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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22145
Experience:  BEng hons Mech engineering, in auto industry 22 years
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BMW E46 318CI, misfires on start-up and under hard

Customer Question

BMW E46 318CI, misfires on start-up and under hard acceleration, spark plugs are new and all coil packs are working. what else could cause this
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.

Hello

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

Customer: replied 1 year ago.
is there only one fuel pump? located in the fuel tank?