Dcelone53

Hey all back with another question!

So I'm still workin on the street rod putting the ls400 engine in a 32 ford.

So jumping through the wires I got the car to fire! I've moved onto putting all the relays and a ignition switch in.

The car sparks and turns over but I have to bi pass the efi main relay and jump into it. The ecu isn't putting out power or grounding the terminals.

Any suggestions on what terminals arnt getting power or why the ecu isn't grouding?
Like I said, when I by pass the efi relay by jumping I get it to fire but the fuel pump relay isn't grounding to make the FP Work

I can give more info if needed!

Thanks

Yamae

You need to know some more how the ECU controls two relays for the fuel supply.

One is the fuel pump relay and the other circuit opening relay. The fuel pump relay is only bypassing the fuel pump resistor which is for normal engine running. I mean the resister is always passing the current to the pump and the fuel is supplied. The fuel pump relay only works when the engine is about to start or the load is heavy to supply more fuel giving the pump higher voltage.

On the other hand the circuit opening relay is controlling the fuel supply ON/OFF. When conditions to run the engine well are not enough, the ECU does not drive the circuit opening relay and the fuel is not supplied. Regarding those conditions, search the net and you will be finding them. The most common problem is a no connection of the MAF.

python

iTrader: (4)

http://www.underhoodservice.com/fuel...-current-draw/

Dcelone53

I probably,y need to be clearer, the engine right now is just sitting in a jig, I'm just doing some wiring for test purposes. One question first, what powers is ECU? According to the schematic, the efi main relay is powered by the ecu but no power is coming out, I can by pass it and out power there myself but it's eventually going to need to work

The ecu does ground the fuel pump relay correct? When I take the relay to ground w a test light you can hear the relay clicking...

Yamae

You need to understand that the ecu does not drive the fuel pump relay all the time. It only drives it at the start up and at the heavy load.

I don't understand you words,"what powers is ECU?".
You mean, "What is the power source of the ECU"? Those are all listed in the wiring diagram. There are 3 routes to supply DC12V to the ECU.

Dcelone53

I only ask what powers it because the ecu isn't sending out power to the main efi relay.

I don't have a fuel pump hooked up yet but with the test light, the switch doesn't close

Yamae

The main EFI relay is powered by the signal MREL of the ECU. The signal MREL goes up to 12V when the ECU is ready to work after checking conditions.

The ECU for the 1UZ-FE engine is not very simple. It sure needs some skill to analyze a black box.

randal

Dcelone, the ECU does NOT ground the fuel pump. The ECU controls a relay which can supply the full +12v to the motor or, when the relay is not energized, puts a resistor in series with the pump to limit the current.

So, there are actually three relays in the fuel pump path. One is the main EFI relay which gets energized when you turn the ignition switch to "on". There is a circuit opening relay and then there is a fuel pump relay which supplies voltage to the fuel pump itself. But the ECU in no way directly supplies either ground or power to the fuel pump. That makes sense because ECU's, being basically computers, generally do not drive a lot of power directly.

Now, the ECU does ground the relay coil of the fuel pump relay causing it to energize. But after the engine is running and does not demand high fuel delivery, the relay is dropped out and a resistor is placed in the path. As Yamae is saying, this is probably so that the pump does not overheat. Better to have the resistor take the brunt of the heat than the pump motor. MREL looks like a supply TO the ECU and FPR is FROM the ECU and grounds the fuel pump relay. You also have a Circuit Opening Relay which is controlled by the ECU. That relay is grounded by the ECU FC pin. It seems to be some sort of protection device, for instance, in case of an accident, the pump can be shut off so that fuel is not spewing out. At least thats what it looks like to me.

You will probably want to mimic the factory setup so that the ECU properly controls the pump.

Dcelone53

Alright I think I get it now ill test it out when I get a minute, thanks for being patient with me I'm kinda learning all the on the fly.

Appreciate the help

Dcelone53

Alright I think I get it now ill test it out when I get a minute, thanks for being patient with me I'm kinda learning all the on the fly.

Appreciate the help