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Fuel Pump Relay

Old 05-17-2018, 11:46 AM
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Default Fuel Pump Relay

2003 LW300 6 cylinder 3.0

My problem: Intermittent start; motor cranks but does not always start.
Solution I have been trying which seems to work: turn ignition key to on but do not try to start motor for 5-10 seconds. After this attempt the car starts.
My question: Does the Fuel Pump Relay go bad all at once or slowly over time?

Also, the safe way to remove Relay from fuse box?
Old 05-17-2018, 10:55 PM
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Don't know the history of L car fuel pump failures, but it sounds like it is taking longer than it should to build up sufficient fuel pressure in the system such that the engine will run.
I have had the exact same issue on my 97SC2 which was notorious for fuel pumps with this defective design where the fuel pressure bleeds off in between starts.

Have you changed the fuel filter anytime recently? A fairly clogged up fuel filter acts as a pressure frop on the way to the furl rail under the hood where the injectors are.

You can do a loan a tool from Autozone or similar (leave deposit, get it back upon tool return) for a fuel pressure gauge which you can attach to the port on the fuel rail under the hood.
This will allow you to
1) monitor the KEY ON Pressure Buildup rate and the final pressure built before starting.
2) Compare the fuel pressure in 1) to the fuel pump spec
3) Figure out if the pressure is bleeding off by putting on the gauge, starting the car, running it for a few minutes, noting the running fuel pressure and comparing it to spec, then turning off, noting the OFF fuel pressure and figuring out the rate at which the pressure is dropping (if it is). Most fuel systems (more so the pumps) have a bleed off spec in addition to a pressure spec and flow spec.

If you haven't changed your fuel filter in the last 30K I would probably suggest that -- you can do the tests before and after to confirm if it was the issue making the fuel pressure drop just low enough that the fuel pressure was insufficient to start the car, which usually requires a rich mix.
Old 05-18-2018, 04:33 AM
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Thanks for the suggestion: I haven't changed the pump and I don't know if it ever has been changed. It's a job I can't attack, I believe the tank would have to be lowered.
I've been turning the ignition key to on, waiting 5-10 seconds, then cranking and the car starts right up every time.
No codes come up.
The thing I don't get is why the engine runs fine once started. Again. I have a concern about the Fuel Pump Relay at startup.
Old 05-18-2018, 08:51 AM
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Location: Lake Wales, FL
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It might not be the fuel pump itself, but a faulty fuel pressure regulator. Do like derf suggested and get a loan a tool from the zone and check the fuel pressure. If it drops, the zone had the fpr. Here it is.
Old 05-24-2018, 11:09 PM
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Advice given.

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