Fuel pressure and starting car

[MFKN3]

Recently my car has been a bit hard to start, but only after sitting overnight or days.

It sort of half starts then a 3-4 seconds later, totally starts.

It doesn't do it if I turn the ignition on for a few seconds before starting, presumably because the fuel pump primes. So I am thinking the fuel pressure is draining back after the car has sat overnight?

Is that possible? Can anyone point me to things I should check?

[MilehighM3]

Check your fuel pressure first. The car primes the fuel system with an unlock signal, opening a door or trunk. Leave your hood open with the pressure gauge on it and check the pressure before disturbing the car after it has sat overnight or however long it takes to reproduce the issue. A good rule of thumb is that the fuel system should hold about 75% of its target pressure overnight.

Does the car start and run smooth after the extended cranking time or does it run rough? The 2 options for where the fuel pressure is bleeding off are either back into the tank or leaking injectors. Rough running would typically indicate leaking injectors.

[kenwelch]

If your problem is fuel supply related then you are trying to determine which component is causing the problem either the fuel pump check valve, the fuel pressure regulator or the fuel injectors. The max. running pressure spec is 6 bar.

Here is some direction from the technical and repair information.

BMW Technical Manual:
There is now only one fuel pump (the M5 has two). This has a three-phase motor, which ensures sufficient torque across the whole pump speed range. The pump speed is used to provide the required fuel pressure of 3-6 bar, depending on the engine operating state.
A fuel pressure sensor sends its signal to the MSS60. The fuel pressure sensor is located behind the inner fenderwell.
If the pressure sensor fails or there is a fault in the CAN bus and in the engine emergency program, the fuel pump is operated at full speed. In this process, the pressure is limited to 6 bar by the mechanical pressure sensor.

Mitchell Pro Demand Information:

Fuel System Testing > Residual Pressure

Fuel injection systems require a residual pressure to present after the engine is switched off. This allows the engine to start immediately after the vehicle has been parked.

If the residual fuel pressure diminishes after the vehicle has been shut off. Upon restart, there will be an extended cranking period before engine start. This is due to the fuel pump attempting to supply enough fuel for startup.

When the fuel system is at rest, there a three components which allow the fuel system to retain sufficient residual pressure. These items are, the fuel pump check valve, the fuel pressure regulator and the fuel injectors.


Complaint: starting problems
◦Run engine briefly at idle speed and switch off.
◦Note down measured value while engine is stopped.
◦Read off measured value again after approx. 20 to 30 minutes while engine is stopped.

Special tool 13 3 010 (hose clamp) is required for the following test.

If the measured value has dropped by more than 0.5 bar:
◦Start engine and wait briefly for a stable pressure increase.
◦Switch off the engine and immediately pinch off the delivery line just before the pressure gauge with the special tool 13 3 010 .
◦Note down measured value
◦Read off measured value again after approx. 20 to 30 minutes while engine is stopped

If the measured value has now dropped by less than 0.5 bar, the following faults can be present:
◦Fault in delivery lines
◦Fault in in-tank delivery hose
◦Faulty pressure-holding non-return valve in fuel pump

Check components. Replace faulty components.

If the measured value has dropped by more than 0.5 bar again:
◦Replace pressure regulator

[okusa]

I would think battery before fuel pressure.

[gobuffs]

Originally Posted by okusa

I would think battery before fuel pressure.

I was thinking the same. These modern ECUs don't like even slight dips in voltage. If the battery is weak and it drops to below 10v when cranking it will have a hard time starting if it does at all. Battery is an easy test point before going into fuel issues.

[MFKN3]

Thanks, this is perfect.

Charging battery was the first thing I did (it is also new).

I was going to put a pressure gauge on overnight and check. The car runs perfect once started.

[Exclusivs]

This is ironic, as I was just going to start a thread on this same thing. Attaching a video so you can see yourself.

Not a big issue, has always happened since owning the car. It is my daily now, but was not when I first got it, and the car sat alot (weeks without driving sometimes.)

Doesn't have the problem when warm, fires right up. Only first thing in the mornings, first start up.

Is a new battery needed?

[kenwelch]

In the video the cranking speed sounds normal. But the only real way to know is actually measure the cranking RPM and monitor the cranking battery voltage. Cranking voltage rule of thumb for a 12 volt battery is greater that 9.6 volts (about 10 volts) the battery is ok.

Battery capacity tests will also help when diagnosing battery issues. Kragen/O'Riely auto parts stores will often capacity test the battery for free. Just make sure they input the CCA (cold cranking amp) rating for your battery correctly. If the tester is set-up with a higher (incorrect) rating they will be selling you a battery.

If you have a battery charger, fully charging the battery before testing will improve the results.

[sylonien]

Not sure if this is the same problem, but mine did this recently.
Fuel was a bit low as you can see, car was hot and running fine prior to this.
Popped in to shop for a few minutes,
came out and it didn't start until I revved it.

Then I had tyre pressure, DSC, and engine error message.

Filled up with petrol and never happened since.

Did check the error codes and nothing suspicious,
except ...

279D DME: Power management, closed-circuit current violation
2B23 DME: Idle actuator governor monitoring, bank 1
5E19 DSC: Engine management: interface

Only done 20,000 miles. And nothing happened since that time.

At 23,000 miles as of today.
Battery always charged. Even though its still on the original 2010 battery.

[kenwelch]

Start by battery capacity testing. Eliminate the battery as a possible problem before wasting time with a long list of other possibilities. Codes and network errors can happen with low supply voltage which happens on a low capacity (worn-out) battery during cranking.

With dealer level software they can also look a the battery and start history to assist in battery diagnosis. A simple battery capacity test maybe all you need.

[dpgfunk]

Having a similar issue with my car, OP - any updates?

[MFKN3]

Not yet, I have it booked in at the end of the month before next time attack.

I rarely drive it now, I did start it yesterday though without turning ignition on first and it still does it. I'm convinced it's fuel pressure draining overnight.

If I turn ignition on for a few seconds, then start it, it's fine.

[MFKN3]

Originally Posted by Exclusivs

This is ironic, as I was just going to start a thread on this same thing. Attaching a video so you can see yourself.

Not a big issue, has always happened since owning the car. It is my daily now, but was not when I first got it, and the car sat alot (weeks without driving sometimes.)

Doesn't have the problem when warm, fires right up. Only first thing in the mornings, first start up.

Is a new battery needed?

Your video won't load but I think I caught it the other day and sounded normal to me

Originally Posted by sylonien

Not sure if this is the same problem, but mine did this recently.
Fuel was a bit low as you can see, car was hot and running fine prior to this.
Popped in to shop for a few minutes,
came out and it didn't start until I revved it.

Then I had tyre pressure, DSC, and engine error message.

Filled up with petrol and never happened since.

Did check the error codes and nothing suspicious,
except ...

279D DME: Power management, closed-circuit current violation
2B23 DME: Idle actuator governor monitoring, bank 1
5E19 DSC: Engine management: interface

Only done 20,000 miles. And nothing happened since that time.

At 23,000 miles as of today.
Battery always charged. Even though its still on the original 2010 battery.

Mine is similar but the starter motor doesn't stay on that long. The engine just half-starts, rumbles, then all cylinders kick in a few seconds later.

[gpxl]

MFKN3, What was the resolution for you? I'm having what sounds like a similar issue with my E90. Video here: http://www.m3post.com/forums/showpos...1&postcount=44

[JBG84]

I love when people start a thread asking for help with a complaint. Then never follow back to provide the outcome or resolution of the fault for others to learn from ��

[Honda]

Originally Posted by JBG84

I love when people start a thread asking for help with a complaint. Then never follow back to provide the outcome or resolution of the fault for others to learn from ��

If it is not battery or starter, it is probably a leaky fuel injector.