Technical > Wiring & Sensors

Fuel pump relay staying on when VEMS powered OFF through P259 output

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Wolf_Tm:

--- Quote from: grillage on September 12, 2019, 10:40:39 pm ---Bringing this back from the dead - I have the same problem. Where was the zener diode installed to fix this? Ahead of the fused 12v to VEMS? or elsewhere?
thanks!

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--- Quote from: Mads Lund on December 27, 2016, 11:47:52 pm ---I think your magic trick will be to insert a 18V zener diode. They work in a way, that current will flow in one direction, and no current the other way (like a normal diode works) but when the reverse voltage exceed the zener level (eg. 18V) can current flow in both directions.
In your case, where a protection diode potentially make current flow from a relay power back toward the FET, throu a protection diode, and back to a mains somewhere, can a zener allow the spike protection, but stop the reverse current a normal voltages (12-14v).

It's a common issue when the design controls the electornics on both the positive and negative side. Even I thougt that I was carefull when I designed the complete loom for my TVR, did I end up with the nice feature that turning on the long beam, with the key out... made the ECU power up..... a couple of hours and a few diodes later, did it work as expected :-)

Injector flyback, that is powered from the injector +12V should normally not have power without the ECU is on power, Either by using the same relay for both injector + ignition + ecu power, or by powering the injector and ignition with the fuel pump relay

Br Mads

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In the injectors Flyback wire

grillage:
Thanks,

To clarify, where exactly in the Flyback Wire?


A, B, C or D?

And if A, which direction should the power flow go? Toward or From the ECU?

Thanks again,
Ben

msh:
A, and likely from the ECU, after all, the purpose of flyback is to drain inductive power spikes from outputs, using diodes to isolate FET outputs from 12v, at the same time allowing voltage spikes from injectors to flow to cars electric system.

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