Lean combustion?

[KenS]

Chas54 - Been looking at the 'IAC position' compared to 'IAC stable position'. Wondering what that 'stable position' is, it might be the ECUs calculated target for the IAC and the IAC position is where it really is (or thinks it is). Looking at examples of good plots, those two plots do run reasonably close to each other, whereas yours are about 6 counts or more out when the O2 sensor starts dropping out. Could it be that the IAC calculations have an offset? When the Idle Adjustment screw is set-up in Service mode, I understand that operation is to calibrate the IAC. Could it be that that Idle adjustment needs re-doing, or there is a leak around the idle adjustment screw / rubber bung? I know this is clutching at straws and I am struggling to know if the directions for lean and rich male sense! but its relatively easy and cheap to check this one, at least it would cross another item off the list.
I wonder if there is any Lotus documentation on the finer details of the closed loop system with inputs,outputs, times, limits and dependancies, surprisingly Google AI knows some detail but not enough and can it be trusted?

IAC.jpg

[Chas54]

Chrism

Yes I had checked under the wheel arch inner but there is no plug there . The cable must come into the under binacle area but i couldnt identify it.

I did try a live cable from the battery into the O2 sensor plug 12v and a direct earth via a jump lead from the sensor body to the battery -ve . .As they didnt improve my start up O2 sensor flat line on elanscan just after starting , i took them off .. They are a bit to external to drive up the road with ..

Ive took the earths off at the plenum / inlet manifold just by the power steering reservoir. Ive cleaned them and am just trying to figure how to get them back on . There's not much room even with Reservoir bracket undone .. Ive just lightly brazed a gas welding rod to the bolt head thinking i can get the bolt through the cable eyes and then into the hole and slip a ratcheting ring spanner down the wire.

With your suggestion , I think i might have to revert to my original plan and replace the O2 sensor plug with a chocolate block connector and run a new feedback wire to the ECU and join at the cable there.
Also bring an internal cable from the battery directly to the chocolate block with a 12v+ and a -ve . If i can prove this cures the O2 failure just after start up i can than do an on road test without to many cable outside the car ..

Just at the moment Ive ended up with the coolant header tank outlet hose leaking at the header tank end, Only slightly at the moment but the hose end is pretty ancient And the ends are different sizes which makes it awkward to find a replacement. Dont want to flood my coil and ignition modules.

Thanks for advice Chas 54 .

[Chas54]

Kens

I did adjust the IAC in service mode just after changing the thermostat and CTS . I ended up with about an eighth of a turn further open and at idle, a 20 count.
I do have an old IAC valve with a damaged (marked ) valve head . I cant make it work on the bench. As far as i can tell t has two coils and looking at the ECM drawing the pins are at 12v . Im guessing its an open coil and a close coil . Ive tried energising the coils from a battery but they dont move. It could be this IAC is faulty but i was just trying to figure out how they work and how fast.

Thanks for looking and advice

Chas54

[dapinky]

Okay, here's a completely off-the-wall thought........

..... what would happen (or would 'we' expect to happen) if you were to unplug the O2 sensor which is fitted to the car, and plug one of your spare ones into the socket at the wing...... and simply cable tie it somewhere out of the way (earthed if necessary) so it reads ambient air.

I fully appreciate that ambient air won't get the car running 100%, BUT, it would be a 'constant' reading (ish) - and it may help to establish if the sensor still drops out at any point when it is independent to what is actually happening with the combustion mixture.....

...... or would this not help as the sensor won't be exposed to the same temperatures????

[KenS]

Dave - I would vote for the external O2Sensor to read a steady 0.1V due to free air being a lean mixture (provided it reaches temperature with its heater, maybe steady 0.5V if not) and the car will run in OpenLoop since it cannot see an oscillating O2 voltage to trip it into closed loop. Would be interesting to see what it actually does.

[KenS]

Chas54 - have you had a look at the spark plugs recently? Do any show signs of running lean?

[chrism]

That's great because if they do show signs of running weak it'll (also) solve the issue of whether the EScan graph showing closed loop and/or a:f ratio is actually a measured quantity or merely an 'association' or target that's thrown up when the O2 sensor had awakened - even though it falls back to sleep . Then it's a case of looking for extra airflow?

If they're a normal colour then it indicates an O2->ecu connection problem (with some temperature dependency...)? (I thought all m100s had that wheelarch m/plug connection?)

I feel your pain Chas54

[Chas54]

Ive cleaned the earths at the plenum with a dremmel wire brush and eventually got a piece of 6mm studding into the tapping. I gave up with the set screw and settled for the studding with a cable tie to get it near the hole, and with 2 nuts locked on one end managed to get the thread started with a 10mm ratchet spanner with a flexy elbow. ,

I tried a warm uo but it was running really rough and i tried the spare O2 sensor plugged in but not fitted to the blower. Supported it in a baked bean tin wiith a welding gauntlet wrapped over it sat on the blower.

I googled the operating temperature and its works at above 300c , As the car was running so rough it didnt really prove much but during a period i did see 2.0 v on elanscan whilst it was plugged up.

I went back to the fitted O2 sensor and plugged it in and eventually got a reasonable idle. I saw an IAC reading of 127 counts at one stage , highest ive ever seen.. But once idling steady and around 98 c i switched to service mode and adjusted the idling speed down a little , the IAC control screw is now fully closed which may indicate I do have air getting in somewhere.

I have checked the plugs today and if anything they are only very slightly lean I think . See photo attached .

plugs2 resize.jpg

I still think there's value in trying to get the external O2 sensor to operate as a test to prove the wiring . First i am going to fit cables from a battery on the work bench and see if i can get it hot enough to operate. Checking the feedback voltage looks sensible .Then repeat on the car but unfitted,

The elanscan trace is here but its not really worth examining in detail as i was struggling to keep the engine running initially and i was swapping the plugged in sensor at random

after cleaning plenum manifold earths.zip

Thanks again to all for suggestions and advice

Chas54

[chrism]

Those plugs don't strike me as showing a particularly weak mixture; they look a normal colour to me.

What do others think? They may not have been subjected to many miles of weakness tho'. Hard to sasy...

[KenS]

Agree that the plugs look normal, so inconclusive on that one.

externalO2.jpg

The plots make some sense, but I cannot see any clue to any root cause.
The center period 440sec to 1700sec look like its running with the fitted O2 sensor and displaying the same characteristics to previous plots.
From 1700sec to 2090sec it looks like the external O2 sensor it connected but maybe with a struggling heater, when its too cold its near 0.5V (not at operating temp), when hot giving near 0V (lean free air) OR if there is a missing earth reference back to the ECU for the sensor the ECU could be seeing the floating voltage (0.5V?) as 0V. With this set-up I guess its difficult to maintain a good earth on the external sensor body.
When the ECU sees an edge or two on those changes from 0V to 0.5V it does try going Closed loop but drops out after a few seconds because its not a continuous oscillation as expected.
Not sure why the IAC goes so high on those first couple of starts
So again the plots seem inconclusive, they havn't ruled out intermitancy on the O2Sensor heater or its signal/earth! (but gut feeling is these are OK).
That Idle adjustment screw is niggling! Have you had it at the stage where the engine is up to temperature and can switch 'service mode' in and out and the idle remains steady at 950rpm? Does the adjust screw have the rubber cap over it?

I will have a go at getting a plot of my car tomorrow, by having ignition ON, Elanscan logging but not start the car. Thinking will this record the O2Voltage (effectively in free air) with just its heater on. If it shows a nice plot of starting at 0.5V which then does or doesn't go down to near 0.1V, it could be used as a reference plot. But I suppose we know that yours does have the connections giving valid plots at times it's determining if there is an intermitancy thats key, but a plot may just help overall understanding
So is it still :
1/ Is the O2Sensor intermitant in either heater or signal or earth
2/ Is the O2Sensor indicating a valid lean condition?

I have a ColourTune somewhere!

[chrism]

Ken two things:-

Firstly I have a trace from my S2 pal's sickly O2 sensor that shows closed loop normal, a:f ratio 14.7 yet O2 sensor lean all at the same time. The fact that there is some oscillation might be 'setting' a closed loop and an a:f of 14.7?



...which means that we might be being misled by closed loop and a:f of 14.7 being associative to the O2 sensor reading a voltage - any voltage in fact(?) - rather than an actual reading.

Is Chas' O2Sensor indicating a valid lean condition? - possibly not? Possibly closed loop and a:f ratio too, I wonder?

Secondly being a converted SE Chas' O2 sensor has been updated out-of-the-factory, as has mine. Yours is an S2 wired up 'proper'. Would it be an idea for me to mimic your ign ON engine OFF recording of O2 voltage/free air plot just in case your S2 wiring isn't as typical of Chas' car as mine is? (Just a check on variability...)

ps like you I think I can dig out a ColourTune and I can raise you a Gunson Analyser sad innit?
pps I'm thinking that if Chas can wrangle the O2 sensor to oscillate continuously then closed loop, no sensor lean and 14.7 should all 'play nicely'?

[dapinky]

ps like you I think I can dig out a ColourTune and I can raise you a Gunson Analyser sad innit?

I'm a bit posh....... I certainly have a Colourtune...... but my Gunson exhaust analyser is the digital version, not the 'common' dial gauge one that it replaced!!!!! - and I've still got cars that they are useful for.

BUT

Back to the issue.... with the 'loose' O2 sensor maybe not getting a good earth, the options I can think of are either to obtain an M18x1.5 female threaded part (either an aftermarket O2 exhaust boss, or a nut) and actually build a housing with a decent earth to the car...... or maybe wrapping a good length of MIG welding wire tightly round the threaded portion, and then going to a good earth would do?????

[KenS]

Chrism - I have done the 'good' example plot for just the ignition On and car not running:

just ignition.jpg

6-9-2026just ignition.zip

It shows the O2Sensor voltage at constant 0.45V, i.e. it cannot be getting warm enough to start measuring Air/Fuel ratio otherwise it would have dropped to near 10mV to indicate a lean mixture with Air/Fuel ratio >> 14.7.
It also shows that it does not enter Closed loop, I guess because the engine run time is still zero. The Air/Fuel ratio shows a value (not a target value of 14.7). but since its not up to temperature that value is probably nonsence.
Not sure if its of any value since it doesn't go into Closed loop as it should with engine running.

Good point about the O2 Sensor Lean Flag, I havn't looked for that in most plots, I have been focusing on the O2Sensor voltage when it goes down to near 0V. More things to look at and understand, when they are valid and if they change validity when going from Open loop to closed loop.
I think any rising edge on the O2Sensor voltage will cause the ECU to go into Closed Loop, and will blindly display the Air/Fuel ratio at 14.7 (as the target), if the O2 Sensor voltage stops oscillating then the ECU drops out of Closed loop and starts displaying an 'actual' Air Fuel ratio, but I think that 'actual' must be an ECU calculated value because there is no direct way in measuring it as in the case of an SE Elan or a failed O2 sensor. Plus, during initial warm-up of the engine, the rules are a bit different, looks like the ECU will keep it in closed loop even if it is running lean or rich, I guess at cold the magic 14.7 is not actually ideal so the ECU has to allow a wider range just in that warm-up period.
Still learning and hard to know for sure if the picture is correct!

[Chas54]

Ive had my two other o2 sensors on the bench and cabled up to 12v battery . I did cable the earth to the O2 sensor body with croc clips . On the car I have used a jump lead from the car battery -ve to the O2 sensor body so I think i get a good earth.one with resistance 5.2ohms and the other 14.8ohms.

On the bench its really difficult to get up to temperature . Ive got a remote thermometer to point at the O2 sensor sampling end . I cant really get a realistic voltage reading . 0.023V at 30C, and 0.019v at 80c.
Ive raised the temperature by using an electric hot air gun to 136c with a 0v reading . It may be working as expected as low voltage for lean mix . But as the operating point is suggested to be 300c + , i don't think the test is realistic . Leaving the O2 sensor powered up on the bench doesn't raise the temperature enough to cope with the natural air cooling .

I have found a gunsoms gas analyser that i bought years ago , So this afternoon i may try warming the engine up again and i expect i will be able to see the O2 sensor working on elanscan and see what the combustion is like with the analyser. I agree with the diagnosis of the plug colour being normal.


One thing that always concerns me is the lack of knowledge i have of the learned memory function . Its part of the engine running set up that is captured during normal driving. Loosing it by battery disconnection then requires it to be re written in normal use . Until that i think the memcal has an installed standard set up that is used in open loop. I wonder if i need to persevere past the terrible running and capture some engine specific data to the learned memory.??

Thanks again for all the comments and suggestions

Chas54

[chrism]

I don't know too much about the m100 ecu but I agree there might be a need for 'mileage' while the various sensors find their natural positions.

I used to have an MGTF135 which was reckoned to need ~200mls of normal motoring to get 'centred' - tho' I'm not sure that it'd affect the start-up of an O2 sensor?

[Chas54]

Ive Tried another smoke test looking for air leaks but cant find anything unusual.

I blow the smoke in fia the MAP sensor fitting on the plenum end. leaving the MAP disconnected .

The smoke is blown through the generating jar via an air line at low pressure. I disconnect the air inlet to the plenum throttle body and cover this with a surgical glove zip tied to the opening. The glove inflates and i try to find any smoke.

There was a little passing through the oil seperator on the cam cover by the water pump and CAS , it passes in to the air pipe just before the air filter, One of the two little hoses.

There is also some passing the throttle plate as even with a plug in the idle air take off at the bottom of the throttle inlet , i could see smoke passing . The throttle is on the external stop screw , though and i am loathed to tamper with this ..

After this i tried an ignition on whilst i had my meters attached to the O2 sensor by slipping up the sides of the cable seals.
when the ignition is on , and the engine not running , there is no voltage supplied to the O2 heater . I had a jump lead to earth from the the O2 body tp the cam cover vent.


Only once the engine is running , and the ignition warning light out , does the heater start working. The elanscan show my typical short set of spikes then a drop off of sensor generated spikes for a few minutes .
Once running warm and the O2 producing voltages, I switched to service mode at about 990secs engine run time. Opened up the fully screwed down IAC by pass screw to about 3/4 turn.
Switched back to normal at around 1170 engine run time.

The gunson gas meter is indicating between 1.3 and 1.7% CO.

At 1730 engine run time i removed the jump lead earth from the CO body and about 1800 put it back on. It made no perceivable difference ..

The 14.7 air fuel figure must be a target as it is stoichiometric perfect , no excess air or CO in the exhaust. 14.2 and 14.3 i saw at times on my elanscan would indicate slightly rich at those times and correspond closely with my 1.3 to 1.7% CO.

As i have now opened up the IAC by pass a little , and am therefore letting more air in at idle, the IAC valve has pulled in to 16 to 17 counts at idle to compensate. I wonder, does this signify that my smoke test and seeing the leak round the throttle butterfly plate show that i have too much passing there?? Too much air then cooling the sensor plate?

Of course this doesn't explain my scan showing the O2 sensor working initially then stopping , then starting again. During this dormant period the volt meter across the sensor feedback showed the output as 0.04 and 0.05 although elanscan shows 0.2v , maybe that's the lowest it will register. The heater was still powered up and measured on th the O2 sensor side of the plug.


Ive attached the elanscan from today and after yesterday , i was surprised how well the engine ran..

Again any comments welcome.
My next step is to go out for a spin and consider removing the throttle body to see about closing the gap.

after smoke test and gunson gastester.zip

chas54

[chrism]

Just a thought...I've never been aware that anyone's made a point of removing their CO pot as part of an SE -> 1499 upgrade since the O2 sensor bypasses it. I wonder if that's affecting the O2 voltage scan?

Never having done it myself, is it easy to whack it back in and see if that affects the issue? (Since plugs, driving and gas tester show 'good'?)

Another thought, I wonder if a prev owner has replaced the alternator? A while ago there was a bit of a kerfuffle when one of our major suppliers was supplying alternators whose regulators weren't capable of supplying a good enough heater voltage for the sensor. Of course few initially suspected the issue since the sensor would eventually start up by exhaust gas heat. In this case tho' the red light stayed on...

[chrism]

Another thought when mine depinned it still read 1499 in EScan.
I'm wondering if your ecu jumper is okay (if you have one?) cos if you're defaulting back to open loop, 1499 wasn't working and you haven't got a working CO sensor who knows what the ecu would be trying to serve up?

[Chas54]

Putting the CO pot back is an easy option for a test . I found my old one in the box with the old ECU.. I'll check the range for resistance and put it somewhere mid point before plugging it back in.

I don't know what the ECU jumper is so i'm assuming I don't have one ?

I think the alternator is good as the voltage to the O2 heater is steady around 13.5v . From memory i think the bulb is in the excitation circuit for the alternator , it has to illuminate to cause the iinitial excitation of the electromagnets but goes off after the alternator can support itself , although the line remains live .


thanks

Chas54

[chrism]

Ah sorry - you've got a new 1499 ecu rather than the RonR upgrade in your original that I assumed you had...it's in earlier posts

Yep I'm wondering if some of the old CO pot circuit might be significant in making your sensor swing consistently. I'm not sure the actual setting would be that important, so mid-value should be okay...