Question?

[siteunseen]

Could I put a carbureted motor in my '77 280 and disconnect the ECU and harness, leaving it in the car? Does the ECU control more than the engine?

[Jeff G 78]

The ECU only controls the engine. You are safe.

[SteveJ]

Well, what all are you thinking of doing with the swap?

The ECU controls the electric fuel pump. If you keep the electric fuel pump, you would need to add your own relay control for it since the fuel pump is triggered by the AFM in the 77. You would also have to reduce the pressure, too.

If you disabled the electric pump, you would need to remove the blocking plate and add a mechanical fuel pump.

[siteunseen]

Thank you Jeff, I don't want to mess with the 240, it's part of my 401K.

EDIT:

Thank you too Steve, I wasn't sure about the pump. I've got Weber's and will probably get a Holley Blue.

Edited April 10, 2013 by siteunseen

[Jeff G 78]

I wouldn't try to use the stock FI pump for carbs. Either use a mechanical pump or install a low pressure electric pump.

[LeonV]

Thank you Jeff, I don't want to mess with the 240, it's part of my 401K.

EDIT:

Thank you too Steve, I wasn't sure about the pump. I've got Weber's and will probably get a Holley Blue.

The stock EFI pump would flow plenty at 3psi. Setup your regulator to regulate backpressure and the pump will be quiet and reliable. This is assuming that 280Z fuel feed and return lines are the same diameter.

[Captain Obvious]

The ECU controls the electric fuel pump.

I'm sure it was a simple use of the wrong acronym, but for the sake of clarity and completeness, the above is incorrect. It's not the ECU that controls the fuel pump, it's the AFM and the fuel injection relay (above your left knee under the dash) that control the fuel pump. You could completely remove the ECU from the car and if you lift the AFM vane, the fuel pump will run.

But back to the real point... Other than the fuel pump, I don't think there is anything else that you would have to spend any attention on when converting to carbs. The FI harness is it's own entity and separate from everything else. The only things it makes contact to are FI specific components and the battery.

[SteveJ]

Actually, what I should have said is that the ECU provides the ground for the fuel pump relay.

[Captain Obvious]

Actually, what I should have said is that the ECU provides the ground for the fuel pump relay.

Nope. The ground for the fuel pump relay is hard wired on connection #72. The ECU really has absolutely no direct link to the fuel pump operation at all.

The only link between the ECU itself and the fuel pump operation is indirect. By that, I mean... The engine won't run without the ECU and the vane in the AFM won't close the fuel pump contacts unless the engine is running. But other than that, there's no link. In short, the only way the ECU controls the fuel pump is through the use of air.

Remember, we're talking 77 (and prior) here, but I believe the above applies to 78 as well. You would just have to change references to AFM to oil pressure switch instead.

[SteveJ]

Dang it. My bad. I did a crappy job of tracing it. I only followed it up to Pin 5 on the ECU and assumed that the ground when from Pin 5 to ground through the ECU chassis. Thank you for the correction.

[Captain Obvious]

Haha! Yeah, I figured as much. I know you know your stuff and it had to be something simple like that.

[siteunseen]

I feel like I just had a beer with you guys. Thank you.