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Discussion Starter · #21 ·
The lambda seems to have failed the first fast idle test but passed the second one, so the MOT says. Hmmm.

I'm no expert on MOT tests but both fast RPM idle tests look to be conducted exactly the same. Maybe things were hotter the second time around...

As I understand it a lambda responds to the O2 concentration in the exhaust and goes high voltage (towards 1V) when the exhaust is fuel rich as there is little O2 available then - they act like little max. ~1V batteries which work on the difference in O2 between their exhaust gas end and their other end which gets fresh air.

A bit of digging around lead me to an HonestJohn article which says that the MOT testers don't actually measure the lambda sensor output voltage of the car under test, they calculate what it would be (in theory) from the measurements from their exhaust gas analyser.


This makes me wonder whether the lambda sensor voltage MOT failure isn't just an effect of the high CO reading, rather than the cause? In other words, fix the high CO reading and the theoretical MOT lambda voltage will apparently come within limits again? Thinking about it, if they calculate a theoretical lambda voltage using the emissions test data, it kind of is assuming the lambda sensor is the sole factor in emissions whereas as we all know the ECU relies on engine sensor data as well as the lambda to gauge stoichiometric fuel delivery conditions.

After all, the OP has already changed the cat, what are the chances it's still the cat causing the high CO reading?

Still sounds like a sensor problem to me.

By the way, check for exhaust leaks around the new cat, apparently that can alter emissions readings too. Here's an excerpt from the MOT tester forums regarding someone who had failed on the lambda but passed after sealing the cat joints better:

'i think im the tester who tested your mr2 on wednsday test and advised that the catalyst joint had a minor leak of exhaust gasses. this usually causes a high lambda reading and certainly wont help it getting through the emissions. '

So, case in point, there was nothing wrong with the lambda in that case, an exhaust leak made it look like there was.
Thanks nocturnblue for taking the time to help find a solution, I would think if there was an exhaust leak the garage who is working with my car at the moment I would like to think had checked for leaks as he has had the car up on his lift. I do have a Bosal cat which I had fitted but the readings were the same, turns out the lambda was not working, the one on now is supposedly working but still slightly high co, I fitted a new coolant sensor for the ECU but I think it was no good as the radiator fan came on immediately. He thinks he can do something with the feeling using his Dyno/ rolling road equipment but this I find hard to believe as it cannot read my ECU. I am waiting for a Pscan so will then take the car back and hook it up , one garage I phoned said my belt could of slipped one tooth, not checked this as the car runs very well. I like my MG but I seem to have had every problem an MGF can get over a period of time, this has been the toughest one to sort out, I have renewed so much mechanically , the car can pass an mot no bother except for the emissions.
cheers and thanks Dean.
 

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Discussion Starter · #22 ·
Sorry for a delay in response, I have had the vvc at a local garage, I also bought a Pscan to help with live data. The garage has checked the wiring from the engine management fuses under the bonnet back to the ECU, checked the wiring at the ECU, the live data shows that my lambda sensor is not communicating with the ECU, wiring has been checked on the lambda circuit. I have phoned Rimmers to check if I have the correct sensor, this is the second one, genuine part ones. So now at a loss as to what to check next, I have read that it can or could be an earthing problem on the ECU could this be possible? Been struggling since April.
Dean, Shetland.
 

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OK, the lambda may either be stuck at 1V (according to your MOT test data) because:-

(a) it's duff and won't respond to the ECU's fuelling actions (which when it receives a 1V signal from the lambda should lean the mix a bit to get the lambda voltage to flick down to ~0.1/0.2V) *(see note at bottom)
(b) the lambda works but the signal isn't making it back to the ECU which then assumes the safest course of action and keeps the mixture rich
(c) the ECU is keeping the mix rich because it thinks the engine is cold

So, I've never fiddled with the lambda before or its wiring back to the ECU but here are a few thoughts.

It's hard to test if the lambda is working properly under these conditions because the only way to do that is to vary the fuel mix between lean and rich to see if the lambda changes output voltage, but the ECU is in charge of the fuelling so I'm not sure of an easy way to vary the fuelling manually to test the lambdaprobe operation. You could make the engine run rich by squirting some ether or butane in the air intake but it already thinks it's running rich so you'd see no difference! I can't see an easy way to make the exhaust run lean, which is what you want to test your lambda, as that should make its voltage drop to ~0.1V.

I mean, there is a way to do it by making a 0-1V lambda sensor 'mimic' signal you generate via a simple electrical test box attached to the ECU lambda pins, but it's a bit of faff to go down that road.

I think it would be useful to know what you mean when you say the lambda is not communicating with the ECU. What does the PSCAN say the ECU is receiving from the lambda then? Nothing/no signal? Or is it receiving a plausible signal (which should be about 1.0V given your MOT results) but the lambda still isn't reacting to fuelling actions from the ECU?

Also, what is the ECU telling the engine in terms of fuelling instructions?

Also, does the PSCAN say what the ECU thinks the engine temperature is? (i.e. does it think the engine is cold?).

More thoughts: the lambda sensor I believe has a heater. That's to get it to operating temperature from cold quicker. However, if the heater doesn't work, the lambda sensor may not give correct results at idle as it may be too cool (should be hot enough if operating at 2000rpm though I'd have thought). It should be easy enough to test the heater wires continuity.

Have a look at the link below for a similar story to yours.

 

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Discussion Starter · #24 ·
Hi Dean,

I thought I would email as it’s a bit easier to explain things on here than it is by text.

Firstly and unfortunately, the new lambda sensor doesn’t appear to have made the necessary difference to get the ECU to activate the probe and start using the readings coming from it. I haven’t installed the sensor, as I didn’t want to void the ability to return it should you wish to. I simply plugged it into the engine loom, started the engine, brought the live data up on the PSCAN, and used a blow torch to lightly blow past the tip of the sensor. No activation, no change in reading from the reading about that sensor, the same as with the previous sensor.

This now has me really stumped to be quite honest. To date, since the car arrived, I have:

1: Installed the first new lambda sensor you had. This was wired differently to the original sensor, but gave results and readings where the original sensor didn’t. However, the ECU would not activate it and use the readings from it to control it’s fuelling, hence the overfuelling remaining. This was pre-PSCAN, so I didn’t know it wasn’t activating the sensor.

2: Did an emissions test, failed obviously.

3: Spent time adjusting the vehicle side of the wiring to suit the wiring diagram I could find for the MEMS 2J ECU online. Again, this made no difference.

4: Check the wiring for 02 sensor back to the ECU for continuity and resistance. Which checks out fine.

5: Check that the 02 sensor relay (which is inside something called the MEMS relay box) is actuating and giving continuity right from it’s given fuse in the engine bay to the 02 sensor connector, which it is flawlessly. The trigger/coil wire for closing the solenoid also has continuity to ground, but if it wasn’t working the relay wouldn’t close, so it’s fine.

6: Spent further time on PSCAN looking at all the live data options to see if I could find anything odd, which I really can’t. There is talk online of some faults with cam sensors and VVT solenoids possibly locking and making the car run rich/lean, but having read the live data for the cam control it doesn’t match up with that of a faulty car and appears on the surface to be operating correctly.

At this point, there are no fault codes in the ECU, I can’t (although I could be wrong and would be quite willing to accept it) see any data that looks out of place of wrong in the live data system while the engine is running.

Essentially, I think there is a fault somewhere, most probably electrical, that the ECU is seeing but not telling us, that is putting the ECU into it’s fault mode fuelling settings for whatever reason. This is essentially de-activating the lambda sensor so that it can take itself out of closed loop (automatic) fuel mixture setting and run on an ‘emergency’ fuel map which will give a worst case fuelling strategy to get you by/home. What this fault is? I don’t know.

I have tried to strike a balance between spending hours and hours of time on it, and spending not much time but making effective and efficient decisions and diagnosis’ and throwing a couple of somewhat inexpensive (in the grand scheme of things) parts at it. I think without spending hours and hours more on this I can’t take it any further. I’m not confident I can sort it at a reasonable cost, which is what it boils down to at the end of the day really..! I’m also incredibly pushed for time at the moment, I had hoped that it would be a relatively simple fix but for me at least it appears it isn’t. At this point I would rather admit that I am wrong/unable/confused(?) than see you go away with a big bill and be no further ahead.

You never know, this could be something simple that’s making a total fool of me, it happens from time to time as I’m sure you’ll know, but on this occasion I fail to see it!
Thanks for your input nocturnblue, I have pasted on what has been done at a local garage, as you will read he has done a fair bit of wiring checking, it could be as I have just read from the link you sent me that the lambda sensor is just no good, this is the second one of two from Rimmers, genuine parts, xpart which I would presume to be Bosch.
Dean
OK, the lambda may either be stuck at 1V (according to your MOT test data) because:-

(a) it's duff and won't respond to the ECU's fuelling actions (which when it receives a 1V signal from the lambda should lean the mix a bit to get the lambda voltage to flick down to ~0.1/0.2V) *(see note at bottom)
(b) the lambda works but the signal isn't making it back to the ECU which then assumes the safest course of action and keeps the mixture rich
(c) the ECU is keeping the mix rich because it thinks the engine is cold

So, I've never fiddled with the lambda before or its wiring back to the ECU but here are a few thoughts.

It's hard to test if the lambda is working properly under these conditions because the only way to do that is to vary the fuel mix between lean and rich to see if the lambda changes output voltage, but the ECU is in charge of the fuelling so I'm not sure of an easy way to vary the fuelling manually to test the lambdaprobe operation. You could make the engine run rich by squirting some ether or butane in the air intake but it already thinks it's running rich so you'd see no difference! I can't see an easy way to make the exhaust run lean, which is what you want to test your lambda, as that should make its voltage drop to ~0.1V.

I mean, there is a way to do it by making a 0-1V lambda sensor 'mimic' signal you generate via a simple electrical test box attached to the ECU lambda pins, but it's a bit of faff to go down that road.

I think it would be useful to know what you mean when you say the lambda is not communicating with the ECU. What does the PSCAN say the ECU is receiving from the lambda then? Nothing/no signal? Or is it receiving a plausible signal (which should be about 1.0V given your MOT results) but the lambda still isn't reacting to fuelling actions from the ECU?

Also, what is the ECU telling the engine in terms of fuelling instructions?

Also, does the PSCAN say what the ECU thinks the engine temperature is? (i.e. does it think the engine is cold?).

More thoughts: the lambda sensor I believe has a heater. That's to get it to operating temperature from cold quicker. However, if the heater doesn't work, the lambda sensor may not give correct results at idle as it may be too cool (should be hot enough if operating at 2000rpm though I'd have thought). It should be easy enough to test the heater wires continuity.

Have a look at the link below for a similar story to yours.

 

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Ok, we examined all possibilities with lambda sensor. Do we know how engine ECU see temperature sensor? What temperature sensor provides to engine ECU, or what ECU see regarding engine temperature?
 

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I notice your mechanic says he can't find any PSCAN data that looks out of place or wrong, but when nothing seems to explain the problem you have to reexamine everything. The engine is controlled by the ECU depending on a variety of inputs from sensors (lambda, MAP, TPS, engine temp, RPM etc). if those sensors are sending it false readings it may default to a 'safe' state as your mechanic says. You need to double check that all these sensors are sending appropriate signals, within the normal expected ranges, since your mechanic apparently has thrown his hand in.

Or maybe post the PSCAN data here. Maybe also on the T-Bar site which that link I sent you is from. The K-series engine is used on a lot of Lotus/Rovers, other Rover owners on the other forums on this site might have more knowledge.

Also, don't neglect the possibility of an air leak, maybe further up around the exhaust manifold.
 

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Discussion Starter · #27 ·
I notice your mechanic says he can't find any PSCAN data that looks out of place or wrong, but when nothing seems to explain the problem you have to reexamine everything. The engine is controlled by the ECU depending on a variety of inputs from sensors (lambda, MAP, TPS, engine temp, RPM etc). if those sensors are sending it false readings it may default to a 'safe' state as your mechanic says. You need to double check that all these sensors are sending appropriate signals, within the normal expected ranges, since your mechanic apparently has thrown his hand in.

Or maybe post the PSCAN data here. Maybe also on the T-Bar site which that link I sent you is from. The K-series engine is used on a lot of Lotus/Rovers, other Rover owners on the other forums on this site might have more knowledge.

Also, don't neglect the possibility of an air leak, maybe further up around the exhaust manifold.
I am looking forward to getting my car back as I think the problem has got him stumped, as he says time is money. I have a gas analyser and the Pscan , I will persevere on with it. I put in a new water temperature sensor for ECU it seemed to just make the radiator fan come on all the time, cleaned up the old one and it seems to be doing what it should. I still think the problem is to do with the ECU not picking up the lambda.
 

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I put in a new water temperature sensor for ECU it seemed to just make the radiator fan come on all the time, cleaned up the old one and it seems to be doing what it should. I still think the problem is to do with the ECU not picking up the lambda.
I would also recheck wiring to temp sensor to be sure that you do not have any bad contact or breakage which in one moment works and in another does not work properly.
 

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Discussion Starter · #30 ·
I hope someone can throw some light on this, got my car back and put the Pscan on it, it says that the lambda probe is inactive, the o2 sensor heater is on . I will post a photo of the live data with the engine running.
Dean.
Computer Font Screenshot Technology Electronic device
 

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Well the coolant temperature reads 93C so the ECU knows the engine is warm so we can rule out over-fuelling caused by a faulty engine temp sensor (reading cold).

'Stepper Position' presumably refers to the IACV (Idle Air Control Valve). I've no idea what that should be but it looks plausible for idle. The idle speed is fine anyway.

Intake air pressure from the MAP sensor looks about right for idle.

Ambient and Intake Air temp look plausible.

O2 sensor heater 'ON' also sounds plausible as at idle the exhaust temp may not be enough to keep the lambda sensor at its 300C operating temperature.

I ought to admit I Am Not An Expert on any of this so take what I say with a pinch of salt but I believe there are two lambda sensors on the TF - one before the cat, one after the cat. The one before the cat is I think is called 'Oxygen Sensor Bank 1'. It is the one the ECU uses to control the fuel:air mixture. The one after the cat is called 'Oxygen Sensor Bank 2'. It simply checks that the cat is doing its job and may not be used in fuelling control (but I stand to be corrected on this).

Your screen grab shows two different oxygen sensors but the bank 2 lambda sensor has no data, which surprises me as the ECU should be taking data from both even if it doesn't do anything with the sensor 2 data except generate a fault code if it's out of spec. Unless of course it's deliberately ignoring it for reasons of its own...

Assuming though that on your screen grab, 'Oxygen Sensor Bank 1' refers to the pre-cat lambda then that's a plausible looking voltage it's giving out there. 0.49V sounds about right I would think, half-way between lean and rich (~0.1V lean, ~0.9V rich). The actual instantaneous Bank 1 lambda reading should bounce around between 0.1 and 0.9V several times per second (or more, depending on rpm), but only if the ECU is trying to control the fuelling, which apparently it isn't.

I've just noticed that your result of 0.49V for the lambda voltage is exactly what the guy measured with his PSCAN in that link from The-T-Bar I posted a couple of weeks ago on this thread. I would take that coincidence seriously as his problems were exactly the same as yours - he failed the MOT on emissions, he was getting an 'inactive' lambda indication, a lambda voltage of 0.49V at idle (and up to 0.6V momentarily on the overrun after revving the engine) and he cured his problem with a new lambda after he'd already fitted a new genuine MG lambda to try and cure the problem first time around. He finally fitted an NGK lambda and it worked first time!

The line where it reports the 'oxygen sensor state bank 1' as being 'inactive' sounds pretty conclusive that you're running open loop. The lambda seems to be working as it's sending back a plausible voltage but unless the ECU is actively trying to control the fuel:air mix the lambda won't bounce up and down in voltage (the ECU can only control fuelling in hindsight as there's a lag between lambda readings and the next combustion cycle so it settles for wanging the fuel:air ratio up and down slightly between combustions to get a satisfactory average lambda voltage, but this makes the lambda alternately read lean then rich etc).

'Fuelling feedback correction bank 1' is also blank on the scan result. This should be a value near 1 (or 100%) backing up the idea that the ECU simply isn't actively controlling fuelling.

We've got a bit of a chicken and egg situation here as the ECU is not actively controlling the engine fuel:air ratio. This does not necessarily mean the ECU is defective though. As your mechanic said, it may be just refusing to do so because it has picked up something it doesn't like on its sensors (but there are no fault codes, which is weird!). The Bank 1 lambda appears to be putting out a decent voltage but with the scan data you've provided that still doesn't mean it's working. It might just put out 0.49V all the time regardless of the fuelling, which is not correct.

If it was me, I'd try and see if the scanner can log a stream of live data, then if it can try and get a log of readings coming back from the Bank 1 lambda sensor, from ignition, through cold idle, warm idle, and at a couple thousand rpm. We could then see if it puts out a range of voltage. We already know it can get down to 0.49V at warm idle from your current scan results. If it can't log a stream of data, maybe you can write down the lambda voltage as time progresses instead and report back on that. Also...what does the ECU read if you pull the connector off the lambda (I'm wondering if the ECU is designed to simply default to about 0.49V internally if it doesn't get a good lambda connection?).

If the lambda proves OK from the live data test, then since the ECU refuses to go into closed loop fuelling mode (i.e. oxygen sensor bank 1 'active'), despite the fact we know it's reading the lambda sensor (or is it though...?) as it shows on the scan results, and other sensor inputs look OK, and there are no fault codes*, then I wonder if it's not time for a Known Good ECU swapout...however, the guy on the T-Bar tried a new (used) ECU and it didn't help. I still think you may have a duff lambda.

(* there are no reported fault codes, right? There should be in this situation, it's definitely in a fault condition as it's not in closed loop fuelling mode and that's a big no-no).

PS: Long shot here - disconnect your car battery, have a cup of tea then reconnect it, start the car and try another scan. It might reboot the ECU if there's a weird corrupted memory problem.
 
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