12v ignition back feed

[Elliott Scott1436215391]

Just wondering if someone can help out with a ingnition back feed issue I am having. I am have the engine run on after turning the key off. The engine is not running coorrectly when it is switched to the off position, the revs come up to around 1500rpm. I have my friend help try and find the problem and we thought I had solved it but it comes back still. The issue has only progressed since the install and tune of a G4 xtreme.

I have tried to install diodes in the ISC 12V supply with not luck. Placed one in the fuel pump 12V supply and burnt it out so thinking that the Amps drawn from the pumps is to great for a diode. Not sure if a diode in the 12V feed is the right position or is it ment to go in the switching 12V supply? I have only fuel pumps and ISC as auxliary outputs so not sure what to do now.

Cheers

Wombat

 

[Andrew Cripps]

Hi Wombat

Just reading you post here, sounds like you are driving the fuel pump directly from the link, while im not sure about the xtreme, the usual way to wire the fuel pump/s is to install a relay to drive the pumps. this takes the load off the link itself as it only has to drive the coil of the relay, NOT the full load of the fuel pump/s, thats why the diode burnt out and may have damaged the computer (but im sure the gurus at link will confirm this). as for the run on, im not sure what that could be.... hope this helps.

[Elliott Scott1436215391]

Cheers for the comment Andrew. I have wired up the fuels with a negative trigger off the Auxilary Outputs via a relay. I have a few relays setup in the 12V power delivery, and all are negatively triggered by the computer. The only one seperate is the main ECU relay which is cranking ingition triggered relay and then this one feeds power to the other relays coils. The diode for the fuel pumps was in the 12V feed straight to the pumps. I am running twin bosch pumps so I am assuming that the amount of Amps drawn by these pump would be rather great and the diode only was a 5 Amp one.

Cheers

Wombat

[Top Tune NZ]

check you are using ignition switched 12v for the relay power. and not looping the main 12v over on the relay  or this will cause a back feed like you have also dont loop wires from one relay to the next relay

confusing aye

 

[Matt Dunn]

I had a real issue with tis too a while ago.

It is quite confusing and took me a while to sort it as it was in how I had wired the car.

 

If you have power from the ignition switch feed the ecu power and also feed a relay windings,

and that relay switches on someting that is negative triggered by the ecu like a boost solenoid, VVT soleoind etc,

then it creates a loop which stops that relay and the ECU from turning off.

 

Easiest way to make sure you have no problem is make sure that there is no voltage on any of the ECU pins with the ignition off,

and use a relay to switch the ign feed to the ecu that triggers nothing else.

 

.