Wiring up Rev Counter

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downside190
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Wiring up Rev Counter

Post by downside190 »

Can anyone give me advice on how to wire up my rev counter?

I want to use the standard rev counter in my mercedes 190e, the tach signal wire currently connects to the VR sensor, engine is using a COP Wasted spark setup. Do I just wire the tach signal to my rev counter as well or is there more too it?

I've tried searchiing but not found much info on the v2.2 version of megasquirt that i'm.
PSIG
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Re: Wiring up Rev Counter

Post by PSIG »

downside190 wrote:... the tach signal wire currently connects to the VR sensor ...
Is that how it connects in stock form? If so, it should work fine using the factory hookup, if you are also using the factory VR sensor and trigger wheel.

David
-=≡ If it was easy, everyone would do it. ≡=-
downside190
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Re: Wiring up Rev Counter

Post by downside190 »

PSIG wrote:
downside190 wrote:... the tach signal wire currently connects to the VR sensor ...
Is that how it connects in stock form? If so, it should work fine using the factory hookup, if you are also using the factory VR sensor and trigger wheel.

David
I've added the trigger wheel and VR sensor as the original engine got its reading from the crank sensor on the gearbox but I couldn't get that working so ditched it. Thats why i'm at a bit of a loss as to how I now wire it up?

Edit: Just to add, the I wired up a jean duel vr board for the vr sensor signals.
PSIG
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Re: Wiring up Rev Counter

Post by PSIG »

downside190 wrote:... the original engine got its reading from the crank sensor on the gearbox but I couldn't get that working ...
I don't know what the factory tach originally received for a signal (pulses-per-rev) and whether is was directly from the sensor or processed through the ECM, so I can't help with duplicating that unknown signal. I simply do not have enough information.
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David
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john.p.clegg
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Re: Wiring up Rev Counter

Post by john.p.clegg »

downside190
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Re: Wiring up Rev Counter

Post by downside190 »

PSIG wrote:
downside190 wrote:... the original engine got its reading from the crank sensor on the gearbox but I couldn't get that working ...
I don't know what the factory tach originally received for a signal (pulses-per-rev) and whether is was directly from the sensor or processed through the ECM, so I can't help with duplicating that unknown signal. I simply do not have enough information.
Image
David
I still have the factory ecu in place and from the wiring diagrams its looks like its just one wire that goes from the gauge to the ecu to the tacho signal wire.

I'm just not sure if I build the circuit that john.p.clegg posted and join it to the signal wire if that will work or if it will cause problems with the vr sensor. Guess I can always try it and see what happens.
PSIG
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Re: Wiring up Rev Counter

Post by PSIG »

If the original tach signal came through the ECM, then it will be a low-voltage signal. However, that is not the problem. The problem is knowing what signal information the tach needs to see. It's like yelling at someone (they can hear you), but in a foreign language, so they do not know what to do. You need to research what signal the factory tach needs (4 pulses-per-rev? 168 pulses-per-rev?). Then it will be much easier to figure out a way to feed it that correct signal information. See what I mean?

David
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downside190
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Re: Wiring up Rev Counter

Post by downside190 »

PSIG wrote:If the original tach signal came through the ECM, then it will be a low-voltage signal. However, that is not the problem. The problem is knowing what signal information the tach needs to see. It's like yelling at someone (they can hear you), but in a foreign language, so they do not know what to do. You need to research what signal the factory tach needs (4 pulses-per-rev? 168 pulses-per-rev?). Then it will be much easier to figure out a way to feed it that correct signal information. See what I mean?

David

Hi

Just coming back to this, how do I find out what singal the original factory tach needs? Is there way to test for this?
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