My aftermarket ECU is tapped it to the connector for the stock ecu. . Does anyone use a relay to boost the supply power to their ecu instead of just using the stock source? I think that my ECU could be starving for power. The symtoms show up in the data logs. At high boost high rpm I notice the logged Battery voltage drops approx .5 volts(Alternator in good condition). My theory is that at this high boost/rpm the injectors and other ecu circuits are at high duty and could be pulling more power than the available supply thus causing a power drop across the ecu. I also notice that my tps reading will drop from 100% down to about 94% even though I am at full throttle.

If this is so, could installing a relay with heavier wires directly from the battery solve this?

 

You can. But I would trigger that relay using the same signal that is used stock--similar to a fuel pump rewire.

 

.... mate setting up a relay isnt going to solve your problem then.. what ecu are you running ?

 

Why not?.......... Is it not possible for an ecu to be under supplied with current, which then will affect its systems?

 

What system are you using?

Is the power for the fuel pump, injectors, and ignition being drawn directly through the ECU? They should have their own circuits, drawing current through their own relays. The ECU itself isn't doing much in the way of "powering" these circuits.

 

^^ what he said.

I guess it is possible to under supply the power to the ecu. But a relay doesnt supply more power and fix the problem if their was one.

 

The relay will supply more power if it is getting power from a stronger source than the existing power source to the ecu.

I just need to know if there are others who use a relay to power their ecu.

 

.

 

Ems 4424

 

I reckon the voltage in your car is dropping half a volt and you need to sort out your alternator. Put a more powerful one on their.

 

As I mentioned before, the ECU itself (EMS 4424 specifically) doesn't power the coils, injectors, or fuel pump. There is nothing within the ECU itself that is going to pull significantly more amperage than the stock ECU, so using the stock ECU circuit to supply the aftermarket ECU is completely plausible. You will not sort your voltage issue by providing a higher amperage circuit to the ECU itself.

RX72C is most likely correct. You have an overall electrical issue. Under boost amperage loads can become quite high, higher than they are under low loads. It wouldn't be the first time a weak alternator or poor alternator and/or battery wiring caused an issue like this.

 

Thanks for the responses guys

 

Most of the ECU's outputs are switching ground, for instance the injectors get +12V power from a relay and the ECU sends a switched ground signal to activate them. If anything, you may want to make sure the ECU's ground wire(s) are in good shape. It's possible there is too much resistance in the wire(s) and connections between the ECU's ground pin and the battery negative terminal, this would cause the same effect on an ECU datalog.


From what I remember, the stock '94 RX-7 wiring harness connects the ECU ground wires to a bolt in the engine bay (possibly on the UIM?), not directly to the battery negative post. It may be a good idea to ensure that this connection is sound and that the engine is grounded to the battery well.

 

Very good point.......I will look into it.

 

This is absolutely correct. He speaks the truth. (The only exception I can think of is if there are new ignition amplifiers (i.e, CDI) associated with the ECU--which may need to be sourced power separately.)

 

Excellent point!

 

I want to have his baby!