Couldn’t work out how to use the diagnostic plug but here’s a link to a video I’ve made using my NA. The O2 sensor plug on your car should be on the front of the engine. I pushed a bent paper clip down the side of the wire. With a warm engine you should get that swing in voltage from the blue wire. Slowly at idle and faster at 2000 rpm.
Interesting, my mk1 was borderline O2 last MOT. I plan to check the output of the sensor with an oscilloscope in two weeks time. If I can find a way to capture the waveform I’ll post it.
Ooooo lovely!
Is there a OBDII connector near the internal fuses on my 1999 NB?
Ive had a look and can’t see it!
Thanks
Regards
Nic
No, they’re only on facelift. The 6th from last digit of your VIN is a 1 isn’t it? Needs to be a 2 to have EOBD.
Yep it is.
Thanks
Nic
My 2p worth.
After the cat was stolen off the wifes NB (I have NEVER seen her so cross!) I fitted a repro cat. That always needs to get almost red hot to pass, the repro cats are simply not as good as originals (hence being a fraction of the price)
Last MoT it went in after being thrashed at 5k for 15 minutes (2nd gear) and tested immediately. Failed. Tester sat revving it hard for a few minutes, and got the readings down just far enough to pass. The engine etc was HOT.
Luckily I have a very sensible MoT station near me. A jobsworth would fail it…
Id agree with the above, if your are going to fit one then at least fit a type approved one.
Most are junk and last a few years at best.
Ok All and thanks for the advice😂.
Which Cat would you advise then, not the OEM at £800 ish I would hope.
Thanks
Nic
Get a BM one, we went through a few before getting one that both fitted and passed all the emissions tests.
I would recommend Cats2U too, very good feedback and quick delivery.
Hope that helps.
Also MX5Bitz are good
Thanks,
Will let you know how I get on.
Cheers
Nic
Hi, just came across this on another thread. If you have a 1
The coolant lines that go to the air valve can become clogged. Meaning the air valve doesn’t shut once the engine is warm causing a high CO.
I finaly got round to checking the O2 sensor output on my MK1.
The first image is at tickover and the second at about 2000 rpm.
I think this is ok as it seems the output should change between >0.85 ( rich ) and <0.25 ( lean ) The only slight maybe is that mine is reading 0.1 at the lowest point and one website sugested this may be a bit too lean.
Any thoughts anyone?
Dave.
PS the horizontal scale is 1 second per div and vertical 200mV per div.
I’d say that looks spot on. I’ll scope mine later for comparison. I wouldn’t focus too much on the actual numbers, it’s the actual switching that’s important.
For not much more reason than a bit of scope CPD and geeky-ness my traces are below.
Idle
2000 RPM
Wide Open Throttle & back to idle
Hi All,
Thanks for all your input on my MOT failure. Pleased to advise it has now passed following a CAT replacement.
I’d previously changed the Lambda sensor which didn’t make a great deal of difference.
More to follow tomorrow, in the meantime are you using oscilloscopes to measure your output?
Thanks Again
Regards
Nic
Good to hear that it’s sorted.
Yes! Don’t we know how to enjoy ourselves!
Morning All,
Just to complete the story.
The Lambda sensor was changed - the one that came out didn’t look that bad to be fair (my cars done 73K). Picture to follow. The % Oxy reading came down a little fròm 37 to around 31.
I decided not to change the Temp Sensor but focus on the Cat - this was replaced with thr £100 approx Cat Kit from MX5 Parts - which finally did the trick - % Oxy 0.02 bang on.
.
Now its off we go for another year with trepidation about nexts years MOT post lay up - The joys of Motoring in an MX5 eh:joy:
.
Cheers
Nic
