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

Started by gunni, December 05, 2014, 04:45:52 PM

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fphil

yes, it dépends on how things can be wired

Wolf_Tm

Quote from: Kamuto on December 28, 2016, 05:34:12 PM
Quote from: fphil on December 28, 2016, 04:59:56 PM
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

Quote from: Kamuto on December 28, 2016, 05:34:12 PM
Quote from: fphil on December 28, 2016, 04:59:56 PM
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.

Audi ABZ 4.2 V8 in 1993 90 quattro
TTV 60-2 flywheel and cam sync
firmware: 1.2.20

Smurf blue (BMW Laguna Seca), hence the name!

Wolf_Tm

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.


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

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!

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

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.