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Discussion Starter #21
As a matter of interest only:

Can you post the exact Bosch/Renault model numbers found on the faulty/original/new sensors - I have in the past found the Bosch guys to have suggested the incorrect heater voltage spec'd sensors as replacements (but on a MB A160 and there the new O2 triggered a code because luckily the ECU monitored heater current and picked up that fact)
Yes absolutely... I'll probably be the weekend before I get time to get back on it... but yes for sure.
 

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Discussion Starter #22
I fitted the new Denso sensor post-cat today. Below is a photo of the 'new' faulty Bosch sensor that I took out. You can see all the part numbers on it [I hope].

I took the car for a reasonable drive today - around 20 minutes or so - and at one point the check engine light began flashing for about 5 minutes, then it went out. Unfortunately I don't have the Solus at the moment so can't check for faults, but on a quick scan of the net one of the comments I noticed was a persona saying this could be due to unburnt fuel in the cat ?
181907
 

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Thanks for the numbers - so the post cat is also exactly the same numbers?.

Yeah I wouldn't want to jump to any conclusions without knowing why the dash was flashing you .............

Could be the O2, cat, etc etc etc.

Chance of unburnt fuel in cat with a working pre-cat O2? ...........imo close to zero.

Really need a scanner's help here - in particular look for stored codes, pre-cat O2 voltages and now once the engine is nice and hot, on a longish trip the post-cat O2 voltages - what is the LTFT and STFT doing? ................... could be as simple as the LTFT for the throttle input range you were driving at, at that stage, were simply way off due to historical reasons so the ECU flashed the dash while STFT was busy giving its corrective inputs to tweak LTFT, and then once LTFT got down to under 20% again, the ECU returned to its expected state of bliss and no flashing lights.

Many other possibilities but I will have callouses on my fingers if you have to type it all up
 

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Discussion Starter #24
Thanks for the numbers - so the post cat is also exactly the same numbers?.
As per Renault, the post-cat and pre-cat are exactly the same part. The photo I posted above is of the Bosch sensor I removed from the car... as you can see it's almost new. I think Bosch make the 'genuine Renault' sensors, hence the part numbers may be the same. They look absolutely identical. The Denso sensor I've just fitted looks different. It has perforations in the element whereas the other two are solid. We'll see how it goes.

Could be the O2, cat, etc etc etc.

Chance of unburnt fuel in cat with a working pre-cat O2? ...........imo close to zero.

Really need a scanner's help here - in particular look for stored codes, pre-cat O2 voltages and now once the engine is nice and hot, on a longish trip the post-cat O2 voltages - what is the LTFT and STFT doing? ................... could be as simple as the LTFT for the throttle input range you were driving at, at that stage, were simply way off due to historical reasons so the ECU flashed the dash while STFT was busy giving its corrective inputs to tweak LTFT, and then once LTFT got down to under 20% again, the ECU returned to its expected state of bliss and no flashing lights.

Many other possibilities but I will have callouses on my fingers if you have to type it all up
Agreed... it's all supposition without access to the data. I do need to get an Android tablet, TorquePro and the ODB device. If I get time this weekend I'll try and get myself sorted out with those. It would be nice to thinking that it could be the fuel trimming correcting itself long term v short term. Let's hope so :)

As always, thanks so much for your help. More to come...
 

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Discussion Starter #25
Just a follow up on how I'm getting on with this... still haven't bought the Torque Pro set up yet, but will.

I've taken the car for a few 20 minute motorway drives since replacing both the O2 sensors and my friend came over again on Friday with the Solus. We set up graphing and ran the engine until it it 96C whereupon it came back down to about 90C or so. Throughout this process, the post-cat sensor voltage never moved from 420mV, not even a single mV. The good news is that I've no error codes or check engine lights but I'm perplexed as to why the post cat voltage is not moving at all. Would this indicate that the ECU is using its own default voltage ?
 

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I would have expected the post cat O2 to have shown some life with your little experiment ...........

Question - do you still have an actual cat and not just an empty can or a blocked off port?

The ECU as far as I can figure don't have internal default voltages to use - its reporting what its seeing or its sick.

If you don't get a dash moan or error code logged I would say forget about it as long as all of the different LTFT values (throttle ranges) are under about 10% and the STFT value is always oscillating around 0

Perhaps check in the Injection computer that dual loop mixture control is present and selected .............. and if it is, that dual loop control is activated while driving when the conditions are satisfied (see blurb I sent you)........personally I wouldn't bother
 

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Discussion Starter #27
Question - do you still have an actual cat and not just a can or a blocked off port?
:D It's a good question. The port's not blocked off - I had the car running at one stage [during the experiments] with each O2 sensor separately removed so I know that's OK. I hope there's something inside the cat bell (!)

Well the ECU was previously reporting 2.5v [pre-cat and post-cat] from the bad Bosch sensor when it was fitted in each location, so what you say makes sense in terms of it displaying what it sees. I did expect [hope ?] to see a fairly constant voltage across the post-cat sensor, just not that constant.

All the other stuff appears to be reasonably OK. I didn't keep a record of the fuel trims, probably should have, but I'm not getting error codes.

Thanks again for this... will do more monitoring when I get myself properly set up. Trying to figure out a reasonably decent and cheap s/h Android tablet to buy now.
 

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ITO theory of the cat's operation ............... the post cat O2 cannot be producing constant voltages with a narrow band pre-cat O2 control system like ours if the system as a whole is working as it should .................

One only gets fairly constant post cat O2 values, if a wide-band pre-cat O2 is in use and a well designed fuel trim algorithm is in use on the ECU.

With our cheap ECUs and both O2 being narrow band, the post cat O2 will always sorta follow the pre-cat O2 - the cat's ability to get rid of the garbage is reflected in the amount of time shift and level shifting you will see relative to the pre-cat O2
 

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Thought since I always carry my AP200 I'd capture the sort of expected behavior of the narrow band O2 pre and post cat voltages on a known to be in good condition Renault engine and cat (only 26000km on both).

22C ambient when I started the engine cold this morning, drove about 2 km only before the post-cat O2 started producing voltages - driving done while ECU in closed loop only and the graphs attached are about 20% throttle use only with me eventually slowing down for a stop street .................. you can clearly see the time shift and level shift characteristic caused by a working cat in combination with simple narrow band O2s on the vehicle


Screenshot_20200203-091223.jpg
 

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Discussion Starter #30
That's interesting... what's the x-axis scale there ?

Another question while we're at it... is the Autel AP200 a good set up ? That seems to work on iOS.
 

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I started driving at 0 so that's around 2 minutes after I set off.

AP200 is Bluetooth - don't know if its going to work with IOS ............I'm on Android .

I enjoy the thing for the small size and features ............ its lacking a proper logging feature though (apart from the small window you see on that screenshot)
 

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I started driving at 0 so that's around 2 minutes after I set off.
Hhmmm OK, the reason I ask is because I can't see the sine wave-esq switching on the pre-cat that I'm experiencing. Is the AP200 in this configuration sampling rather than plotting in real time ?

AP200 is Bluetooth - don't know if its going to work with IOS ............I'm on Android .

I enjoy the thing for the small size and features ............ its lacking a proper logging feature though (apart from the small window you see on that screenshot)
OK... thanks for that.. I need something more sophisticated. Exactly what dongle are you using with the Torque Pro App ? There are tons on Amazon/eBay... but Torque Pro claim that most of them don't work (!)

As always, I'm deeply grateful for all your help and advice.
 

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Hhmmm OK, the reason I ask is because I can't see the sine wave-esq switching on the pre-cat that I'm experiencing. Is the AP200 in this configuration sampling rather than plotting in real time ?
Hmmmmm - I think you missed the fact I was actually driving in real-world conditions and not standing still idling.

You will only ever see a nice looking sine-wave-like O2 voltage when

1)ECU is in closed loop (think not accelerating hard when ECU switches to open loop) and
2)the engine is at a fixed speed and
3)there are no engine load variations (think up/down hill or throttle input)

................... all at the same time. Soon as you hit the road and your foot tells the throttle what you want the engine to do, then no nice sine wave - what I posted is a real-life and expected curve off of a narrow band O2 of an engine under variable load and speed.

That plot of the AP200 is created from real-time values and the graph scrolls through the window in real-time to give you a real short "last 5 second" history of parameter behavior

For comparison, in the morning, I will grab and post an AP200 graph with the ECU in closed loop at idling so you can draw your own conclusions too.



OK... thanks for that.. I need something more sophisticated. Exactly what dongle are you using with the Torque Pro App ? There are tons on Amazon/eBay... but Torque Pro claim that most of them don't work (!)
I have an OBDLinkLX talking to TorquePro with absolutely no hassles as long as the vehicle is reporting pids and is not locked down or disabled by the manufacturer

More sophisticated? ............... well I have a quite a few way more fancy tools but lately I find AP200 or Torque is often all I need - ito logging you will have to go far to beat the power of Torque imo
 

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As promised - a screenshot off of the AP200 with the engine idling about 30 seconds after cold engine start just as soon as the O2 stabilized ................ sine-like graph like this also possible/obtainable on demand at any other chosen constant engine speed with the vehicle stationary (or at the conditions I gave before when the engine is under constant load on a flat road)



Screenshot_20200204-065232.jpg





If you were to use Torque to create the same graph with the OBDLinkLX or any other fast responding dongle you will be able to see a much smoother/accurate trace that actually looks more like a sine wave .................. in Torque you can specify that only a single parameter should be sampled as fast as possible (while all other info is ignored) - this is not possible in the AP200 where it simply ALWAYS will be sampling ALL parameters
 

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Discussion Starter #35
I have an OBDLinkLX talking to TorquePro with absolutely no hassles as long as the vehicle is reporting pids and is not locked down or disabled by the manufacturer
Real quick reply for now... will get back to you on the other stuff a little later this evening.

Is this the device you've got ?

 

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I have an OBDLinkLX talking to TorquePro with absolutely no hassles as long as the vehicle is reporting pids and is not locked down or disabled by the manufacturer
Real quick reply for now... will get back to you on the other stuff a little later this evening.

Is this the device you've got ?

 

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Discussion Starter #38
Thanks so much for that.

Thanks also for all the earlier posts. Yes of course, I wasn't thinking at all about the engine doing something other than ticking over. You're absolutely right, the profiles will be completely different as the engine's run up and under load conditions.
The Autel is obviously not sampling at a high enough rate to be able to plot a more detailed sine wave, but I can see the switching nature of your's at tick over.
Thanks again for this... I'm going to get the OBDLink LX now and assemble the other bits.
 
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