Lambda / Oxygen Sensor

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Armstrong
Joined: Tue 07 Feb, 2017 22:02
Posts: 2

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Lambda / Oxygen Sensor

Post by Armstrong » Tue 12 May, 2020 01:16

Hi,
I need you guys to advise please. My wife's got a 1997 (R Reg) 1.9 M44 engined Z3. Last year it scrapped through its MOT with it real close to failing its 2nd fast idle test, in fact it failed the test first time, so I fitted new Spark Plugs and stuck Wurth fuel treatment in the fuel tank and gave it a good 20 mile thrash up the motorway to ensure the cat was up to temp and it just scraped through. The exhaust is a replacement about three years ago including the cat. However, the exhaust only has one Lambda / Oxygen Sensor!!!! which is post cat and it should have two according to the Bentley workshop manual.

The pre cat Lambda / Oxygen sensor is missing and the exhaust has a blanking plug screwed into where it should fit. Ive searched for the pre cat electrical plug socket from the main wiring loom from the DME M5.2 ECU, but I can't find it, both from below the car and from the engine bay. Anybody on here able to shed some light on its whereabouts please, maybe with a picture to help. I'm probably looking in the wrong place and I can't find any references on the Net.

The car goes like a bomb and is great fun to drive.

Many thanks

Jon

Jonco
Joined: Sat 04 Jun, 2011 08:24
Posts: 390

  Z3 roadster 1.9
Location: Cheshire

Re: Lambda / Oxygen Sensor

Post by Jonco » Tue 12 May, 2020 21:10

Mine is the same - European models only have a single sensor. Double sensor was American market. Realoem confuses this set-up.

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Robert T
Site Admin
Joined: Mon 12 Jun, 2006 11:35
Posts: 10097

  Z3 roadster 1.9
Location: Cheshire

Re: Lambda / Oxygen Sensor

Post by Robert T » Tue 12 May, 2020 21:52

Having everything up to temperature seems to be key to the emissions test. My local indie leaves the engine running whilst he checks everything else first.

I take it the replacement exhaust is not BMW? Aftermarket cats seem to vary in quality. I'm on a BMCatalysts one and the car passed no problem again this year. It wasn't expensive, so I don't expect it to last too many years, but I'm hoping for 5 or so.

One thing to check, particularly on the M44 is the rubber intake boot. These split and let air in unmetered air, which upsets the fuel air mix and confuses the ECU with the lambda readings.

Cheers R.

Sent from my SM-G960F using Tapatalk

Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
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Del
Joined: Sat 19 Nov, 2011 18:35
Posts: 2136

  Z3 roadster 1.9

Re: Lambda / Oxygen Sensor

Post by Del » Tue 19 May, 2020 10:49

Agree with the comments above. Only one pre-cat lambda on the UK M44 engine. If it's struggling on CO at the MOT it's often the aftermarket Cat

Armstrong
Joined: Tue 07 Feb, 2017 22:02
Posts: 2

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Re: Lambda / Oxygen Sensor

Post by Armstrong » Wed 27 May, 2020 23:56

Hi Del, Robert and Jonco, apologies for the late reply but my work got in the way to responding earlier. Many thanks for your very helpfull reply's, yes it was a cheap aftermarket exhaust and CAT and its quite loud compared to the original BMW one I replaced it with. Thanks for the tip Robert, I looked up BM Catalysts, just out of interest how much was yours?

Anyway, just for information and I hope this helps someone else out so here's what happened to our car.

The original CAT disintegrated in the exhaust and blocked the exhaust flow. It took me several days to work it out after my wife complained of lack of power. It was just awful and felt like it was driving on two cylinders after it warmed up and just wouldn't accelerate, just juddered and felt strangled. I checked everything including the rubber intake boot for splits, changed the plug leads and plugs and coil pack, checked the fuel pressure and cleaned and serviced the fuel injectors, dry and wet compression test, all OK. The only option it could be was the exhaust, when I took it off, the CAT rattled and chunks of honeycomb fell out. Bought and fitted a new (cheap) exhaust system and the bugger took off like a bat out of hell, problem solved. I hope this helps someone else who may have a similar problem.

Jon

Jonco
Joined: Sat 04 Jun, 2011 08:24
Posts: 390

  Z3 roadster 1.9
Location: Cheshire

Re: Lambda / Oxygen Sensor

Post by Jonco » Thu 28 May, 2020 11:44

Glad you have it sorted. When my original cat was fitted, I heard the warning rattle and changed it before it disintegrated. I have a Cobra cat back system mixed with reasonable standard front pipe and cat fitted now. Cat had 3 year guarantee but it is coming to the end of its' life after 4 years so will need to change for next time.

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