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vwnut8392
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« on: May 11, 2023, 12:27:56 PM »
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im in the middle of swapping a 1.8T from B6 A4 into a 1984 4000 and was thinking about the tach functionality. looks like the only way to currently make the original tach work is with some sort of converter which im not really into. this lead me to an idea wondering if there was a spare output pin that could used to drive an analog tach? if i remember correctly all the old 80's clusters need to see 4 pulse per revolution of the engine for 4 cylinder where as if i where to tap into just the cylinder 1 coil or injector that is not enough to drive it properly. its a sort of waste spark vs sequential spark problem. so the idea is to figure out in code where the final ignition events happen, somehow copy them into an open spot in RAM than have code elsewhere running that when it sees a trigger event in RAM it opens the spare output to trigger the tach. this is just an idea but i think it would be possible to do it this way with a code patch to avoid having to use external devices to drive an older VAG tach.
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mdz
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« Reply #1 on: May 11, 2023, 02:32:15 PM »
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If problem is CAN vs analog tach signal, then B6 ecu outputs analog rpm signal without any custom code.  |
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ratosluaf
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« Reply #2 on: May 11, 2023, 09:57:26 PM »
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analog rpm is on pin 37, often stated as something related to A/C in pinouts
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vwnut8392
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« Reply #3 on: May 15, 2023, 03:06:57 PM »
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interesting, did not know this. im using 06A 906 032HS ECU from a GTI in this car, the donor cars ECU was already missing.
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vwnut8392
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« Reply #4 on: May 28, 2023, 07:30:29 PM »
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tried pin 37 and it does not work with my tach in my swap. so back to this and adding custom code for it. i think the problem is my tach in my 82 4000 requires 4 pulses per revolution and the ME7.5 ECU is only outputting 1 pulse per revolution. im wondering if in the code its as easy as multiply the output by 4 and it just works? not really sure where or how to start hunting for the code for that output though. function sheet section about the outputs is blank.
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ratosluaf
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« Reply #5 on: May 28, 2023, 09:50:13 PM »
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whats your ecu p/n?, mine was 4b0906018dh and rpm pin was on pin 37, outputting 4 pulses per revolution.
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vwnut8392
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« Reply #6 on: May 28, 2023, 11:15:21 PM »
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whats your ecu p/n?, mine was 4b0906018dh and rpm pin was on pin 37, outputting 4 pulses per revolution.
06A 906 032 HS from a 2002 VW GTI. |
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vwnut8392
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« Reply #7 on: May 28, 2023, 11:33:17 PM »
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I found ME7.5 schematics that gives me my first clue how to find its code in disassembly. First picture shows the output pin from the processor highlighted in green. it outputs on pin 2.13. Second picture shows pin 2.13 outputting through its circuit to the ECU connector. i found references like this in several places in my disassembly where its setting or clearing P2_13 or setting P2_13 but im not sure if its actually doing somthing with that port or if its just a coincidence. [code] bset P2_13 ; Bit Set [/code] |
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« Last Edit: May 29, 2023, 12:27:08 AM by vwnut8392 »
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prj
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« Reply #8 on: May 29, 2023, 12:08:09 AM »
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There's a high/low change every 30 teeth of the trigger wheel.
So if the tach can read it, then it should show RPM. Whether the correct one or not is a different question.
If it shows nothing you have the wrong pin or the wrong signal level, in which case no amount of software will help you.
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terok
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« Reply #10 on: May 29, 2023, 09:29:16 AM »
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Highly likely that tacho has input circuitry which needs high voltage spikes from coil negative. It might not work with 12v square wave. This is the case in older VW tachos. You can easily bypass this circuit and then tacho is happily showing correct rpm.
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vwnut8392
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« Reply #11 on: May 29, 2023, 10:07:47 AM »
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Highly likely that tacho has input circuitry which needs high voltage spikes from coil negative. It might not work with 12v square wave. This is the case in older VW tachos. You can easily bypass this circuit and then tacho is happily showing correct rpm.
looking at the original wiring for the tach in the car it does appear that it is exactly that because it gets its signal directly off of the negative side of the coil. i had to actually separate the circuit under the dash because it also used to trigger the fuel pump relay on. the ME7 now controls the original fuel pump relay. i did continuity tests between ECU pin 37 and the connector at the back of the cluster with the red/black/yellow wire and im definitely connected with the connector for the gauge. when you say bypass the circuit do you mean bypass it in the ECU or bypass it on the circuitry in the tach itself? one thing i did try was to see if i could even see pulses with a noid light which i do not. the noid light just shows ground the whole time the engine is running. very little info out there about this output specifically. what exactly is its output? is it 5V square wave? |
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vwnut8392
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« Reply #12 on: May 29, 2023, 10:59:39 AM »
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There's a high/low change every 30 teeth of the trigger wheel.
So if the tach can read it, then it should show RPM. Whether the correct one or not is a different question.
If it shows nothing you have the wrong pin or the wrong signal level, in which case no amount of software will help you.
so if there is a high/low change every 30 teeth that would make it output 2 pulses per one full revolution being that it has a 60-2 trigger wheel on the crank. the original setup in my case was 4 pulses per revolution. with that known my tach would require the change every 15 teeth of the crank sensor instead of 30 to get the 4 pulses. |
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« Last Edit: May 29, 2023, 11:02:06 AM by vwnut8392 »
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vwnut8392
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« Reply #13 on: May 29, 2023, 11:28:00 AM »
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yes, i seen that and it only establishes that ECU pin 37 can output a tach signal. no specifics on what sort of signal it actually outputs. |
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BlackT
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« Reply #14 on: May 29, 2023, 11:37:47 AM »
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I once have swap 2.0 ABK to audi B2, tacho was working and it was connected to ECU
ABK ecu have same output for tacho as any other 4 zylinder ECU for audi/VW inclunding ME7.5
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