Mercedes C class w204

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i860
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Mercedes C class w204

#1 Post by i860 » Thu Dec 06, 2018 9:52 am

Hi
First, thank you for accepting me on this forum.
I have a Mercedes C class 280 w204 m272,v6, 240hp from 2008 converted on lpg. Agis p13 obd can iso, barracuda injectors, kme gold reductor.
I have a few small problems and I really want to find the answer.
The car is running ok on lpg the stft and ltft are in the limits as per my pic1.
The first problem if enable the "obd on" option in the program pic 2 i have this error pic 3 ( the program is in demo mode not connected to the car ). Seems like am communication error is there something that I need to install to make the fuel pump not trigger this error?
If the obd is off then there is no error.

The second one ( i know what you gone say, don't use the option ) is related to the obd on + enable obd correction pic4. If this option is enable the lpg switch console will not go to sleep, the B button ( petrol ) is always on and overnight my battery will be drain. If the option is not enable the console will switch off after 1m when you take the key from the ignition.

And the last question
I did update the ECU software and the LTFT is changing like the STFT. Before the update the LTFT will not change as fast as in the video, have you seen this kind quick change of LTFT on others car?
https://www.youtube.com/watch?v=qnwHM-oUZzw

I attached the pics on this lnk
https://imgur.com/a/Pu8Jzrn
pic3
pic1
pic2
pic4

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Re: Mercedes C class w204

#2 Post by LPGC » Thu Dec 06, 2018 10:38 am

No time to watch videos etc this morning but seems to me you've explained enough in words to know what's going on.

Don't connect to OBD, especially not on a Merc. The connection interferes with the vehicle canbus and can cause all sorts of problems due to preventing the vehicle's various ECU's talking to each other (or at least messing up some time critical canbus interactions). For example, can stop the engine ECU talking to autobox ECU properly leading to harsh auto gear changes, can even prevent the engine starting as it interferes with the engine ECU coms with the body/immobiliser ECU. I know of a few people who started to suffer some of these symptoms so drove around with a scanner plugged into the OBD socket trying to trace the problem -when I told them to unplug the scanner all the problems went away!

Fuel pump error could be actual when running on LPG, in which case it would probably be because the car needs a fuel return fitting (I'd have to check on this but lots of 2008 Mercs do need a fuel return fitting - and unless one is fitted you stand no chance of calibrating the LPG system properly). Or, could be another canbus issue, fuel pump control module might not be able to communicate properly with the Bcm/Petrol Ecu with the LPG ECU or a scantool connected to OBD... Ironic that in the case of the scantool it's checking for problems that can cause a problem! Or, could be an actual fuel pump, pump control module or fuel pressure issue.

The OBD connection can also keep ECU's awake - when the petrol ECU gets a canbus signal it powers up the engine's positive feed (to injectors, coil packs, etc), which if the LPG ECU is wired in the usual way to sense ignition on from petrol injector positive keeps the LPG ECU awake, then you get the latched condition of petrol ECU and LPG ECU keeping each other awake. You can usually prevent this problem by wiring the LPG ECU ignition on wire not to petrol injector positive but to something else that might only be live when ignition is on (such as maybe a fag lighter socket). In light of the above problems though, which this won't fix, this doesn't really matter because you won't want to connect to OBD anyway.

If Stft max/mins out (say +25% / -25%) the petrol ECU sees this as a fault condition and won't steer Ltfts. But if stfts were/are all good running on LPG there could be another issue preventing ltft steering and might guess that a couple of such issues would be if a canbus fault or fuel pump fault is detected.
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i860
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Re: Mercedes C class w204

#3 Post by i860 » Thu Dec 06, 2018 11:50 am

Hi, thank you for taking the time to read my post.
The w204 is my wife daily car so I am not playing as much as on my car but I monitor LTFT very often. With the engine, off and ignition on I can read it properly.
Also if i was needing a return you said i will not be able to calibrate correctly, as you can see my ltft is ok on both banks.

I have a Mercedes slk 350 on lpg, same lpg ecu same injectors.
This is on obd on + enable correction since 3 years and no problems, as i play a lot with this car. The only problem is when scanning the car I have to disable obd from the lpg ecu.
Also, I install a fancy lpg switch so I don't have to plug any obd tool to read the stft and ltft.
https://www.youtube.com/watch?v=3m0DmWfitGs

I know a lot of people don't like the auto correction but in my case, on slk 350 I found this option ok.
I dyno the car on petrol, LPG with correction off and lpg with correction on. With obd correction off I was 9hp down comparing to petrol and with obd on I was 5hp down comparing to petrol.

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Re: Mercedes C class w204

#4 Post by LPGC » Thu Dec 06, 2018 3:14 pm

The canbus problems I referred to will only occur on certain affected Merc models, good if they don't occur on the SLK but maybe they are occurring on the C class. You have to disable the LPG OBD connection to read trims with a scan tool because the LPG OBD connection is extra traffic on the canbus, the extra traffic can cause problems on some Mercs of vehicle ECU's not being able to communicate with each other properly.

On your SLK, if the system was calibrated properly there's no reason why it should make any less power than with OBD connection enabled.

How do you read LTFT's with engine off and ignition on?

Still haven't watched any of your vids, will when I get time, but can imagine what the content.
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Re: Mercedes C class w204

#5 Post by i860 » Thu Dec 06, 2018 8:26 pm

Hi
For reading ltft on w204 i use an elm327 with android phone.
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Re: Mercedes C class w204

#6 Post by LPGC » Thu Dec 13, 2018 10:37 am

You need to read trims with the engine running, not just at idle but over a wide range of engine loads and rpms. Stft's will always be 0% when the engine is off, if stft's remain 0% when engine is running it will be because the engine is running open loop. Can you set your OBD reader to show if each bank is running open/closed loop at the same time as showing fuel trims?
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Re: Mercedes C class w204

#7 Post by i860 » Fri Dec 14, 2018 1:25 pm

Hi
I know stft is 0 with the engine off.
I was referring to the LTFT.
When I do the lpg map yes I watch the stft while driving in different loads injection time etc, and I try to bring it as close to 0% on both banks and -7% to -10% under heavy load and kickdown.
After I update the car ecu me9.7 the readings for the LTFT changed now if I drive the car LTFT is changing very fast like the STFT as per my video.
For me, LTFT will give me an idea if my car is tuned ok on LPG.

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Re: Mercedes C class w204

#8 Post by LPGC » Sun Dec 16, 2018 4:58 pm

Just watched your video.

When calibrating you don't just watch the sftf, you need to watch the ltft and stft. The stft's steer the ltft's over time, there are many ltft's each covering a range of combinations of rpm and engine load, if you change either the rpm or engine load the petrol ECU is likely to start applying a different ltft (the ltft that corresponds to the new rpm and engine load combination)... Everyone who calibrates using the watch the fuel trims method needs to watch ltft's.

It is likely that the trim readings on screen are slow to change because of the speed of the OBD connection to the vehicle, usually you'd see the stft's change quite quickly and the ltft's change more slowly... The speed of the connection can lead to a distorted view of the actual fuel trims that the petrol ECU is applying.

The W204's started production in 2007 so will run a sequential fuel system but the injector duration readings in your video point to a full group injection system. I have the Agis software but the software will not open without being interfaced to an Agis LPG ECU and I don't have an Agis system here to interface it to. Agis is seldom seen (or I probably wouldn't have to ask)... Does the software have a setting for type of petrol injection (sequential / semi sequential / full group)? If so it would be better to select sequential but then you'll have to do a full re-calibration. I know that the old AG/Teleflex systems all ran group injection even on sequential engines, there are a confusing range of ECUs with AG in the brandname but I don't know if AGIS is a more recent development from the makers of the old AG / Teleflex system (in which case you might not be able to select sequential, in which case the system will most likely have to run group injection but not necessarily so - it may run sequential even though figures on screen reflect group injection readings). Does the rpm reading on screen agree with the car's rev counter?
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Re: Mercedes C class w204

#9 Post by i860 » Sun Dec 16, 2018 5:50 pm

Hi
LTFT use to change slowly, but after I update the car ecu the ltft is changing very fast like the stft, have you seen this on any cars?
You can play with the program just select demo mode after you install and lunch the program.

AGIS M210_P13 ver 1.51 installer
https://www.acon.com.pl/pl/produkty/13- ... 8-agis-p12

W204 is selected as full sequential on the lpg ecu ( the photo is from demo mode not connected to the car, in there i have ....)

Yes the rpm from the program is the same like on the spedo.
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Re: Mercedes C class w204

#10 Post by LPGC » Sun Dec 16, 2018 9:02 pm

i860 wrote:
Sun Dec 16, 2018 5:50 pm
Hi
LTFT use to change slowly, but after I update the car ecu the ltft is changing very fast like the stft, have you seen this on any cars?
You can play with the program just select demo mode after you install and lunch the program.

AGIS M210_P13 ver 1.51 installer
https://www.acon.com.pl/pl/produkty/13- ... 8-agis-p12

W204 is selected as full sequential on the lpg ecu ( the photo is from demo mode not connected to the car, in there i have ....)

Yes the rpm from the program is the same like on the spedo.
Yes I regularly see ltft's seeming to update / change at varying speed. Sometimes this is what's really happening, sometimes it isn't really happening but seems to be happening due to the speed of the interface between the OBD scan tool (or LPG system OBD connection). When it really happens it can be due to the petrol ECU being in some sort of limp mode or not having passed it's IM readiness self checks or not having met some condition such as engine not fully warmed up. If you have changed the ECU it is possible that the (different spec?) ECU runs a different set of ltft ranges anyway. E.g. relatively old spec engine ECUs might only have had one ltft that covered the entire rpm and load range, more modern ECUs seem to have more and more ltft ranges.
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Re: Mercedes C class w204

#11 Post by i860 » Mon Dec 17, 2018 9:28 am

So if the LTFT is -1.6% on bank1 and -0.8% bank2 over 8k miles that means that the tunning on lpg is really good?
On petrol in an ideal world will be 0% ltft both banks.

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Re: Mercedes C class w204

#12 Post by LPGC » Mon Dec 17, 2018 10:29 am

In your video don't the ltft's reach 7%?
It also depends on what you call good tuning... Are you aiming for zero trims, same trims as petrol or somewhere in-between? There can be advantages to each depending on a few factors such as model of vehicle, what the readings are and to some extent knowing why trims (on petrol) are what they are. In most cases somewhere in-between makes most sense.
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Re: Mercedes C class w204

#13 Post by i860 » Mon Dec 17, 2018 11:56 am

Yes the LTFT reaches 7% during driving, if I switch off the engine and put the key in the ignition I can read the LTFT properly.
So if with the engine running LTFT is all over the place with the engine off I can get the exact value.
Before converting to LPG the LTFT is was 3.1% on both banks, I am trying to bringing the ltft to 0% or negative value no more than -4.5% both banks is that ok?

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Re: Mercedes C class w204

#14 Post by LPGC » Mon Dec 17, 2018 12:54 pm

No..
Like I've said a few times, there are many ltft's and the engine needs to be driven over a wide range of conditions to check them all.
Reading ltft without the engine running is almost pointless.
If you read an ltft of e.g. +5% and while reading that +5% ltft the stft is almost constantly at +5%, what will happen over time is that the +5% ltft will become +10% and the stft will come close to 0% - because the stft's steer ltfts over time. The fuelling the engine gets is the ECU's base map +ltft +stft. Stft's are a momentary correction to fuelling but over time they steer ltft's. Ltft's are stored in the ECU so that when you next at first drive the engine at a point in the ECU's map which is within the range of rpm and engine load that the ltft covers the fuelling will be more correct with zero stft.
Another way of putting it - Actual fuelling is base map + ltft +stft, if you have ltft of +5% and stft of +5% this equates to base map +10%, and if you have ltft of +10% and stft of 0% it still equates to fuelling of base map +10%. This is how the petrol ECU learns to provide more correct mixture to your engine sooner with changing engine rpm/load combinations as you drive (because momentary stft's affect ECU stored ltft's over time). So, if you have ltft of +10% on petrol and you calibrate the LPG system to steer ltft's to 0% the mixture will be correct less of the time, especially when you switch between different fuels, because the ltft's will need to be relearned every time you switch between fuels - until they are all relearned whenever you change the engine rpm or load enough to cause
the petrol ECU to switch to another ltft range the engine will at first get slightly incorrect fuelling until the stft steers the mixture to correct, but if you had calibrated the LPG system so that ltft's on LPG could stay the same as ltft's when running on petrol the mixture would be correct more of the time because the ECU wouldn't have to relearn ltft's every time you switched fuels.
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