808SC300

I have a 92 SC300 auto. Is it normal for fuel to be constantly flowing while the ignition is in the "on" position? This seems odd to me as I thought fuel would flow for a few seconds then stop as to "prime" the system. I have already replaced the fuel pressure regulator as well as the fuel pump ecu and none of these have solved the issue.

I have heard that fuel will only be constanly pumped if the pump is "hot wired". Any opinions/advice on what to do and what the problem might be will be most appreciated.

Thank you

gserep1

Hello,
Yes, the fuel pump is supposed to run while the engine is running, but not longer than 3 seconds if the engine is not being cranked. The fuel is controlled by the fuel pump relay and the crank sensor, and fuel pump ECU. When the key is turned to "on", the ECU energizes the fuel pump relay, and that cycles the pump on for 3 seconds to build up pressure for starting. The crank sensor counts the teeth of the flywheel and sends a signal to the ECU when the engine is turning. If the engine is not cranking, the crank sensor sends no signal to the computer, so the fuel shuts off after the 3 seconds.

Once the engine starts cranking, the computer receives a signal from the crank sensor. The computer sends a ground signal to the fuel pump relay, and the fuel pump continues to run as long as the engine runs. The pump has to supply fuel to KEEP the engine running, or the engine will die. It appears that the fuel pump is staying energized too long. I have a service manual for 99 and 2000 GS300 and 400's. I will try to help you if you would like.

Keep in touch!

Take care,

GSEREP1

808SC300

That's the thing, the pump continues to run even after a few secs while the ignition is in the "on" position and the engine is not running. I had changed out that fuel pump ECu to no avail and the car ran fine with the old ECU. The fuel pump ECU was not the problem, I'm guessing it's an electrical problem ....where I have no clue. Anyone else have some suggestions?

Faceless1

The fuel pump relay should be checked for continuity. If the relay has continuity on both sides then the relay is bad. What this simply means is that the relay is frozen on the on side of the switch and it will not turn off. Replacing the fuel pump relay should fix your problem.

Good Luck

808SC300

i've no clue where the fuel pump relay is located. I thought the fuel pump ECU was the only electrical component in the fuel system. Where can i find the fuel pump relay?