Flex Fuel reading 4v problem

jmctuning

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Aug 8, 2018
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jmctuning.com
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e92 335i N54
Hello to anyone who can assist me with my Flex Fuel issue

I have setup flex fuel using a specific MHD tune from an experienced tuner (JSR) and a fuel-IT ethanol analyzer which can read over bluetooth plus on a 0-5v signal wire

My setup; The ECA analyzer wire plugged into Harness PIN#16 on the black 26 pin sub
Capture2.JPG

Issue I'm having is #pin16 has 4v coming out of it which is normal based on my testing this car and others. However when I plug my ECA signal wire which currently has 0.28v (pump gas) it doesn't change the PIN16 voltage to the ECA reading but rather keeps the 4v resulting in a E reading of E80 on MHD and my JB4
Capture3.JPG

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My fuel-IT app shows E4 which is correct based on pump gas and 0.28v which I measured with a multimeter

My tuner has double checked the tune and seeing as I can see E content in both MHD and JB4 it looks right. But because I have a persistent 4v on PIN16 my E content is skewed

Important to note;
I installed a new DME MSD81 which came from a 135 from 2008 from the USA. I have my old mds80 but is now not coded to my CAS

I have a theory which comes from looking at the wiring diagrams attached in the PDF at the end of my thread

In the USA PIN 16 and PIN17 were used for these functions

16 E USA Signal, fuel tank leak diagnosis pump Diagnostic module for fuel tank leakage
17 E USA Signal, fuel tank leak diagnosis heating Diagnostic module for fuel tank leakage

Could I have a coding issue on this DME which means a conflict between function ????

I did also try plugging in the ECA signal only into the JB4 PIN2 on the DB25 plug and E shows up correct. the analyzer is working as intended

All I can think is at fault is the DME coding is somehow causing the issue
 

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CantSitStill

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Jul 22, 2022
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Just did a few tests. With the hsf4 unplugged (reading at that plug) I get 4v, same as MHD. With it plugged in, measured at the same plug I get 3v.

If I measure the voltage outputted by the controller witu the plug for the dme out it gives me 0.5v as it should
 

[email protected]

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Philly
That is weird. I would reach out to aquamist and see what they say. Are you flashing a proper bin via MHD? Is it converting the voltage to a %? (Logged as ethanol content (wired)) in the latest app
 

CantSitStill

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Jul 22, 2022
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It's using the v1 flex tune from wedge. The conversion works OK I believe as I'm getting the correct % for ethanol content wired. Mhd shows you the voltage regardless of flex enabled or not as far as I can tell. You need the flex tune to get it to show the ethanol content. Reached out to Richard. If I test with a battery can I just put the neg to the car body and pos to the dme input (pin 16)
 

CantSitStill

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Jul 22, 2022
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It's using the v1 flex tune from wedge. The conversion works OK I believe as I'm getting the correct % for ethanol content wired. Mhd shows you the voltage regardless of flex enabled or not as far as I can tell. You need the flex tune to get it to show the ethanol content. Reached out to Richard. If I test with a battery can I just put the neg to the car body and pos to the dme input (pin 16)
Tested with the battery and gives me 1.7v perfect (a new duracell). I tested the earth to the hfs4 controller and works perfectly. Maybe the controller then...going to test it some more to see what else is not working if anything as this is the first time I have powered it on
 

CantSitStill

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Jul 22, 2022
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Just for my curiosity. If the dme defaults to 4v does this mean that on a cable issue (cable gets disconnected) the dme will see ethanol flow when there is not?
 

CantSitStill

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Jul 22, 2022
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Spoke to Aquamist and he believes the pull up resistor on the dme that creates the 0-5v signal is bigger than expected and the hfs4 does not have enough current to overcome it. He is going to give me a solution to increase the power output of the hfs4. Stay tuned!
 

CantSitStill

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Jul 22, 2022
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Sorted. I had to remove a resistor and bridge it with solder as the current output was limited to a few ma and this is not enough to overcome the DME.

IMG-20220723-WA0004.jpg
 
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CantSitStill

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Jul 22, 2022
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@[email protected]

Richard is asking if there is any way its possible to disable the DME pull up resistor in the tune so the default 4v is not applied when the cable is disconnected to pin 16 on the dme.

As it is when the cable gets disconnected it defaults to 4v which is being seen as 100% flow so it just an extra failsafe. Ideally it should read 0v (0% flow) if it gets disconnected
 

[email protected]

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Yes it would require a change in the port/pad config in DME init, but that type of stuff can take weeks to trace and identify, not something I have time to do.

He can create a firmware for use here that outputs say 0.5V to 3V for 0-100% flow, then you can setup the voltage conversion table 3rd cell to be the "safety" cell and have it use 4V+ as 0%. That is why the Motiv FF kit uses the smaller voltage range.
 

CantSitStill

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Jul 22, 2022
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Yes it would require a change in the port/pad config in DME init, but that type of stuff can take weeks to trace and identify, not something I have time to do.

He can create a firmware for use here that outputs say 0.5V to 3V for 0-100% flow, then you can setup the voltage conversion table 3rd cell to be the "safety" cell and have it use 4V+ as 0%. That is why the Motiv FF kit uses the smaller voltage range.
Thanks. I messed about with a jb4 bin and found that works pretty well. 0.75v no flow, 4v max flow, 4.01v no flow (safety)
 
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CantSitStill

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Jul 22, 2022
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Hello. Now that i have the ECA voltage working well i have another problem. Im having weird starting issues where it wont start or the HPFP is taking ages to build up (i can see that happening). Now if i flash back to a non flex fuel map it works perfectly - starts instantly hot or cold. But with the flex fuel map applied it will either take about 5-10 secs of cranking and gradually starting once it reaches 2500 psi or like this morning it wont start at all (fuel pressure was OK this time but would not fire). Each time it's fixed by flashing back to non flex map.

What is even stranger is that last night i selected a ECA option in MHD (Motiv) and it worked for a period and i thought that was what i was doing wrong - not selecting the option (i thought that was all included in the custom flash). Anyway this morning the only difference was that it was a bit cooler and it would not fire up at all. Reset all the adaptions in desperation, still nothing, flashed back to non flex and started perfectly.

@[email protected] do you know if there is any special logic in those ECA options that might cause my problems? (as in I'm selecting an option for kit i dont have installed). It seems to be caused or triggered by the flex fuel map or those options. Obviously there is not an option for the auqamist but i assumed i would not need one and just be able to select one as long a Ken is adjusting the voltage options on the custom side.

The most consistent issue just now im seeing is the slow build up of the high pressure fuel on the flex fuel map - any thoughts?

EDIT - Should mention I get no codes when the issue is happening and is more obvious when it's warm.

EDIT: I did some more testing. I started the car in stages as it cooled down. At about 140f (coolant) it starts normally again so when it worked last night I must not have got over the 140f coolant threshold so it seemed OK. Anything over that it progressively takes longer where at about 190f it takes the longest. As for the issue with it not starting from 50f (in the morning) yet to test that again, could have been something else as it actually had fuel pressure OK that time.

Are there any warm start tables that can get screwed up?
 
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