Micra running rich

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Mon 4 Jul 2005 20:53
Micra running rich - Quinny100
A colleague of mine has asked me to take a look at her 97 Micra 1.0 as someone had told her it was burning oil due to a layer of black dust over the tailgate. Car is approaching 90k miles but passed an MOT about 5 or 6 weeks ago, and the car is serviced anually.

I've had a look at it and I don't think its burning any significant amount of oil - the level hasn't dropped and revving the engine doesn't produce blue smoke, its a light grey colour. The exhaust is quite sooty and if you let the exhaust gas run over some paper whilst revving the engine it leaves a fine mist of soot all over it. Plugs are also a bit sooty but I've seen worse.

I've checked everything I can see on the air intake side and it seems fine - air filter is clean and all the air ducts are tight. This seems to point to the fuelling side which is of course all electronically controlled. I'm thinking it could be the Lambda sensor - is there any easy way I can test it?

I've had a look around and apparently the throttle bodies are a chronic failure point on these and cost about £200 for a recon replacement, but the symptoms seem to be misfiring and uneven idling - this car seems to run reasonably smoothly and the fuel consumption is still >40mpg.

Any thoughts on any other checks I could make or anything I might have overlooked?
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Mon 4 Jul 2005 22:15
Micra running rich - Railroad.
Test the Lambda sensor with a voltmeter. If it's just got a single wire then the sensor will usually be close to the exhaust manifold (the hottest part of the exhaust).

Probe this wire with the red multi-meter lead, with black lead to battery '-'. You should read a voltage rising from around 0.1V - 1V and falling back to 0.1V again continously with the engine warm. If it does then the sensor is working properly, and is showing the closed loop rich/lean effect.

Constant short journeys are a very likely reason for an engine running rich and the O2 sensor gets covered with carbon. Try giving the car a real good blast up the road....

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Mon 4 Jul 2005 22:58
Micra running rich - Aprilia
Coolant temp sensor could be the problem (there is a wiring loom mod too - ring the Nissan dealer for parts information).

Throttle bodies can be had for not much more than £100 now. You can fix for free if you're handy with a soldering iron.
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