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

[fphil]

yes, it dépends on how things can be wired

[Wolf_Tm]

What about connecting a resistance to drop this 4V Under the threshold voltage of the relay? Or else you could upper the thereshold with a diode.

why just not make relay supply die when ignition is off?

I already tried to install a 2nd relay (activated by the Main Relay) on the Fuel Pump relay Positive, but even the 2nd one just gets activated by the Flyback!
And if I move the 2nd relay activation wire from the Main Relay to another switched source, then the engine will not start because during cranking the relay will get off.

[smurfinator]

What about connecting a resistance to drop this 4V Under the threshold voltage of the relay? Or else you could upper the thereshold with a diode.

why just not make relay supply die when ignition is off?

This is what I did on my 3.6 board since having problems of this nature with my (um...fried) 3.3 board.  Nothing in the car gets power until the main OEM power bus relay is switched on by the key.  So, there are cascading relays in order to get power: Turn key > main OEM power bus relay ON > VEMS unit power relay ON > fuel pump relay ON.  Fuel pump relay is in the boot with its fuse and not on the main (aftermarket)  fuse panel, so the pump draws straight from close proximity of the battery with its own heavy cable and chassis ground when the relay is ON and only when all the other stuff is on.  So, if I blow the 1 amp VEMS fuse, fuel pump turns off.

[Wolf_Tm]

I think your magic trick will be to insert a 18V zener diode.

And it was! It worked wonderfully, thanks!!!

[grillage]

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!

[Wolf_Tm]

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!

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

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.