HELP - Fuel Problem

[songzunhuang]

I have been struggle with a situation where my engine is not getting fuel I posted details in "My Project".
I'm putting a link here in hopes that someone will see it faster. Thanks.

Link: viewtopic.php?p=236946#p236946

[marc79euro645]

I'd start at the pump, and double check that your not getting the voltage. It could be the pump.

[songzunhuang]

I'd start at the pump, and double check that your not getting the voltage. It could be the pump.

First, I appreciate your reply. I replaced the fuel pump with a new Bosch unit in February 2022. So it's only been about 10 months. I don't think that's the culprit. Also I did a lot of tests with regards to the pump. Pump runs fine when jumpered 30 + 87 at the fuel pump relay. Also the motronic connector pin 20 is the fuel pump relay control. I can hear the fuel pump kicking in when I ground pin 20.

If I run the fuel pump manually to pressurize the fuel rail, the car starts every time and runs for a few seconds. It just won't run with the fuel pump relay in place. I can't even keep the motor running when I jumper 30 +87 to force the fuel pump to run.

Something is shutting off the fuel pump when the motor starts. It's quite vexing.

[TimU]

Song, I read your other post too.

This sounds like a classic fuel pressure issue.

Symptoms:
1. It won't start without manual pump (lack of pressure to start)
2. It starts after manually jumping the pump for 5-10secs (to pressurise the rails)
3. It dies shortly after starting (lack of pressure to keep feeding)

Suggestions:
- Install a fuel pressure test port at the fuel rail inlet line.
You should have 42psi at idle.
If not, check/replace your Fuel Pressure Regulator.

- test the fuel pump flow rate at the HP pump outlet (into a bucket). It should flow 1L per 15secs or there abouts.

- check the flow rate after the fuel filter.
Flow rate should be similar. I've seen filters fail internally and block the flow.

- Check the LP pump in the tank for blockages and function.

Good luck, let us know how you go.

Tim

[TimU]

This is what I installed in my Fuel line to test FP

[songzunhuang]

Song, I read your other post too.

This sounds like a classic fuel pressure issue.

Symptoms:
1. It won't start without manual pump (lack of pressure to start)
2. It starts after manually jumping the pump for 5-10secs (to pressurise the rails)
3. It dies shortly after starting (lack of pressure to keep feeding)

Suggestions:
- Install a fuel pressure test port at the fuel rail inlet line.
You should have 42psi at idle.
If not, check/replace your Fuel Pressure Regulator.

- test the fuel pump flow rate at the HP pump outlet (into a bucket). It should flow 1L per 15secs or there abouts.

- check the flow rate after the fuel filter.
Flow rate should be similar. I've seen filters fail internally and block the flow.

- Check the LP pump in the tank for blockages and function.

Good luck, let us know how you go.

Tim

Yes, I have also concluded that it's a fuel delivery problem. Furthermore, I think something is shutting down power to the fuel pump. Since all the wiring and tests show all is well, I have looked to the ECU.

BTW, the fuel filter was also changed when I put in the new fuel pump last year. So failure of the filter is improbable. I don't see any signs of fuel restrictions. Then again, I haven't formally measured it. I my do that just for kicks when I get the chance.

[TimU]

Pin 20 on the ECU controls the FP relay.
Pin 14 = Fuel Injector Controls (cyl 1,2,3)
PIN 15 = Fuel Injector Controls (cyl 4,5,6)

I'd be surprised if it was the ECU faulting here because you've already bypassed the ECU control of the FP relay (pin 20) by manually energising the FP relay socket.

Either way, you should be able to rig up a parasitic test wire on the fuel pump relay to measure what electrical signals you're getting when the engine dies.

If it's still a strong 12v signal, I would suggest that rules out the ECU or any electrical fault.

Then you can focus on troubleshooting pressure and flow issues.

[kronus]

note that the pump turning on may not necessarily mean that you are getting fuel. The pressure feed line may have come off the pump chassis, or the actual impeller may have disintegrated.

check your fuel pressure.