O.E trigger for rev counter
Discussion
Does anybody know how a standard rev counter via the standard ECU uses the flywheel to provide RPM?
What I'm wondering is if it simply looks for the missing tooth in the flywheel to measure rpm. Or does it count the other teeth in any way?
I have a 206 GTI running an Omex 600 ECU from the standard crank sensor reading the timing marks on the flywheel.
Sharing the crank sensor is the wiring to the original rev counter. I want to separate the 2 wiring systems and maybe run the rev counter from a new trigger wheel and sensor on the crank pulley with a missing tooth. Does anybody know if this solution might work? I.e. is one missing tooth all that's needed for the ECU to count the rpm?
I can't use the Omex rpm output as the standard rev counter gets a signal from the original ECU and I have no idea what signal it would need to work.
What I'm wondering is if it simply looks for the missing tooth in the flywheel to measure rpm. Or does it count the other teeth in any way?
I have a 206 GTI running an Omex 600 ECU from the standard crank sensor reading the timing marks on the flywheel.
Sharing the crank sensor is the wiring to the original rev counter. I want to separate the 2 wiring systems and maybe run the rev counter from a new trigger wheel and sensor on the crank pulley with a missing tooth. Does anybody know if this solution might work? I.e. is one missing tooth all that's needed for the ECU to count the rpm?
I can't use the Omex rpm output as the standard rev counter gets a signal from the original ECU and I have no idea what signal it would need to work.
Sensibleboy said:
Sharing the crank sensor is the wiring to the original rev counter.
...
the standard rev counter gets a signal from the original ECU
Where did the rev counter take its signal from originally? It is unclear from your post whether it was originally connected to the crank position sensor (which seems unlikely) or took its signal from the ECU....
the standard rev counter gets a signal from the original ECU
Sensibleboy said:
The rev counter originally took its signal from the ECU
It seems unlikely that the ECU output the same analog signal it got from the sensor and more likely it is a completely different digital signal. If you can find out what type of signal it needs I expect there'll be a way to generate it - finding out what signal it needs strikes me as the hardest part of this problem.Page 25 mentions that the OMEX 600 tachometer output can directly drive any tachometer that is normally controlled by an ECU
http://omextechnology.co.uk/600%20ECU%20Installati...
http://omextechnology.co.uk/600%20ECU%20Installati...
Sensibleboy said:
Does anybody know how a standard rev counter via the standard ECU uses the flywheel to provide RPM?
What I'm wondering is if it simply looks for the missing tooth in the flywheel to measure rpm. Or does it count the other teeth in any way?
I have a 206 GTI running an Omex 600 ECU from the standard crank sensor reading the timing marks on the flywheel.
Sharing the crank sensor is the wiring to the original rev counter. I want to separate the 2 wiring systems and maybe run the rev counter from a new trigger wheel and sensor on the crank pulley with a missing tooth. Does anybody know if this solution might work? I.e. is one missing tooth all that's needed for the ECU to count the rpm?
I can't use the Omex rpm output as the standard rev counter gets a signal from the original ECU and I have no idea what signal it would need to work.
So the rev counter got it's signal from the ecu...and you have another ecu which offers a signal for a rev counter and you seem to think that wont work ?What I'm wondering is if it simply looks for the missing tooth in the flywheel to measure rpm. Or does it count the other teeth in any way?
I have a 206 GTI running an Omex 600 ECU from the standard crank sensor reading the timing marks on the flywheel.
Sharing the crank sensor is the wiring to the original rev counter. I want to separate the 2 wiring systems and maybe run the rev counter from a new trigger wheel and sensor on the crank pulley with a missing tooth. Does anybody know if this solution might work? I.e. is one missing tooth all that's needed for the ECU to count the rpm?
I can't use the Omex rpm output as the standard rev counter gets a signal from the original ECU and I have no idea what signal it would need to work.
Think about that for a second....
stevieturbo said:
So the rev counter got it's signal from the ecu...and you have another ecu which offers a signal for a rev counter and you seem to think that wont work ?
Think about that for a second....
I looked for the information due to not understanding what was so complicated and why be thinking about a 2nd sensor/plateThink about that for a second....
Interesting comment about the Omex instructions. It doesn't state how it's done though. I will ask them tomorrow.
The company that did the Omex and throttle body fitting seem to have done some experimentation with the Omex tacho output but decided to not use it. I'm wondering if this was for good reason- I.e. they couldn't get it to work.
I don't think I put my original question across very clearly.
I'm thinking about replicating the original flywheel trigger setup on the crank pulley just to work the rev counter. So it will have an aftermarket trigger wheel attached with just one wide notch in it to replicate the missing tooth. No other timing marks will be on the trigger wheel.
I'm trying to work out if this simple wheel with one notch in it is likely to work with the original ECU to work the rev counter.
This will allow me to run the two electrical system completely independent from each other.
The company that did the Omex and throttle body fitting seem to have done some experimentation with the Omex tacho output but decided to not use it. I'm wondering if this was for good reason- I.e. they couldn't get it to work.
I don't think I put my original question across very clearly.
I'm thinking about replicating the original flywheel trigger setup on the crank pulley just to work the rev counter. So it will have an aftermarket trigger wheel attached with just one wide notch in it to replicate the missing tooth. No other timing marks will be on the trigger wheel.
I'm trying to work out if this simple wheel with one notch in it is likely to work with the original ECU to work the rev counter.
This will allow me to run the two electrical system completely independent from each other.
Edited by Sensibleboy on Sunday 12th November 19:03
Edited by Sensibleboy on Sunday 12th November 19:03
Sensibleboy said:
Interesting comment about the Omex instructions. It doesn't state how it's done though. I will ask them tomorrow.
The company that did the Omex and throttle body fitting seem to have done some experimentation with the Omex tacho output but decided to not use it. I'm wondering if this was for good reason- I.e. they couldn't get it to work.
I don't think I put my original question across very clearly.
I'm thinking about replicating the original flywheel trigger setup on the crank pulley just to work the rev counter. So it will have an aftermarket trigger wheel attached with just one wide notch in it to replicate the missing tooth. No other timing marks will be on the trigger wheel.
I'm trying to work out if this simple wheel with one notch in it is likely to work with the original ECU to work the rev counter.
This will allow me to run the two electrical system completely independent from each other.
I was going to suggest something earlier and thought to myself "the OP wont want to have another ECU on the car for running a Tacho and nothing else"The company that did the Omex and throttle body fitting seem to have done some experimentation with the Omex tacho output but decided to not use it. I'm wondering if this was for good reason- I.e. they couldn't get it to work.
I don't think I put my original question across very clearly.
I'm thinking about replicating the original flywheel trigger setup on the crank pulley just to work the rev counter. So it will have an aftermarket trigger wheel attached with just one wide notch in it to replicate the missing tooth. No other timing marks will be on the trigger wheel.
I'm trying to work out if this simple wheel with one notch in it is likely to work with the original ECU to work the rev counter.
This will allow me to run the two electrical system completely independent from each other.
Edited by Sensibleboy on Sunday 12th November 19:03
Edited by Sensibleboy on Sunday 12th November 19:03
If you are ok for wiring the original ECU for running the Tacho - There is nothing stopping you from making a bracket and fitting the original crank sensor in a different position above or below the OMEX circuits sensor. The Tacho will work no matter what the sensor position is, the Tacho does not rely on position, I stand to be corrected but am pretty confident this will work
The problem I have is I don't know your engine, I don't know if there is room for a second sensor
Edited by Penelope Stoppedit on Sunday 12th November 19:17
The ecu on a 205 is iirc, an analogue bosch one? Ie, no microprocessor, just some gain curves hard coded by different resistor values into some opamps in the ecu. Pretty sure it's a batch fire system as well (ie all injectors fire at once, once per rev)
I suspect the crank sensor output therefore is a simple analogue filtered version of the raw crank sensor signal, which will be a bipolar signal as it's from a Variable Reluctance type sensor. Most analogue rev counters have a very basic signal processing front end, and the only thing that is likely to make a difference is if the trigger edge has to go below ground or not, ie, is the edge decoding done on a signal that cross up though 0v from a negative voltage (zero volts threshold) or done on signal that rised up from 0v to some other higher positive voltage (often 0-5v or 0-12v) and the threshold point is somewhere in the middle of that range
I suspect a bit of googling might uncover a bit more info, or take a look at the rev counter itself to see what it's front end looks like circuit wise.
I suspect the crank sensor output therefore is a simple analogue filtered version of the raw crank sensor signal, which will be a bipolar signal as it's from a Variable Reluctance type sensor. Most analogue rev counters have a very basic signal processing front end, and the only thing that is likely to make a difference is if the trigger edge has to go below ground or not, ie, is the edge decoding done on a signal that cross up though 0v from a negative voltage (zero volts threshold) or done on signal that rised up from 0v to some other higher positive voltage (often 0-5v or 0-12v) and the threshold point is somewhere in the middle of that range
I suspect a bit of googling might uncover a bit more info, or take a look at the rev counter itself to see what it's front end looks like circuit wise.
I need to keep the original ECU because other stuff like road speed and temperature go through it.
The car even has two coolant sensors, one for the omex and one for the temp gauge.
I have looked at fitted another crank sensor on the gearbox housing to run from the flywheel but there is no suitable place.
The car even has two coolant sensors, one for the omex and one for the temp gauge.
I have looked at fitted another crank sensor on the gearbox housing to run from the flywheel but there is no suitable place.
er, scratch all that, i just noticed you wrote 206, not 205!! DOH!
Ok, that's almost certianly using a uni-polar 0-5v square wave output put from the original ecu, so the omex tacho drive should have no problems driving the tacho directly. All you'll have to do is work out the gauges pulses per rpm calibration, which you can do with a timing light on the engine for reference
Ok, that's almost certianly using a uni-polar 0-5v square wave output put from the original ecu, so the omex tacho drive should have no problems driving the tacho directly. All you'll have to do is work out the gauges pulses per rpm calibration, which you can do with a timing light on the engine for reference
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