F430: O2 sensor replacement

Hi all. Recently replaced both my pre-cat O2 sensors - the one on the header and before the main cats. Bank 2 was running rich so I decided to replace both banks at the same time. I reset the ECU and then performed the standard ECU relearn procedure. All was good for a week but now bank 2 is fine but bank 1 is running rich. Should I have performed any other process when replacing them or do you think the new sensor for bank 2 was faulty?

 

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

 

Thanks guys. So yes the ECU has been remapped (by DMS) but the car ran fine for about a year after that. I picked up that the bank 2 exhaust was running sooty a month or so ago and determined it was the pre-cat O2 sensor on it's way out. No codes but that's a common maintenance item when one bank is running rich and an easy fix. Replaced that one with new and all sorted - car running perfectly again - in fact MUCH better. Being the dumbass I can be I figured if that side went then the other side is probably on it's way out so I replaced bank 1 O2 as well. One day out on track and I get home to find the bank 2 exhaust is spot on but now bank 1 is running rich. My first instinct is to reverse the last thing I did - i.e. assume I bought a duff sensor and put the original bank 1 O2 sensor (the one that was fine) back in. If that doesn't sort it then I will follow the suggestions made.

 

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.

 

As you say, DMS are a reliable outfit. I had the conversation about this with them when I had it done. They will dial down the O2 sensitivity if you have (or plan to have) non-cat headers installed but I declined. Took the car out again today and CEL is present reporting misfires on all cylinders on bank 1 - although exhaust pulses are even from that bank. So first step is switching the O2 sensor back out and if that doesn't cure it I shall look deeper. Thanks for the input.

 

Problem solved. My mistake completely - I fitted the incorrect O2 sensor. Not sure how I managed to order one correct sensor and one incorrect sensor but have now fitted a correct replacement and all is good. For reference the Pre-cat O2 Lambda Sensor part number for the 360, 430, 575, 599 and 612 is 0258007001. Costs about £80. Thanks for the input gentlemen!

 

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...