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MS sensors set up clarrification


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It has taken a while but I have finaly got my megasquirt running. It is not running right and has very little power but as has been mentioned numerous times in posts ‘get the basics right first’. So I have some problems/questions regarding sensors that I hope someone can help with. I have searched and read many many treads on this and different forums and seem to get conflicting info!! I am sorry that it is so long but I am a novice and therefore giving a lot of info so that I can get simple answers😊

I’m running MS1 v3 029v on a 3.5V8, full kit bought from Nigle a year or more ago! TS file attachedif required.

Lambda Narrow band 4 wire from Nigle:

I think it is broken. I am getting 9ohms across the two white heater wires so I guess that part is working but when I probe the black wire (which I think is the signal and hence correct one) and earth it on the sensor case and heat with blow torch, I get 0v. So do I need a new one or am I doing something wrong?

Second question on lambda is wiring. I have one white going to general chassis earth. Second white goes to white/purple wire connected through a fuse to the wire leaving relay going to the fuel pump. The black is connected to Blue and goes to 24 on D37. So, does the grey get connected onto the loom ie to one of the black wires going into the D37 plug OR does it get connected straight to the chassis earth?

MAT Sensor from Nigle:

It appears to be working, showing a gradual min 8.9 to max 19.4. However, engine runs better when the sensor is disconnected! Accelerating results in a ‘nothing gap’ before anything happens but when disconnected no gap and engine pulls better! Does this point to MAT sensor failing or maybe something else?

CLT Sensor readings:

Sensor is not new but standard rover part (lucas 73355) so Easytherm should not be needed. The sensor appears to work and the temp moves up gradually but the figures seem off. On MLV it shows the min as -40 and max 50 for my attached log. Ignition on 18.9 and grows gradually after that. I think Fridge mentioned that if it registers -40 it is broken. However, I didn’t know if that meant it always stays at -40? The max temp I have seen it go to is 65 which is obviously very low for a v8! I have bench tested resistance and they are as follows: 20*=2000; 43*=1200; 61*=630; 80*=500; 90*=350. I have found three different tables/figures for resistance in other MS threads and they all differ as to what are the correct resistance figures  for a V8, and none of them match my sensor. I have tried to find where the readings are in the ECU set up but no joy. So, do I simply need a new sensor or is my ECU reading?

Any help gratefully appreciated.


2018-11-06_10.54.59.msl check temp from cold.msl

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Lambda grey goes to a signal ground, I. E. One of the black wires at the db37 plug.

MAT sensor observations says your acceleration enrichment is too little, so with a disconnected MAT you get extra fuel, helping the AE out, by adding more fuel. Leave the MAT plugged in, and tune the AE.

CLT - have you checked your thermoset is working? Checked engine temp with an IR gun to compare? It may be telling you the truth. If you get discrepencies between it and the IR gun, then you're sensor is bad. You could just swap it, but by buying an IR gun you can use it for all sorts of things.

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Thanks for reply and advice.

Glad I now know my wiring is correct for lambda, I guess a new sensor is needed.

MAT - Ok I will look at accel enrichment. It is as per Niggle's standard setings but I will have a look. I have not had a working lambda ever, so no tuning done yet. So I suppose a new Lambda will allow me to start this.

CTL - yes it is working ie increasing as you would expect, but the figures seem in correct as per above discription. I do not have an IR gun, but rather than spend money on it I might try a new sensor first.


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If you have a 4-wire lambda the 2 white wires are the heater (polarity doesn't matter) and the other two wires are signal & ground, usually the BLACK is the signal and GREY is the ground, and they may well NOT be joined to the body of the sensor (there's a reason for having a dedicated signal ground wire!) so measure the voltage across the two wires, not from the body of the sensor (that goes for MAT & CLT too - there's a reason they have 2 pins!).

Also, you may need to get it pretty hot (at least cherry-red) with your blow lamp to register a voltage - and at most it'll be 1v.

Sounds like your MAT and CLT sensors are fine, if it runs better with one disconnected that just means you haven't tuned it right yet and the "error" brought about by the missing sensor is pushing the calculations towards the "right" answer (EG adding more fuel across the board).

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Hi Guys,

A little update and further questions if that is ok.

I left MAT and CLT in as per advice although temp still only gets to 62 (I'm wondering if that has anything to do with following problem). I then checked and changed my Lambda wiring and now have a reading :) However, the needle stays at circa 14.7 the whole time, during driving or reving. Is this normal as it is a narrow band?

Anyway, as Lambda appeared to be working'ish I thought I would try a tuning run. TS will not tune. I have attached the message/warning I got refering to my filter for 'Min CLT' settings. I have no idea what that is/means. I have looked and cannot find it, even to look at what the setting are. Obviously I have not changed anything from origginal Nigle setttings. Can anyone help

My last question refers to my ARF table which appears to be 1) in volts and 2) showing nearly all zeros. I have found another thread which discusses this but does not provide and definitive answers. If I change my settings to a wideband the regular table around target 14.7 appears, but this is obviously not a solution. However, in the tread there is a sugggested table, which I have included in the attached document. Should I therefore  1) simply input these figures   2) are there other figures that anyone know of   3)change table away from volts, if so how?

As always, any and all help appreciated. I feel that I'm so close to getting it running properly. The mountains and mud are beckoning :)






MLV Tuning error.docx

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OK you are confusing a few things here I think.

The auto-tune feature relies on watching the EGO (lambda sensor driven) correction and adjusting the fuel map towards an ideal target. EGO correction (done by the ECU on-the-fly) is only active under certain conditions - above a minimum RPM, a minimum coolant temperature, and a couple of other factors;


And there's good reasons for this to be so.

If your engine never gets above 62c then maybe sort that out - have you got a very low stat in it, or no stat, or one of those restrictor plates instead of a stat?


Next up - The target AFR table (in the ECU) is only for running with a wideband sensor, it cannot and should not be used with a narrow-band sensor. If you understand how NB sensors work you'll understand why this is so.

Using Tunerstudio to tune towards a target table using auto-tune and/or data logs is a legitimate thing but it's a very different thing, so which are you doing?

Next: Your lambda readings hovering about 14.7 is probably not far wrong, but you need to understand that a narrow-band sensor can ONLY tell you when you're AT 14.7, the rest of the time it can only tell you "higher" or "lower" and any numbers on a gauge in TS are absolutely meaningless as there is NO calibration between the sensor voltage and the AFR, only the "switch point" is accurate:


The curve of that graph will vary wildly with sensor temperature, so for example 800mv output could be anywhere from 14.5:1 to 12:1 depending on numerous factors.


Also bear in mind that until you have the basics right there is NO point trying to do this sort of tuning - and nor should you need to! With only very rough ballpark adjustments from Nige's base settings you should be able to get the vehicle starting & running & driving OK before you need to worry about fine tuning. If you go out and just run "auto-tune" with sensors and things out of whack you just end up ruining the fuel map by instalments.

Remember - you can always just tune it like a carb/points setup by the seat of your pants.

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Regarding the CLT, it may have already been done but RV8 standard sensors use a different range to the GM ones that MegaSquirt firmware supports "out of the box". You need to make sure your firmware has been updated with the correct values and THE best way to do that is to test the sensor manually - a pot of water on the stove, sensor suspended so that it's immersed in the water and use a thermometer to create a series of reference points of resistance vs temperature.

I found when I was still messing with RV8 engines that there were quite large differences in temperature/resistance between the different RV8 sensors. 3.5 sensors were different from 3.9 sensors, for example. I always ended up using EasyTherm because at least then I knew that it was right and matched my sensor. It's also worth swapping the sensor anyway as, even with the stock ECU, the CLT sensor was always prone to going out of spec and causing weird running and starting problems. On the hotwire system it was almost the first thing you did when you came across an odd issue !

One thing that does occur to me though, it would definitely be worth double checking the earth connection on your CLT sensor, make sure it's got a decent connection to the ECU earth otherwise you'll always read low - the sensor is only running at 5 volts so it doesn't take much to skew the readings. If your IAT (MAT) is using the same earth you can also end up with a bridge effect where both sensors feed each other, similar to the effect of a bad earth on a trailer where the indicators cause the tail lights to dim. When you unplugged your IAT, did you see any difference in CLT ?

NB lambda sensors are fine for tuning and running, they are not completely linear and you can get decent readings either side of centre albeit quite a small (narrow) range before it falls off the edge. I know WB are the "holy grail" for some but I've never had a good experience with them and never trusted one, not helped by the fact that the early adaptors from innovate were bloody awful and, by all accounts, haven't improved much since ! For longevity and long term accuracy you really can't beat a NB lambda, the one in my competition motor is now 12 years old, it's been drowned in water and mud, it's seen pretty much every extreme of temperature from Scotland in winter to the Australian Outback and never missed a beat. Earlier this month it was in for it's MOT and, while testing the emissions, the tester said it was absolutely spot on and you could see the ECU switching either side of the centre point as I have EGO correction turned on at idle.

NB always tunes by voltage, not AFR and you pretty much just set a switchover voltage. I don't think the AFR table in TS is used at all for true Narrow Band but can be used if you're running a WB in NB 0-1v mode. Tuning in NB gives you a base map and, ideally, you want to end up with a simple NB tuned VE table across the board. You can then start to manually lean it out in cruise positions and increase the fuelling in higher power areas although your throttle enrichment often does most of that. 


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Hey guys, thank you for feedback and advice.

There is a very high chance that I am mixing things up. I read and read threads and manuals and seem to get confused a fair bit. The fog lits and then decends again!

FF, you are correct re getting basics right and I suppose this was my intention in asking the above questions re my sensors. I wondered if the CLT reading would cause some problems and you have confirmed it may. I do not have a clue what stat is in here but I guess replacing it would be a good idea in any event. Dave, I did do the temp v ohms test and the results are above but you are correct they do not match any of the three different values I have found in various threads. The removal of the MAT did not have any impact on the CLT reading. I will however do as sugested and check earths for a learning experience if nothing else but, I think the simple and probably best solution is a new sensor. 

Re tuning, I do understand the difference between wide and narrow band,  but unfortunately did not understand that the arf table was wide band only, doh! Dave, I understand the wide band is the holy grail, but like yourself I am happy to stick with NB, although I don't think that mine will ever be as well traveled as yours! So, I understand that the guage will not show a varying reading, as it is simply either lean or rich, but I thought it strange that it did not move from the 14.7 point at all. So how then do I see if I am running rich or lean as I am driving? Also to clarrify, with NB I cannot use tuner studios to tune? So how then do I do it i.e. auto tune it? Dave you mentioned 'NB always tunes by voltage, not AFR and you pretty much just set a switchover voltage', could you maybe explain how? I guess this is a really stupid and basic question, sorry.

I will get the CLT sorted first but my vehicle is up and running but is down on power when I get to 4th gear, it cannot hold it, so I thought a bit of tuning might help.

FF re the dialog boxes you included, mine are different so I suppose you are suggesting once the sensors are sorted I should change to match?



Thanks again for all the guidance and sorry if I am being a bit thick.



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The CLT reading isn't causing a fault, it's doing exactly what's expected. As long as your sensor is reading somewhere in the right sort of resistance-temperature range I wouldn't obsess about it.

AFR tables can be in a couple of places - in the ECU when used for target-AFR (voltage) with a WB sensor, or in TunerStudio where it can be used similarly OR, with data-logging / cunning maths it can do some calculations either on the data-log or live running to try and work backwards from the switch-point of the NB sensor and how much EGO correction was applied to try and bring your fuel map towards the target AFR map. However, that relies on EGO correction being active. That's how auto-tune works.

If the gauge doesn't move from 14.7 are you sure the sensor is now giving a reading to the ECU? Either that or TunerStudio is choosing not to display it for some reason.

When the engine is running the sensor voltage should come up as it's heated, then it will (ideally) flick/switch from <0.5v to >0.5v back and forth when EGO correction is going on normally, the bottom trace in green shows this normal driving "cruise" scenario, you can see the red trace creeping up & down as it corrects for EGO:



As for the values I posted, it was only to show you the dialogue box, generally the settings your ECU shipped with from Nige should be left alone unless you have a good reason to change it.

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Hi FF,

Thank you again.....

Ok, I will not sweat the CLT, but will check out stat anyway.

Ok, I will leave settings in dialogue box as per Nigle.

Ok, so AFR guage staying at 14.7 could indicate a problem. I have checked previous data logs and the C02 only moves from min 0 to max .02 and Gego stuck at 100%. I had this set to zero when the lambda wasnt connected so I will make sure it is set correctly at 1 and take a run in the morning and see whats what. Thanks for the log to show what it should look like.

'AFR tables can be in a couple of places - in the ECU when used for target-AFR (voltage) with a WB sensor, or in TunerStudio where it can be used similarly OR, with data-logging / cunning maths it can do some calculations either on the data-log or live running to try and work backwards from the switch-point of the NB sensor and how much EGO correction was applied to try and bring your fuel map towards the target AFR map. However, that relies on EGO correction being active. That's how auto-tune works'

1) So I don't have a WB, so for the moment I guess I can ignore everything in bold above?

2) Can you confirm if my understanding of the second half of the above should be either:

  • that I do not have to do anything other than make sure EGO correction is set at 1 and let the ECU atomaticall do its thing and it will perform a continuous tune?


  • when you refer to 'data-logging', does this refer to recording data logging in TS and then pressin the VE analysis button?

3) Also, am I correct in understanding that I do not need a completed ARF table unless I am tuning with a WB? When you state 'ARF tables can be in a couple of places', I cannot find one. Any table in TS or Meggatune is blank. This last part may not be relevant if I do not need one, but thought I would ask the question for clarity.


Sorry if these questions seem obvious but I am trying to get a clear understanding.

I appreciate your patience and help.



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OK let's explain MS's basic closed-loop tuning scheme, built into the ECU:

When you are driving, IF the following are all TRUE, the ECU will begin making adjustments:

  • Engine temp (CLT) above 71C (as seen in the EGO dialogue box)
  • RPM above 1200
  • In YOUR case, kPa ABOVE 100 (which should never happen - you appear to have disabled closed-loop mode)
  • In MY case, TPS ADC reading BELOW 192

Assuming these settings are met, the ECU will then look at the O2 reading:


It will (in your case) wait for 32 ignition events (bangs) and then:

  • If the O2 reading is in the YELLOW section (above 0.510v), it will adjust the calculated EGO correction value DOWN by 1% if it is allowed to.
  • If the O2 reading is in the BLUE section (below 0.510v), it will adjust the calculated EGO correction value UP by 1% if it is allowed to.

It will then wait another 32 ignition events before repeating that. You can see the steps in the bottom red line in my datalog.

In your case, it is allowed to go +/-10% (so EGOCORR value will be 110% to 90%) where 100% would leave the fuelling value un-changed from the fuel map + CLT + MAT calculations. This is the "controller authority" value.

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Thanks FF,

That explains a lot and makes perfect sense now. I was actually mixing things together, as I didn't get that there were two completely separate tuning systems. I thought WB just gave a more detailed and accurate version of the same system. I will re-read some stuff now that I have a better understanding.

I have left all setting as per Nigle, so not sure why it is in closed loop, but I can change that I suppose. I could also change the Active above temp to 50 to trick it into action if my CLT is giving faulty readings, but I will check my stat first as I would guess it would not be wise to have it tuning under incorrect conditions.

Thanks for all the help guys.

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Just to make one point totally clear (and it may be clear to the OP, but it's not totally 100% evident from the thread).

  • EGO Control (or Closed loop) is used so that the the ECU can trim the fuelling as needed on the fly. It doesn't make any changes to any of the VE tables when it is doing this, so in this regard you can have a tune that is slightly off, but the EGO is able to compensate for it, giving you fuelling that consistently hits the target AFR. This is especially useful when you start getting into the effects of air temp (and heat soak) on tuning, but that's for a bit further down the road...
  • VE analyse (Or VE Analyse Live "VEAL") is when you have the laptop plugged in and logging for Tunerstudio to analyse later, or in the case of VEAL the laptop analyses on the fly. This process does correct/adjust your VE tables and the changes will be saved to the ECU if you burn the changes before shutdown.

To disable closed loop EGO i usually just set the authority to 0%.

I am very much a wideband tuning person - my old LC1 is still working after something like 9 years in my road car, however i have a Spartan 2 from 14point7.com fitted to my 90, and when the LC1 dies the P6 will be fitted with the same.

That said, as Fridge pointed out above you can just tune like people would have done with carbs years ago, trust what your bum is telling you in the seat and what your nose says about the exhaust, how does the engine respond and sound when making various changes? It's perhaps a bit more trial and error, but can still work.

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Good post Quagmire!

Worth saying that the "carb method" should always be remembered as sensors can lie - if the thing runs too rich, burns oil, or has an exhaust leak the lambda sensor will read wrong or not at all, it can get coated in unburnt fuel and read "lean" when in fact things are way too rich - you need to trust your nose, ears, eyes, gut, knees, teeth, and elbows... if your eyes are watering from unburnt fuel but the lambda reading is 0.1v, it's not running lean!

I b***ered the VE table in my RRC in one tuning run because I was splashing through puddles, cooling the sensor below its operating point - AutoTune very assiduously tuned the VE table right out of the park and I had to re-load the settings and start again.

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Ok, good news..... there was no stat in there at all...... good advice FF. I have fitted one (82 degrees) and then let it heat up and took it for a couple of runs...... and low and behold CLT now hits the 80's. Further good news is that the Gego appears to be working and it is running better, I even got it into 5th for a little bit :)

Now for the (potentially) bad news. The first run was with original settings and showed the 02 moving a tiny amount from 0.0 to 0.2. On the second run, I changed my settings to match your (Fridge) Open loop mode settings. I didnt actually notice any difference but the o2 did not register at all. Does this mean the sensor is dead??? I have attached the two files if required.

Quagmire, thank you for the clarrification, that clears it up brilliantly. Simple and easy to understand for a novice like me. tks 

So the EGO appears to be helping me move better, but I need to read up on VEAL and figure out what to do there. Alternatively, if my NB is not working, it might be worth spending a bit more on the Spartan rather than getting another NB?


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OK, if your EGO/lambda reading is not reading correctly or at all, you should not have EGO correction enabled as it will be constantly either trying to richen or lean the mixture wrongly!

Did you actually test your lambda sensor / check the voltage because it sounds to me like it's either not working or mis-wired.

You need to understand this - if a sensor reading is wrong, there is NO POINT in doing any tuning as the ECU is not operating with the right information!

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Thank you for advice.

I did bench test again after previous comment, got lambda red hot and used the two pins and not the body housing for earth ie the black and grey but I got no reading on volt meter.

The heater circuit seems to be ok giving a resistance of 9 ohms.

After checking the wiring and correcting it a couple of days ago, i put lambda in anyway. It gave me the reading of 14.7 and I thought that this was a good sign as it did not register anything the previous time I put it in.

But I think each time it keeps coming back to the lambda being broken.

I guess the EGO was not work previously due to temp not getting high enough and as you say, it does now but incorrectly.

So maybe I'll ask Santa for a Spartan 2!!

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