Reading live data.

[023sbarn]

Hey guys, newbie here.
Im currently having mpg issues with my clio 182. It just wont go any higher than 28mpg even with motorway driving.
Im going to check the tyre pressures and swap the lambdas round incase the pre cat lambda is faulty. I know the brakes arent binding and its recently had a service.
Im going to plug it into my boss's diagnostic computer tomorrow to see if it brings any faults up.
Im also going to have a look at the live data but i literally have no idea what im looking at.
Ive tried searching on here and it looks like i should be expecting 100mv - 800mv from the pre cat lambda sensor?
Apologies if this doesnt make any sence, Ive also read that the coolant temp sensor can cause issues, im guessing that on the live data, it should be reading the same as my temp gauge in the car once the engine is warm?
Any ideas or help would be greatly apreciated
A

 

[Dan@SJM]

My money is on timing. That's the figure they always produce when the timing is out.

 

[Steven103]

I'd be following Dan's advise waaay before my own, but regarding lambdas in general...

As you say precat lambda reading should alternate between 0.2v and 0.8v ish several times per second. The exact voltage and the number of times it switches from high to low per second depends on the health of the lambda sensor and importantly the quality of your data logging kit. CAN data via OBD is slow at the best of times, so by the time you add in a cheap Bluetooth dongle, a mobile phone and an app you might find the screen only updates once every two seconds - potentially a problem if the lambda signal is actually switching 3 times a second.

There is a BS-EN/ISO/DIN (can't remember which) standard for Lambda sensors which says they should switch from high-low-high a minimum of once every 4 seconds. So you could use that as a reference. A poorly lambda is usually quite obvious though: it could switch very slowly or irregularly, it might only go from 0.3v to 0.55v, it might "flat line" and just look dead for a few seconds etc.

 

[Steven103]

Just read this, since writing that ^^^

Nice picture of what a brand new lambda sensor on decent diagnostic kit will read like http://www.cliosport.net/threads/my-182-general-maintenance.759345/#post-10554405

 

[023sbarn]

Right ok lads thanks so much for the help. Il plug in the diagnostic equipment tomorrow and see what sort of figures ive got. The cambelt and dephaser need replacing early part of next year anyway so i think il change the timing belt sooner rather than later, see if the timings out at all and go from there. Thanks again.

 

[023sbarn]

Ran a diagnostic check on it today, no faults found,
Heres a few figures from the live data
pre cat lambda reading 68mv - 692mv Fluctuating well)
post cat lambda stays at 409.92 mv
water temp 86*
manifold pressure 1046 mbar
air temp 48c
idle 800rpm
throttle postion 3 degrees.
idle reg
idle regulator valve opeing 29%

As i said, im not so clued up with live data but i read that the pre cat lambda should read from 100mv - 800mv.... where as mine goes as low as 68mv? would this cause fuel issues seeing the voltage drop as low as that?

 

[bashracing]

pre cat lambda, is that at idle or in motion?

 

[023sbarn]

thats at idle

 

[bashracing]

not a million miles out tbh,
put it on a mot emission tester to see if it's over fueling
if all ok it has to be resistance from tyres, driveline etc

 

[Dan@SJM]

I'm still saying timing.

 

[bashracing]

dan has a lot more experience than me with these, so he's probably right
with the belt due replacement, could stretch in the belt knock the timing far enough out dan?

 

[023sbarn]

Il be doing the cambelt in january, i just wanted to carry out every other check i can before then so i know everything else is in good working order.
Its literally just had an mot and passed on emissions. When i say the mpg doesnt rise over 28mpg on the motorway, im only doing about 3 miles on the motorway on my run to work and the rest is town driving. Ive read about doing the acid test, holding it for 65mph on the motorway for 10 mins and see what sort of mpg i get. Im doing a 50 mile motorway drive on saturday so il check it out then and report back.
Also getting to work early tomorrow to swap the lambda sensors over so il see how i go.

 

[Dan@SJM]

dan has a lot more experience than me with these, so he's probably right
with the belt due replacement, could stretch in the belt knock the timing far enough out dan?

Nah, I reckon this will be out on the crank, put in the balance hole I reckon.

 

[023sbarn]

Got it sorted. Turned out to be a faulty pre cat lambda sensor. I swapped them over before i started to work, reset my trip and got an average 35mpg. It even went up to 37mpg at one point (drving like a grandad the whole way home). I cant believe it, it was only out a fraction on the live data. I guess it just goes to show, if its out of the 100 - 800mv mark, even just a little, then itl cause issues. At least im a little wiser with reading live data now. Thanks so much for the help guys, greatly apreciated!!!

 

[Dan@SJM]

How slow was it on live data? You shouldn't see it working up and down the voltage, it should be almost flicking between the upper and lower voltages

 

[023sbarn]

yeah it was flicking through the voltages pretty quickly. It would flick through like... 68 - 762 - 104 - 700 - 90.
I thought aslong as its going from high to low (with in 100 - 800mv) then it should be fine.
and it was fluctuating between low and high voltage like every second.
I used autel maxisys to get onto live data. First time ive used it for it.