Oxygen sensor replacement - anyone went thru this?

[Anzezaf]

I had some trouble today at the annual road-worthiness inspection (MOT) regarding my exhaust gasses. I decided it's time to sort this out for good, and not be on edge every year, being afraid if I'm gonna pass emmisions or not.
First step, I'm gonna source a good catalytic converter just to be sure.
The part I'm not sure about is the oxygen/lambda sensor, I don't know how to check my existing one, and I don't know if aftermarket sensors are any good. The OEM one is 200 quid, so that's a bit of a " "
So yeah, if anyone had trouble with the oxygen sensor, please drop a reply - how did you find a replacement, what were the symptoms etc.?

[Max]

I had a similar struggle and couldn't find much wrong other than a loose fuel pressure regulator (my fault) and i replaced the O2 with a new one, part number 36531-P5P-004, this was in 2018 and although i found the email from ebay the listing cant be found and ah-car parts don't list one anymore, i want to say it was either Bosch or Denso as that's the only brands i would trust on a Honda.

Anyway the upshot is the sensor made no difference, the values were slightly different but that could just be down to atmospheric conditions at the time, in the end i went and had a new cat welded in which made a massive difference and the car flew through the MOT.

I've always had a niggling feeling that the car wasn't putting out the power it should do and after a bit of googling i learned about the intake resonator, when i had a look at it i discovered that not only was the vacuum line disconnected from the controller but the actuator was rusted shut so the whole time i owned the car it was breathing through a straw. Obviously not good, so i removed the whole resonator assembly and plugged the vacuum line, reset the ECU and took it out for a drive and it seemed noticeably improved.

After this I've adjusted all valve clearances and once again the car was noticeably improved and smoother, it was quite surprising really how much of a difference it made.

I don't know what effect the above changes have had on the emissions since the new cat as the cars been off the road and not had another MOT since, but im looking forward to finding out as i still have the readings from the last one.

I did post my progress and emissions readings so have a look and see if it correlates with yours.

viewtopic.php?f=5&t=22286

Before you go spending the money on the O2 it may be worth checking those valve clearances as other suggested in the thread, and checking the intake resonator if you haven't already.

Hope that helps.

[ek9sid]

Not quite prelude but I had to replace both o2 sensors on my civic (1.6 sohc). To start off with, I got cheap ones from ebay. While they got it through its mot they would often throw an EML with the codes reading o2 sensor reading out of range (running rich). It was the pre- cat one first which I replaced with one from a breaker which solved the issue for a while but now the post cat one is playing up. OE ones are Bosch on the civic.

If you go for a replacement, I would be wary of the cheapo ones. If possible, I'd go for a Bosch one (or whatever the prelude OE one is - it should be imprinted somewhere).

Be wary on replacement though - they can be very corroded in there. I've rounded a few off in my time using an open ended spanner on them. Definitely worth trying one of those specialist sockets that you can get. I believe they're 22mm.

I'll have a look up to see how to test them. I'm sure there's a way

[ek9sid]

Page 11-72 onwards in the service manual is about the o2 sensors (5g). Maybe worth a look?

[Anzezaf]

Thanks to both of you.

Max, I doubt the intake resonator would have an impact on emissions since it only opens up at a higher RPM? I heard someone somewhere sometime say 4300 rpm But other than that, it seems that a new cat solved all your woes?
As I'm hoping it will in my case, since valve clearances were done on mine, and fuel economy isn't that bad so I presume the fuel pressure is within spec.

Ek9sid, the OEM ones on the prelude are supposedly NTK (the same fellas that make NGK spark plugs) and it costs 30-40 quid so yeah, I totally agree with your point - original or OEM equivalent is the way to go. Everything else is a waste of time.

[Drax]

ive replaced mine on the 4g in the past with either a Bosch or Denso, been all good so far

[Max]

Max, I doubt the intake resonator would have an impact on emissions since it only opens up at a higher RPM? I heard someone somewhere sometime say 4300 rpm But other than that, it seems that a new cat solved all your woes?
As I'm hoping it will in my case, since valve clearances were done on mine, and fuel economy isn't that bad so I presume the fuel pressure is within spec.

I'm under the impression it opens at 2500 ish, and its the 4 butterfly valves inside the intake manifold that open around 4500 ish

Yes new cat solved the issue

[RattyMcClelland]

O2 sensors are around £50..nothing expensive.

Intake manifolds valve KY jelly machines.....I deleted everything and it still passes without any of the valve gubbins.

[Anzezaf]

The thing that is irritating me beyond belief is the fact that I bought two new catalytic converters and none of them catalyzed to any meaningful extent (one was from cats2u.co.uk, brand name BM catalysts, for about 80 quid)
Granted, they were both the cheaper options, but still.. A user or two from on here told me they had success with a converter like that. Plus a mechanic told me it should pass emissions but it didn't..

Guess it's time to find a proper one

[Drax]

Granted, they were both the cheaper options, but still.. A user or two from on here told me they had success with a converter like that. Plus a mechanic told me it should pass emissions but it didn't..

how old are your spark plugs? ive had to change mine in previous years to pass an emissions test