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330ci Intermittent Staling/Failure to start - poss fuel pump?

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Hi all, 

New to the forum and e46 ownership - figured it was a good idea to join this community to tap into the knowledge, and what better time than with my first issue!facepalmsmiley.gif

Situation is - car has begun randomly failing to start - cranks absolutely fine but no fire, in the past if I've left it and tried again some time later it's suddenly started. Started to think it might be the fuel pump/fuse/relay. (also tapped the tank underneath the last time and it started straight after, but could be coincide)

The other day it stalled while driving and wouldn't restart - had it recovered to the garage where it obviously started first time, showed no fault codes and has subsequently run fine ever since BUT.. while driving, if I'm stationary at lights for example, i can intermittently hear a whir/buzz sound, sounds like its coming from the rear and could possibly be a struggling pump (although i may be creating that connection in my head!!)

Checked the fuse under the bonnet, had the relay swapped - noise continues but so far seems fine (although I've kept the tank full above a quarter ever since)

My question is two fold - has anyone experienced anything similar and could share and secondly, if i go ahead and swap the pump out as a guess, does the car have an internal fuel pump accessible via the underneath of the rear seat? I've seen a few things suggesting this is the case on the Coupe, but mine is a convertible and someone suggested i'd have to drop the tank. I'm reasonably handy with a spanner but space/cover is an issue so tank dropping would be far more difficult!!

Car is a 2003 330ci (e46)

Any thoughts/suggestions/advice would be greatly appreciated!!

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Hi there, I have same car (2004 330ci covertible) and I did my fuel pump last month. Took about 30min....and it only took that long as I couldn't find some snips to get the fuel pipe clip off the old pump. Especially easy with the conv. as you just drop the roof and you have loads of room to work.Oh and yes the pump is under rear seat on drivers side, just remove the cover plate and there it is. Car had similar symptoms you describe only getting worst then wouldn't start at all. I managed to get home the last time by getting someone to crank the engine whilst I knocked the fuel tank from under car.I think they just wear then the impeller gets stuck on a high spot...so knocking the tank dislodges the impeller and it can spin. Only worked once but I got home ok!! Phew! Good luck

Edited by AndyC_67

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When you turn the electrics on for the first time, you should hear the fuel pump under the rear seats prime fuel into the fuel rail. It pressurises to around 50psi then turns off. If you turn off and then turn on again it shouldn't prime again because there's a non-return valve on the fuel pump which prevents the fuel from returning to the tank. This allows for quick starts and should take several hours to completely drip back to the tank.

There's a valve on the fuel rail where you can measure the pressure. But if you turn ignition to 2, let it prime then turn off, use a small screwdriver to push in the middle of the valve and you should get a small spirt of fuel. If you get this then you know the fuel is pressurising correctly. If you wait a few minutes after turning off and then press in the valve, and there's no spirt, then the non-return valve is probably passing and allowing fuel to return to the tank. You'll need to replace the pump as it's not a part you can replace on its own.

Sent from my SM-G920F using Tapatalk

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