Lambda sensor

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Evoman
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Lambda sensor

Post by Evoman » Tue Aug 16, 2016 11:00 am

Question for you learned folks - what happens when you unplug the lambda sensor on an Elise / Exige?

How will the car run? Reason I ask is a stuttering problem at low load and low revs has finally been determined as a dodgy lambda sensor.

A new one was fitted but it seems this new sensor is faulty as it with it disconnected, no stuttering at all, nada, zilch.

It seems to run fine as in no stuttering and crisp low down but definitely feels low on power with the lambda disconnected. I am of course going to get another asap but interested to know what will the engine management be doing with no signal being received from the lambda? I guess I should mention the car is without a cat too.

Thanks

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tut
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Re: Lambda sensor

Post by tut » Tue Aug 16, 2016 11:35 am

Rich has a S1 Exige 190 so will leave it up to the experts.

tut

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Shug
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Re: Lambda sensor

Post by Shug » Tue Aug 16, 2016 11:43 am

/by no means an expert, but...

Lambda sensor should not affect the power at all. It'll only use the sensor when running closed loop - so in the cruise. As soon as you ask for acceleration, the ECU looks at it's ignition and injection tables and ignores any trim the ECU would apply to hit the Lambda target that the sensor is looking for.

The fact that it runs differently with it plugged in and unplugged points to there being an issue in that area, but a dodgy Lambda won't affect power fuelling.

Do you have an Emerald fitted? Do you have the cable to talk to it and get live readings? Would be interesting to see what the ECU is trying to do differently with the Lambda connected and disconnected - whether it's seeing different sensor values (and I mean perhaps on seemingly unrelated sensors)
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kerryxeg
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Re: Lambda sensor

Post by kerryxeg » Tue Aug 16, 2016 1:04 pm

This might not help you at all - not sure what ECU or setup you have, but I had problems with the 190 ECU when I had it fitted, and tried a new lambda sensor with no improvement. I had a remote thermostat, which I believe was confusing the ECU so it was always trying to warm up the car. All was resolved with an Emerald.

I have the spare Lamba sensor in a drawer if it's any use.

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Evoman
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Re: Lambda sensor

Post by Evoman » Tue Aug 16, 2016 3:29 pm

Thanks for the offer though I think a replacement and hopefully correctly functioning lambda will do the trick.

My other car is a BMW and you just jump in that and drive it and it doesn't fcuk about at all with hard to diagnose faults. They do say the best cars are those that hold a certain something aswell as being brilliant to drive are often flawed though those imperfections make them that little bit more special?

Well it's certainly special this little monster, it's testing my patience but it is truly epic.

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Shug
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Re: Lambda sensor

Post by Shug » Tue Aug 16, 2016 4:52 pm

Always worth remembering that the S1 Exige was a development of a single series racer with an engine that isn't really made as a road engine... Yeah, it's based on a the engine out a Metro, but literally the only thing a VHPD shares with a standard K series is the block. Developed on a shoestring as well, hence all the weird faults that need someone who knows them to trace them. Shame, but they are a bit old-school in that they take constant fettling.

As I say, I don't think it's directly a faulty Lambda sensor, but there must be something happening affecting something else for it to make a difference unplugging it.

Lotus just couldn't get away with selling a car like that these days, which somehow makes me like them more...
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Evoman
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Re: Lambda sensor

Post by Evoman » Tue Aug 16, 2016 10:05 pm

Shug wrote:Always worth remembering that the S1 Exige was a development of a single series racer with an engine that isn't really made as a road engine... Yeah, it's based on a the engine out a Metro, but literally the only thing a VHPD shares with a standard K series is the block. Developed on a shoestring as well, hence all the weird faults that need someone who knows them to trace them. Shame, but they are a bit old-school in that they take constant fettling.

As I say, I don't think it's directly a faulty Lambda sensor, but there must be something happening affecting something else for it to make a difference unplugging it.

Lotus just couldn't get away with selling a car like that these days, which somehow makes me like them more...
Yeah definitely loads of character ;)

Interesting what you say. As I understand it when the lambda sensor is disconnected the car runs "open loop" mode which is what it does even with the sensor connected and the engine is cold.

As soon as the temperature reaches a certain point the car runs in "closed loop" mode and the sensor feeds back a signal into the ECU to regulate the fuel air mixture.

So with the sensor disconnected in "open loop" mode, then the fuel/air mixture would be the same as if the engine was cold all of the time. So basically it is running preset maps and isn't adjusting for the fuel as it would normally do in closed loop i.e. normal operating temperature conditions.

So what does all that mean if the stuttering goes away when running open loop? Could it be a fuelling issue? Or a TPS? Or WTF?!

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Shug
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Re: Lambda sensor

Post by Shug » Tue Aug 16, 2016 10:11 pm

Not 100% right. Closed loop doesn't apply when you're asking for power. Basically, closed loop is when you're on steady throttle and the maps are trimmed to hit 14.7afr, which is where a cat works. Hence cats only ever doing anything for emissions on constant cruise.

Hot or cold, ask for power and the ecu ignores the lambda and looks at the fuel maps. Cold fuelling is just a trim number added to the normal fuel map.

So, once it's warm, there should be no difference in how it reacts when your asking for power whether the lambda sensor is connected or not. That's why it's an odd one that disconnecting seems to affect power.

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Evoman
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Re: Lambda sensor

Post by Evoman » Tue Aug 16, 2016 11:48 pm

Aha okay thats interesting. To be honest I don't know it has affected power really, I guess I was not wanting to push the car as I was aware the lambda was disconnected and unsure how that may affect the running of the engine. Perhaps more psychological than anything.

I'm trying to understand this, so closed loop is used for steady cruising and that's where the ECU keeps adjusting to try and hit the magic 14.7 afr. The lambda sensor readings or voltage readings are part of the inputs the ECU receives to adjust fuelling to suit?

So is the term open loop as you say when asking for more power like wide open throttle and thats when the ECU just reverts to its preset fuel maps?

I wonder when the switch occurs from closed to open loop? Just trying to think if that could impact on the stuttering experienced under light load at 2-2500rpm.

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Shug
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Re: Lambda sensor

Post by Shug » Wed Aug 17, 2016 11:33 am

Yeah, that's it, spot on.

Looking at live data on my old Emerald - it was not a very wide window at all that had the car running closed loop. Ask for the slightest amount of acceleration and it'd head back to open loop running. If you've got the standard Lotus 190 ECU, not sure what the crossover would be, but a standard Lambda sensor simply doesn't react fast enough to enable closed loop running in more dynamic situations like acceleration.

They were reputedly never very well mapped. Does yours just have the fixed offset verniers on the cams that Lotus supplied as part of the kit, or does it have aftermarket verniers that you can adjust? I seem to remember people getting decent results with actually timing the cams properly, not just the ballpark offset that Lotus set them up with.

Again though - this is not really answering your specific question about stuttering... I've just heard reports over the years of all sorts of rough running issues that people tried to get to the bottom of, then just bit the bullet and spent the money on verniers, an Emerald ECU and had the thing mapped properly.
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Ferg
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Re: Lambda sensor

Post by Ferg » Wed Aug 17, 2016 1:10 pm

Can't help noticing Kerry has put up his S1 ECU in classifieds. Buy this, prove its definitely not your ECU and sell on (good market), or you've fixed your potential ECU issue and you can build up to an Emerald.

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Evoman
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Re: Lambda sensor

Post by Evoman » Wed Aug 17, 2016 2:41 pm

Appreciate the input folks I really do. It's been a learning curve, interesting to understand more about the fuelling and try to figure out how all this engine management clever wizardry works. It's been truly epic getting to this point but pleased to say the lambda has indeed resolved the issue. It now runs with rude health. To think it could have been a fault with a brand new part that was fitted very recently i.e. the lambda sensor would have been silly surely but it was.

I have since learned of someone else who had exactly the same issue with poor running and stuttering. They went down the Emerald route with verniers and I understand it was set up to not need a lambda and ran great. They then discovered their lambda was knackered and fitted the original ECU and new lambda out of curiosity and guess what, it ran great!

I wish I'd know about that before this epic journey. To be honest the car drives really nice and always has pulled very crisply from low down so I was never swayed to go the Emerald route. I guess if it had other drivability issues then maybe it would have been a different matter. Perhaps as my car was owned by the Lotus MD as a company car the technicians dialled in the cam timing that little bit better, who knows, all I can say is getting to this point has been fairly epic.

The timing is great too as I'm off for a photo shoot with the car tomorrow and a wee article in a magazine. The garage that were immersed in this journey will get a mention and I do believe a bottle of something for their efforts. Wow, what a journey!

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Shug
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Re: Lambda sensor

Post by Shug » Wed Aug 17, 2016 3:00 pm

Awesome news. Weird symptoms, but great that fixing the sensor sorted it. :thumbsup
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Shug
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Re: Lambda sensor

Post by Shug » Wed Aug 17, 2016 3:32 pm

Evoman wrote: Perhaps as my car was owned by the Lotus MD as a company car the technicians dialled in the cam timing that little bit better, who knows, all I can say is getting to this point has been fairly epic.
Just thinking, if that was the MDs car, it might well be the one car that the one-size-fits-all 190 map and vernier setup was set up for!
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Evoman
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Re: Lambda sensor

Post by Evoman » Wed Aug 17, 2016 4:52 pm

Shug wrote:
Evoman wrote: Perhaps as my car was owned by the Lotus MD as a company car the technicians dialled in the cam timing that little bit better, who knows, all I can say is getting to this point has been fairly epic.
Just thinking, if that was the MDs car, it might well be the one car that the one-size-fits-all 190 map and vernier setup was set up for!
Mmmh, it has been mentioned that there may have been some tweaking considering the ownership history. Who knows, all I know is cars like this shouldn't really be allowed on the road with that crazy raucous sound and that spoiler and all that makes it brilliant.

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