Hotwire coil ecu pick up

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Lmy78k
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Hotwire coil ecu pick up

Post by Lmy78k » Sat Aug 11, 2018 11:19 am

Hi
Can anyone help I know the ecu picks up a pulse from the coil I think via a resistor inside the loom ive removed
Some wiring from the original discovery loom so dont want to connect to the coil without checking what is going in to the ecu I presume I can turn the engine over and put a meter on the wire whilst the ecu is unplugged what should I be looking for volts ?'resistance ?'
Thx



DaveEFI
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Re: Hotwire coil ecu pick up

Post by DaveEFI » Sat Aug 11, 2018 12:11 pm

The pulse from the coil negative is not something you can read accurately with a DVM. It is a flyback pulse caused by the collapse of the flux in an inductor - the coil. It can reach something like 50v peak or so. The early flapper system had an external 6K8 resistor between coil and ECU to limit the current - not sure about the hotwire. I'll look at my schematics later.
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GDCobra
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Re: Hotwire coil ecu pick up

Post by GDCobra » Sat Aug 18, 2018 9:23 pm

Lmy78k wrote:
Sat Aug 11, 2018 11:19 am
Hi
Can anyone help I know the ecu picks up a pulse from the coil I think via a resistor inside the loom ive removed
Some wiring from the original discovery loom so dont want to connect to the coil without checking what is going in to the ecu I presume I can turn the engine over and put a meter on the wire whilst the ecu is unplugged what should I be looking for volts ?'resistance ?'
Thx
The hot wire system does have a resistor in the cable (at least mine does ) which connects to the same coil terminal as the tachograph, if you've removed this cable from the loom can you not si ply measure the resistance of the piece you cut off?

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