourse patch that code to fake readiness too but it's obvious with a quick glance in the engine bay they are removed so ...

Hope this is useful to someone...