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Discussion Starter #1
hi everyone.
I've got a question for you.
How do I get the rpm signal into the electronic AEM gauge?
I want to set the alarms on this gauge but I need the the engine rpm
signal.
Without the rpms it can't be done well...
My mechanic is suggesting to take the signal from the ignition coil
what do you think about it?
Hope you can help.
Regards
 

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I agree with your mechanic. That's where Dyno technicians get the RPM signal as well.
 
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Discussion Starter #3
Thanks Ruben,
I'll start working on it on Monday. The only thing that worries my mechanic is that the car has 8 coils. I was connecting the gauges this way but the car had 6 cylinders and 1 coil. I wonder how the aem gauge will react.
On Monday I'll be also installing the oil cooler. As soon as I get this over with I'll show some new images of it.
Thanks


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Thanks Ruben,
I'll start working on it on Monday. The only thing that worries my mechanic is that the car has 8 coils. I was connecting the gauges this way but the car had 6 cylinders and 1 coil. I wonder how the aem gauge will react.
On Monday I'll be also installing the oil cooler. As soon as I get this over with I'll show some new images of it.
Thanks


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All coils should be reporting the same RPM. You can do what Peter mentioned above as an option or tap the main computer (this is where the coils signal comes to) pin 18 or 33 cant remember, but its a brown/white or just brown wire.
 
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What kind of signal does the manual say the gauge is looking for?

There is no such thing as a "simple" rpm signal you can tap into. Any signal that changes with rpm has to be processed by the gauge to convert it to rpm.

The wiring on the primary side of the coil sees a voltage and current spike when the plug is fired so if either is measured, the meter has to measure the frequency of the spike and multiply it by two to get rpm. (On a coil-on-plug 4-stroke engine, it doesn't matter how many cylinders the engine has, the coil fires every second crank revolution.)

Voltage can be measured by tapping into the primary side wiring but the meter has to be capable of handling the 400 volt spike created during the firing cycle. You can get current with a clamp-on ammeter.

The secondary side of a coil was the favourite place for dyno shops to pick up an rpm but again it needs a clamp-on probe and some logic to create the rpm. And the M5 secondary wiring between the coil and the plug is inaccessible unless you install a temporary extension.

To get an rpm signal from the DME needs some type of OBDII scanner to pick out the rpm signal. And even if you have that, the refresh rate through the BMW diagnostic port is too slow to be useful.

A few aftermarket tuning tools like the LM1 wideband O2 sensor pick up the rpm from the frequency of the ac ripple on the 14V generated by the alternator. Maybe the meter can do that. If it can, that just requires plugging a meter input into the cigarette lighter.
 
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