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Running without the O2 Lambda Sensor?


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Fitted a new exhaust to my Starlet EP91 at the weekend.



New exhaust didn't come with anywhere to fit the old lambda sensor. So for now i've just left it unplugged.



Will this cause any problems? It seems to idle and rev fine.



It's purley a track car and will be driven on the road to and from track. Will it cause any damage? And will I see a loss of significant power?


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Wonder if that's why mine idles like shit (4efte) when I swapped turbo kits we noticed mine wasn't connected. Car smells rich but I've wouldn't say it runs badly? Have been told running it without could cause it to run shitty and may lead to bore wash? Hopefully getting it sorted with a new O2 sensor tomorrow.

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Mines the 1.3 4efe NA. The new exhaust is fully decat straight through with one single resonator. I'm not sure if it was an O2, Lambda or Temp Sensor?



Either way it does smell a bit rich. But not a big problem. I'll be driving it flat out 90% of the time! Unless i'm going to lose massive power or cause damage i'm not that worried.

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O2/lambda its the same thing.

the 4efte had a temp sensor for the cat as well as o2 sensor.

Its going to smell a bit different without having the cat in there to filter out crap lol

Ok Thanks :)

So if I run it without the O2 Sensor will that be ok for now? Should I look into getting it fitted back in?

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O2/lambda its the same thing.

the 4efte had a temp sensor for the cat as well as o2 sensor.

Its going to smell a bit different without having the cat in there to filter out crap lol

not to my knowlidge morgey sensor 1 is always 02 sensor and sensor 2 is always bean lambda sensor thats how i was told in the classes donkeys ago

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not to my knowlidge morgey sensor 1 is always 02 sensor and sensor 2 is always bean lambda sensor thats how i was told in the classes donkeys ago

More modern cars run 2 sensors. One pre cat and one post cat. One of these might be classed as a o2 to measure the % of o2/co2 (or monoxide) mix before the cat has done its job and then the one post cat will be measuring a known difference in o2 post cat and then correct the lambda to assist fueling.

But on these cars one is a temp sensor and one is an o2/lambda.

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I ran my car with no 02 sensor for around 3 weeks and my MPG was awful, once i had fitted my new one (broke the old one) I noticed a massive difference in MPG.



I was getting 50-55miles to £10 of v-power, with the new sensor connected id get 70-80miles without even trying! The same driving style in both occasions!

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From my experience of running with and without and using my wideband to see the difference the lambda sensor is used for idle/cruise closed loop trims and when the engine is under load the ecu swaps to open loop control instead (no feedback from sensor). With the oxy plugged in the ecu does run richer in the idle/cruise area of the maps - possibly runs fail safe base settings (bit hard to tell without looking at the tune which isn't possible). With the oxy wired and working the trims do take a while adjust (possibly why the ecu has a constant 12v feed as a memory wire) but they do make quite a bit of difference depending on your atmospheric conditions and the fuel used etc. I'd recommend running one if you can.


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  • 2 weeks later...

a bit dated my post, but nonetheless, a few years back i was driving home and all of a sudden my ep91 felt sluggish and when i checked the "waste of money, cheap, Christmas tree, pretty light" afr guage i realised it was stuck in the "green/rich"....i pulled over, and checked the engine bay to see my 02 sensor wire broken.


drove home with the car feeling sluggish and smelling somewhat of petrol. i reconnected the 02 sensor wire and immediately the car felt better....iirc i was running a JAM ecu at the time



PS--those cheap afr guages are a waste, but it did seem to indicate the car was running very rich and helped me narrow my search...however, shortly after, i purchased a proper wideband afr system


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i know back in the day some guys used to purposely disconnect the 02 sensor in order to run more fuel when they put on bigger turbos.....this method was even more crude than the fpr/fcd system



i suspect the stock ecu goes in to some kind of "safe mode" when the 02 sensor is not detected and over fuels to protect the engine


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