Can anyone tell me if the "Mixture correction learning value" which comes up under "parameters" when using MES to read engine sensor values is the equivalent of "Long term fuel trim".

I've been trying to find 'short term fuel trim' and 'long term fuel trim' as I've been doing a bit of studying on my diagnostics and want to explore in practice.

Pugglt Auld Jock said:

Can anyone tell me if the "Mixture correction learning value" which comes up under "parameters" when using MES to read engine sensor values is the equivalent of "Long term fuel trim".

I've been trying to find 'short term fuel trim' and 'long term fuel trim' as I've been doing a bit of studying on my diagnostics and want to explore in practice.

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Deafening silence here then?

I'm particularly interested in fuel trims because ever since we bought Becky she's had a very slight hesitation under load. She cruises beautifully but when you put load on the engine such as when you hit an incline or accelerate gently from 30 to 40 mph say, she has a very slight "holding back" feeling about her. Definitely not a miss fire, just a slight holding back. It reminds me very much of how the SU carb on the old Austin/Morris/etc vehicles would behave when the metering needle wore. The needle would wear at it's base so the engine would run rich when checked for emissions. If you adjusted the jet to compensate for this (for instance to pass MOT) it would idle beautifully but lack power on acceleration because the carb would now, at higher revs, be running on an unworn part of the needle thus giving a weak mixture. This is exactly what Becky feels like. Needless to say Mrs J happily goes round the shops with her and notices nothing!

I'm fairly sure it's a fueling issue hence the interest in the trim values. But I need to check pump pressure too. Mrs J's sister is still staying and I'm forbidden from getting "mucky" until she's gone home so I haven't actually taken anything to pieces yet (I'm longing to see if the MAP sensor is clogged). However she goes home tomorrow so it won't be long now.

Trouble is MES doesn't seem to list fuel trim values as such? I've had a number of very interesting exchanges with Grant at Gendan and he's not sure about this either (and is very interested to see what I can find). His most interesting suggestion is to connect up my VCDS (VAG scanner) and trigger the generic OBD2 program Then click on the "Mode 1 read data" button where I should see a list of all data readable. Fuel trims should come up here if present. Hopefully I'll get round to this within the next couple of days (weather permitting).

Because I'm convincing myself it's a fueling problem I'm particularly interested in the MAP sensor (Manifold Absolute Pressure - it senses pressure/vacuum in the inlet manifold and is quite an "old" way of feeding info for fueling decissions to the ECU) I suspect it may be blocked/partially blocked. This will be my first port of call. Our 169 Panda engines don't have MAF (Mass Air Flow) sensors which are more common these days.

My understanding is that MAF and MAP sensor out puts are used by the ECU to make the main decision about fueling for any given running condition. The upstream O2 sensor then acts as a "trim" to refine it so mixture can be held as near as possible to the stoichiometric (14.7:1 air/fuel?) perfect so that the cat can work efficiently. I've just been reading an article about MAP sensors which highlights that, because MAP's read manifold pressure/vacuum, they can be badly affected by anything, such as a gasket or hose leak (understandably) but also malfunctioning EGR's (Exhaust Gas Recirculation valves) which can upset manifold vacuum particularly and often will be seen as under fueling! MAFs, sensing as they do, the actual airflow into the induction system, are not so prone to react to leaks of this sort. The same article mentions that not all applications using only a MAP have viewable fuel trims!!!

So, Lots of "fun stuff" to do and check out and hopefully something informative to get back to Grant with. I'll keep you all updated on how it goes. This is "ragged edge" territory for me - I'm finding it all very exciting! Anyone with knowledge in this area? do please chip in if you have any opinions or guidance you might like to give. All gratefully received.

Regards
Jock

PS Can't find an EGR on the 1.2 Euro 4 60hp in Becky (2010 reg). Maybe she doesn't have one? My new Ibiza doesn't have one (I was very surprised to learn)

Pugglt Auld Jock said:

PS Can't find an EGR on the 1.2 Euro 4 60hp in Becky (2010 reg). Maybe she doesn't have one? My new Ibiza doesn't have one (I was very surprised to learn)

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Found it. Hiding under the throttle body according to Mr Haynes. Kenny, at the Fiat indy garage, tells me they never have any issues with them - Nice to know where it is though "just in case".

https://www.fiatforum.com/stilo/456249-i-can-not-see-ltft-stft-values-help.html
http://forum.multiecuscan.net/viewtopic.php?t=4059

Thanks very much. Robert G8RPI seems to be saying, as I suspected, that "Mixture correction learning value" is LTFT. Sussexa then shows a screen shot of it which shows the reading as a percentage (which is what you would expect of a fuel trim value of course)

Then the MES viewtopic suggests that Multiplicative (FRA) and Additive (DTV) are actually the readings I'm looking for. I don't remember seeing them on the one, brief, look I've had so far but could have missed them as I've never heard those names before.

So, great, lots for me to look for now. I'm also going to hook up my licensed version of VCDS and have a look using the generic OBD scanner. It should display if the ECU out puts it.

Hoping to try this tomorrow or Sunday depending on weather and grandchildren. I'll give an update if I find anything worth mentioning.

Thanks again GrandePunto PL - I had the feeling I was going in the right direction, your post and links have boosted my confidence to go further now.

At last I managed to get a bit of time to spend with Becky. I'm trying to get my head round what all the Parameters actually mean/relate to/help diagnose. I'm making steady progress and understand quite a lot of it now. I've been trying to see The fuel trim readings (short and long term) but MES doesn't actually list them as such so I've been wondering if "Mixture correction Learning Value" is something to do with them.

Grant, at Gendan - where I bought my MES, is being very helpful and has suggested that I try linking up my VCDS (I also have a licenced copy of VCDS for looking at my VAG stuff) and using it's generic OBD2 reader to see if the ECU can actually output fuel trims and compare the readings with MES.

So I connected up the VCDS and woke up the OBD2 generic program - which works fine on my boy's Astra. Yikes! A number of warning lights lit up/flashed and, most alarmingly, the steering motor gave out a growl like an annoyed dog woken unexpectedly from a snooze! I checked the interface readings and they said K1 and K2 found but CAN not found. When trying to connect the program was saying "protocol ISO 14230 running" but none of the fields were displaying anything. I'm not sure what's going on here and the "growl" frightens me, so I backed out and shut down the program. I'm now waiting on Grant getting back to me with any suggestions - of course all suggestions are welcome?

I then went back to MES and did a scan (my default position when connecting). It brought up a couple of CAN connection DTC's - ashamed to say i didn't note them down as I usually would, and cleared them, so far they've stayed away. I think I was feeling so rattled at what VCDS had done I just wanted them gone! Anyway she seems fine so I took her down the road and back to warm her up and reconnected MES (I'd disconnected before driving) and started looking at that mixture correction reading it was around 2%. If its a fuel trim that's not too bad is it? Then I ran it as a graph and it looks "spikey and busy" like the illustrations of short term fuel trim I've seen in examples. Long term fuel trim, as I understand it, is usually a less busy and smoother trace? Anyway I think it is probably a fuel trim reading of some sort, most probably a short term correction, maybe it doesn't do long term?

During my little "warm up drive" I noticed that the slight "unwillingness" (weak mixture?) to pull cleanly was noticeable climbing the hill back up from Granton Square - a gentle incline requiring moderate throttle application. With this in mind I thought I'd graph a few other outputs just to see if anything leapt out at me. I like graphing outputs as I think it makes it much easier to understand what's going on compared to trying to make sense from a load of scrolling figures. I looked at the pre and post cat O2 sensors first. The pre cat was producing a nice strong oscillating signal between about 0.1 and 0.9 volts just as would be expected. It also increased switching speed with increase in revs, again as would be anticipated. So looks like the upstream sensor is OK. The down stream is a little more interesting. It outputs a nice straight line, as it should if the cat is working, but I understand it should be around the midpoint in actual numeric value - so around 0.5 volts? This one is really "rich", straight lined right up at around 0.9 volts. I don't think this is right?

I was about to go on with manifold pressure and other readings but my boy turned up with his family and I just can't miss an opportunity to play with any of my grandchildren so that put a stop to things. I will be revisiting this sometime soon.

Applying a little brain power, later that evening, to what I've so far found (and I want to know what the fuel pressure, manifold pressure etc, is before being seriously prescriptive). She drives as if it's just a "tad" too lean - cruises lovely but "hangs back" slightly when a moderate power increase is demanded. I'm wondering if this post cat reading is trying to tell me something. I was always under the impression that the post cat sensor was really just monitoring cat performance? Basically straight line cat working, oscillating output cat failing/failed? So It's straight lined - cat ok? - but reading very high which equates to rich mixture? Could this "rich" reading be causing the ECU to drive the mixture weak? bearing in mind that the upstream sensor seems fine? No, doesn't make sense! Could the sensor "fail rich"? Anyone know if the pre and post cat sensors are interchangeable (2010 Panda 1.2 Dynamic Eco Euro 4 engine 60 hp) - I could try switching them over? - If I can get them unscrewed without breaking something.

Ah well, maybe further "bonding with Becky" sessions may be more revealing.

Regards
Jock.