RPM sensor on MegaSquirt II Extra question

[ShadowofBob]

So I built up a V3.0 board to run MS2Extra on my Audi Coupe for when the time comes to turbocharge it. I further added a challenge by using only OEM sensors where ever possible and building the MS board into my Audi ECU box.

I tried to get it running the other day, but ran into some issues. The stock 5 cyl 20v Audi motors used 3 sensors to figure out timing: 2 VRs and 1 Hall. The 2 VR get signals from the flywheel. One counts the physical teeth that the starter gear cranks on to give the engine an RPM signal. The second one sees a pin at TDC and is only used on initial start up. The hall sensor is used to tell where the cam is. I can't use just the hall sensor because it is a single window and doesn't have enough detail.

I decided to try to use the dual trigger setup in MS2Extra. Using the VR sesnor that counts the teeth and the hall to get the cam position. I counted the teeth on the flywheel to be 134. Unfortunately if I put in a value higher than 120 teeth into the trigger wheel settings MS goes crazy and none of my IAT, coolant temps, etc read accurately and RPMs are pegged at 63,000ish with the motor not moving. Is there some limitation regarding max teeth or multiples of numbers I can use for the VR sensor?

Has anyone else here gotten their car to run using the factory timing sensors?

[S2central.net]

I thought you had to go with a 60-2 arrangement on VEMS / Megasquirt. Not the expert on that - just a recollection.

As to the factory sensors you speak of, let me clarify a few things.

There are indeed two 'VR' types on the flywheel. One provides crankshaft position sensing (CPS) with an inductive pulse at 62 degrees BTDC on #1. This signal is ALWAYS needed by the ECU. More on that later.

The 2nd VR is the RPM sensor... There are actually 135 teeth and you need to do some basic math to understand how the pulse timings correlate to rpm on the 5-cyl.

The hall sensor provides a pulse to determine when the camshaft is approaching TDC on #1. THis is how the ECU determine where #1 is... The hall signal is such that the CPS pulse will be inside that window every other crank revolution (4-strokes if you like).

The hall sensor is needed at startup by the factory ECU but once learnt it can adapt to it being missing if disconnected after the engine starts.

I have another thread on here with that simple math and some waveforms you can look at.

[S2central.net]

Voila ----

http://www.s2forum.com/forum/showthread.php?t=30947

[ShadowofBob]

Thanks for that info, really helpful. Must have been off a tooth while counting. I'll have to see if MSIIExtra will take 135 tooth or still go crazy. I guess either everyone on Audiworld is misinformed about the crank position sensor or the hitachi EMS handles it differently than motronic.

[S2central.net]

Its easy to test on a Motronic system with engine running...

Disconnect hall sensor and it still runs - but ignition is retarded for safety.... Stop the engine and it wont start until hall sensor plugged in again.

Disconnect CPS or RPM sensor and it dies.

[ifa]

If G4 signal is missing on running engine it goes to safe mode.

[S2central.net]

G40 actually - but yes

[ifa]

AAN and ABY engines G4 and G40 can be unplugged on running engine. It just goes to safe mode.
All three must work to start the engine.

If G28 loses on running engine it dies.

[Biggy]

Thanks for that info, really helpful. Must have been off a tooth while counting. I'll have to see if MSIIExtra will take 135 tooth or still go crazy. I guess either everyone on Audiworld is misinformed about the crank position sensor or the hitachi EMS handles it differently than motronic.

Ideally you should have a flywheel with M teeth and N teeth missing. Where M>N, M can be divided by number of cylinders and 360 can be divided by M. But in fact MS works correctly with 120 or less teeth flywheel only.

So in our (I5t) case, you need to make an extension board for your MS ECU, a "divider" (135 divide by 3), to convert 135+1 (teeth) signal from your original flywheel VR sensors, to virtual 45-1 that MegaSquirt will understand correctly.
360 can be divided by 45, 45 can be divided by 5 cylinders, and 45>1.

Thats what i did on my UrS4.

Otherwise you can make a 60-2 sprocket and weld it to the crankshaft pulley, as it is made in stock on Lancias for example, and use one original VR sensor.

034 offers what you need http://www.034motorsport.com/index.php?cPath=22_30_27

[UrS4boy]

I guess either everyone on Audiworld is misinformed about the crank position sensor or the hitachi EMS handles it differently than motronic.

Gee, now why would it be surprising that a Hitachi EMS for a normally aspirated7A might be different than a Bosch Motronic ECU for a turbo-charged AAN, ABY or ADU?

Basic information about the sensors that the Motronic ECU needs to work with, including the G40 Cam Position Sender, the G4 Crank Position Sensor and the G28 Engine speed sensor is found here:

AAN Engine Bay Device Map (pull down for the hyperlinks)

In addition, and perhaps more importantly, Marc Swanson (a4quattro on AudiWorld) in the US has developed a plug and play VEMS kit that uses ALL of the 3B or AAN (presumably ABY and ADU) sensors (hall, crank position, engine speed, etc). The link to Marc's website is at:

http://www.efiexpress.com/catalog/pr...?products_id=1

HTH

[ShadowofBob]

I ended up buying a wheel translator board that takes the 135 tooth wheel divides by 3 and combines the single pin VR sensor at TDC effectively creating a virtual 45-1 tooth wheel. Unfortunately I can't get a signal to megasquirt yet. It still sees no RPM signal. I really need a handheld oscilloscope to diagnose whether it is hardware or software.

http://jbperf.com/wheel_translator/index.html

Gee, now why would it be surprising that a Hitachi EMS for a normally aspirated7A might be different than a Bosch Motronic ECU for a turbo-charged AAN, ABY or ADU?

Despite the fact that they are different they still share nearly all of the same sensors short of the MAF, IAC valve, and maybe the TPS setup.

[UrS4boy]

Despite the fact that they are different they still share nearly all of the same sensors short of the MAF, IAC valve, and maybe the TPS setup.

So, in the end, they are different.

That car is exactly like mine except for the colour, wheels, number of doors and the make. Other than that, they are identical.

On a serious note, you should contact Marc S. (a4quattro here)

[gedu]

I'll just chime in that VEMS can use original Audi trigger mechanism

[Biggy]

I ended up buying a wheel translator board that takes the 135 tooth wheel divides by 3 and combines the single pin VR sensor at TDC effectively creating a virtual 45-1 tooth wheel. Unfortunately I can't get a signal to megasquirt yet. It still sees no RPM signal. I really need a handheld oscilloscope to diagnose whether it is hardware or software.

The problem may be in decoding. The "-1" tooth signal should correspond to the hall sensor signal.

I had such problem. The translator was mistakening 1 tooth in corresponding to hall signal. No rpm, no starting. As soon as everything is diveded by 3 - the mistake was equal to 3 teeth in real. The problem was solved by reprogramming the chip on the divider(translator) board.

[Biggy]

I ended up buying a wheel translator board that takes the 135 tooth wheel divides by 3 and combines the single pin VR sensor at TDC effectively creating a virtual 45-1 tooth wheel. Unfortunately I can't get a signal to megasquirt yet. It still sees no RPM signal. I really need a handheld oscilloscope to diagnose whether it is hardware or software.

http://jbperf.com/wheel_translator/index.html


Despite the fact that they are different they still share nearly all of the same sensors short of the MAF, IAC valve, and maybe the TPS setup.

I'll just chime in that VEMS can use original Audi trigger mechanism

it already has a built-in wheel translator.

Megasquirt is like I-Phone. It can do almost everything you want, but you have to build it yourself, step-by step.