MSD relay issue with ECU

[ChasingSand]

Been chasing an issue for the last month. I recently went from relays for my fuel pump and fans to the MSD solid state relay.

I was using the ECU for the ground trigger for the fuel pump. Issue I am having is, anytime power is applied to the ecu it’s triggering the pump. I have checked my wiring 4X and also sent the ecu to diagnostic and they claimed it’s working as it should. I decided to try and wire in a standard relay instead of the MSD and the fuel pump worked as intended.

I undid the trigger wire and put it back on the MSD and the pump continued to run.

I tried two separate ports on the MSD with the same results.

Anyone experience this?

 

[Kraut_n_Rice]

You should note that it's an AEM Series 2.

 

[FlyinRyan]

Is your ecu trigger setting pulling high instead of pulling low?

 

[ChasingSand]

Is your ecu trigger setting pulling high instead of pulling low?

I was not aware this was an actual setting that can be adjusted in the AEM software.

 

[daveH]

I was not aware this was an actual setting that can be adjusted in the AEM software.

i thought about this, but the fact that you put a traditional relay in and it worked indicates the output is going low. assuming you had 12v on the other side of the relay.

 

[ChasingSand]

i thought about this, but the fact that you put a traditional relay in and it worked indicates the output is going low. assuming you had 12v on the other side of the relay.

So what I havw gathered is the MSD unit takes very little amperage to be triggered where a standard relay takes more. I was going to look into adding a resistor in line to the signal to try and avoid using a relay but I think the easier was is to just wire a relay inline and use the positive 12v output of it to trigger the MSD.

 

[daveH]

So what I havw gathered is the MSD unit takes very little amperage to be triggered where a standard relay takes more. I was going to look into adding a resistor in line to the signal to try and avoid using a relay but I think the easier was is to just wire a relay inline and use the positive 12v output of it to trigger the MSD.

you might try a pull down resistor. you do this by attaching one end of the resistor to the trigger wire and the other side of the resistor directly to ground. start with 1000 ohms. a lower the value of the resistor will "leak" more to ground and could keep the fan on all the time. some experimentation may be required to find the correct value.

 

[FlyinRyan]

Can you try setting up the output to high side instead. Just trying to simplify the wiring. Trigger it in the 12v bank on the msd.

 

[ChasingSand]

Can you try setting up the output to high side instead. Just trying to simplify the wiring. Trigger it in the 12v bank on the msd.

I would need to look in the AEM pin out and see if there is a high side fuel pump control. I am not sure if you can configure them in the software either.