1995 BMW 325i convertible; very hard to start, runs great once started. Changed fuel pump, fuel pressure regulator, and ECM. It has to crank and crank before it almost starts, then it finally starts (sometimes it doesnt) very inconsistant.
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indicates fuel leak back and fuel pressure drop
check filter installation for seal not sitting properly, loose fuel line fitting , pump installed correctly (flow wise ), filter installed correctly (flow wise)
air getting in to fuel lines
the thing you are looking for is indicated by the initial hard start but when started runs ok ( good fuel to the engine eventually) and then by the fact that if the engine is allowed to sit for a long period the problem returns meaning that the fuel pressure is not being held
could even be a problem fuel pressure regulator allowing the fuel to bypass ( no pressure =hard starting) then gets enough pressure to run ok but allows that pressure to drain off over time
Fuel Pump - can you here the pump (usually under the right hand back seat) running with ignition on?
Fuel Delivery (injectors) - squirt some fuel (just a cap full) into the manifold.
Spark - pull a lead off a spark plug and use a spare spark plug resting on the exhaust manifold.
Crank sensor - Injectors won't inject fuel if the ECU thinks the engine isn't turning. Crank sensor is at the front right lower side and as it gets older, the wire gets brittle and breaks most of the time where it meets the hard end. The connector is under the throttle body and should read 500-600 ohms.
Just because you replaced the fuel pressure regulator does not mean it is working correctly; which is the most common cause of your problem. Hook up a fuel pressure guage and watch what happens when you are starting it cold - it should go up to about 47 PSI and once started it should read between 40-47 PSI, then when you turn the engine off: Does the pressure drop? There is a check valve built into the fuel pump also; that can be faulty and if the pressure is generally reading low and the check valve is bad- this can also create your problem. We have run into this before also; When the fuel pump is cold the internal pump seals are sealing great, but after a period of running time the pump seals lose sealing power and if you try to start it again it will be hard to start. The biggest thing with this situation is getting the fuel pressure readings at the following points of time:: Start-up, running cold, running at normal operating temp, engine off, engine re-start.
Pete/ Bambenek Auto LLC
install pressure gauge and watch when key is turned off to see if pressure drops to zero if so bad drain back valve in fuel pump replace it or deal with it or could be cheap aftermarket pump and has hard time building unnecessary pressure to open poppet valves between before fuel injectors
When you say that it tries to start but does not turn over - I interpret that to mean that the starter is cranking the engine, but the engine fails to start. Is that correct?
The ignition on these cars occasionally looses a single coil, but is not prone to loosing all ignition on all cylinders at once, so probability indicates that the problem is lack of fuel delivery.
This car is prone to two fuel delivery problems:
1) Failure of the fuel transfer pump that moves fuel from the driver side tank to the passenger side tank where the fuel delivery pump is located. If the car runs out of fuel when the gas gauge registers 1/4 full, and runs again if you add more fuel, this is the problem.
2) Failure of the fuel delivery pump. This is less common, but my wife's '04 330 lost a fuel pump at 80k miles, so it can happen.
I had same problem on 1996 gmc. It would start great and run great if you primed it with gas. The fuel pressure was at 55lb. It turned out itwas the fuel pump. The injectors on my truck needed more pressure to start but after starting this was enough pressure to run. I ran my truck for 4 months before the fuel pump quit alltogether. Once I changed the pump it started perfectly. Hope this is helpful. Sudbury, Ontario, Canada
It sounds like a faulty fuel pressure regulator. When you turn the key to the on position the fuel pump starts for an instant to build pressure in the fuel line. If the pressure regulator has allowed too much leakage since the last start then the fuel pump does not have enough time to prime the line. The fuel pressure will still measure ok when the car is running because the leakage is very low. Try turning the key off and on a few times prior to starting and see if the extra pump priming steps help. Also check the vacuum line to the regulator because it needs vacuum to work correctly.