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Discussion Starter #1
Hi All,

I am experiencing a strange - at least to me- problem with my ignition. So when I start the car in the morning to go to work everything goes very smoothly. If I park the car and try to start it within 10 minutes or so again everything is still ok.

Now if I leave the car for around two hours and try to start the ignition , it does not start immediately. Sometimes I have to try it again or keep the ignition turned a bit longer for it to work.

This leaves me quite baffled. I don't think the symptoms fit a battery or alternator issue, though I certainly could be wrong.

If anyone has any ideas on this, I would greatly appreciate your input.

Regards
Rob
 

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does it crank normal, but just takes a lot of cranking? or does it not crank normally?
 

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if cranking is normal i'd be more suspicious of fuel supply. Pump going bad, perhaps. Possibly you have some leaky injectors that flood the combustion chambers when the car is shut off.

Based on normal cranking i'd not suspect battery or charging system
 

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Discussion Starter #5
if cranking is normal i'd be more suspicious of fuel supply. Pump going bad, perhaps. Possibly you have some leaky injectors that flood the combustion chambers when the car is shut off.

Based on normal cranking i'd not suspect battery or charging system
Ok, but if it was the leaking injector or fuel pump (which btw was replaced in 2011) would that not be problem when the car is parked for a longer period of time?
 

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if it was a leaky fuel injector, after being parked for several hours, the fuel rail will be depressurized, so leak will dissipate and after sitting for a while the residual fuel would evaporate away. That's my thought process at least.

For the pump, i'm thinking a heat soak issue may be causing an issue. But just thinking out loud.

Maybe drive the car, let it sit for a couple hours and pull the plugs out to see what they look like.
 

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Discussion Starter #7 (Edited)
if it was a leaky fuel injector, after being parked for several hours, the fuel rail will be depressurized, so leak will dissipate and after sitting for a while the residual fuel would evaporate away. That's my thought process at least.

For the pump, i'm thinking a heat soak issue may be causing an issue. But just thinking out loud.

Maybe drive the car, let it sit for a couple hours and pull the plugs out to see what they look like.
I see what you are getting at with the car being parked for a longer period of time.

However the restart after a few minutes is fairly smooth, so in case of a leaky injector should the symptoms not be be the same wether the car is turned off for a few minutes or couple of hours?

Sorry for all the follow up questions, I am obviously not knowledgable on the subject :biggrin:

Cheers,
Rob
 

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Fuel pump; FUEL FILTER???

As far as I know :blabla: ... just some more thoughts in addition to the posts above ...

... the fuel pump relais starts the fuel pump as soon as a crank signal comes fom the CPS crankshaft position sensor
... if the CPS would not operate properly the engine would not run at all (or with permanent limited performance)
... if one or two injectors would leak the other 4 or 5 cylinders would start?

So how about the fuel pump or - even more likely - the fuel filter ?

FYI I exchanged my fuel filter just by chance this year and found out that it was nearly full of a dirty water-fuel mixture - no malfunction yet but this would have been just a matter of time.
 

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Hi All,

I am experiencing a strange - at least to me- problem with my ignition. So when I start the car in the morning to go to work everything goes very smoothly. If I park the car and try to start it within 10 minutes or so again everything is still ok.

Now if I leave the car for around two hours and try to start the ignition , it does not start immediately. Sometimes I have to try it again or keep the ignition turned a bit longer for it to work.

This leaves me quite baffled. I don't think the symptoms fit a battery or alternator issue, though I certainly could be wrong.

If anyone has any ideas on this, I would greatly appreciate your input.

Regards
Rob
Get a pressure gauge on the fuel rail.
I also suggest, you not drive the car much (certainly no near or WOT runs) until it is repaired!!!
The fuel pump and fuel pressure regulator both can cause long crank problems.
The fuel pump/pickup has a check valve that prevents the fuel in the fuel supply line and pressure from leaking back into the tank once the pump stops, not too harmful to the engine.
However, the fuel pressure regulator controls the fuel returned to the tank and it should maintain the specified fuel pressure at all times 1) so the injectors have the correct pressure to start the engine and 2) to insure the injectors meter out the correct fuel for the injector pulse regardless of the intake manifold vacuum.
If the fuel pressure regulator is not holding the fuel pressure when the pump is off it is most likely not controlling the desired dynamic pressure across the injectors (pump pressure on one side and intake vacuum on the other) when the engine is operating. This is of great concern because the engine usually will run lean at times and that is a No-No for the M5 because it can very quietly destroy pistons due to detonation.
An easy diagnostic, is to just replace the old fuel pressure regulator as Preventative Maintenance since they don't last forever and if you don't know when it was replaced it is most likely the original and is overdue anyway.
 
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