540i hard to start / extended cranking

[alex418]

Hi all,

I'm hoping I can get some help troubleshooting before I throw money at expensive parts. My 2002 540i has a problem with taking a long time to start. Once it is running, it's fine, no warning lights or code, smooth idle. To start it, I can either turn the key for a while (~5+ seconds) or hold the key for a couple seconds, turn the car off, and then crank a second time. It always starts, but this is getting annoying, and I'm sure I'm killing the life of my starter by continuing to do this.

This issue is 100% reproduceable and dependent on how long the car has been sitting:

Sitting for a few minutes (filling up at a gas station) = issue doesn't occur, car fires right up
Sitting overnight (or longer) = issue occurs, sometimes a bit of smoke comes out tailpipe
Sitting for 1-4 hours (this is a bit of a guesstimate but I've definitely noticed this happening after only an hour of sitting) = issue occurs and car usually runs like shit for a couple seconds / smoke comes out tailpipe


To me, all of this screams "fuel pressure issue", but both fuel pumps and injectors are expensive, and I'd rather not buy both. I know my fuel pump was replaced prior to my ownership, approximately 20k miles ago. Based on the price (~150) I assume it was not with an OEM unit.

The car has new plugs, coils, and fuel filter / pressure regulator.

Has anyone encountered this problem before or have suggestions?

[JimLev]

Get the fuel pressure checked, should be about 52 PSI when the engine is running and only drop 7 PSI in 20 min after you shut the engine off.

[seagreen323i]

When I had this issue it was a small fuel leak at the fuel filter. Drained the lines overnight and had to re prime to start up fast.

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[dtw]

Sounds like rail pressure is bleeding off. Check pressure at rail when cold and watch as you crank.

[TiesTorN]

injectors may be leaking. does it sputter while cranking?

[Chedley]

I have exactly the same problem, after a long drive in a snow storm. I had to tow the car to a shop. Any quick fix to get it back on the road ? ( I am stranded out of to town)

[JimLev]

Need more info. Out of gas, battery/alt dead, intake full of snow?

[alex418]

Get the fuel pressure checked, should be about 52 PSI when the engine is running and only drop 7 PSI in 20 min after you shut the engine off.

Well this has given me an excuse to finally own a fuel pressure gauge.

It's reading around 47 psi while running... which I've read is within spec (47 up to 52 psi as you said.)

I set a timer after shutting the motor off and after about 4 minutes it had dropped down to 0.
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[JimLev]

Even 47 while running is too low. Without looking it up I think the spec is 52 +/- 2 psi.

[alex418]

Even 47 while running is too low. Without looking it up I think the spec is 52 +/- 2 psi.

Bentley says 50.76 +/- 2.9 psi, so I suppose I might be somewhat low, but I'm more concerned about losing all fuel pressure after 4 minutes of the car being off. I'm using a Harbor Freight gauge so it wouldn't surprise me if it's simply inaccurate by 1 or 2 psi.

I also took the test at the Schrader valve on the rail, not like how they pictured it there. Not sure if that could cause some discrepancy.
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[JimLev]

Regardless of your actual reading it should not drop to 0 in 4 min.

[alex418]

Regardless of your actual reading it should not drop to 0 in 4 min.

Right. I'm leaning towards it being a leaky injector. Or injectors frankly. I'd just like to be able to confirm it before dropping the $350 on a set.

[JimLev]

You could pull the fuel rail out with all the injectors attached (electrical connectors disconnected) then cycle the key on/off a few times to check them for leaks.

[alex418]

That's a great idea, I'm going to try that tomorrow.

[Deadwake]

Right. I'm leaning towards it being a leaky injector. Or injectors frankly. I'd just like to be able to confirm it before dropping the $350 on a set.

I'd be surprised if your injectors are cracked or anything, if they are leaking you should only need to replace the o rings on the top and bottom... A fairly tedious process but not hard. If you do need some injectors and dont want to drop money on brand new ones I have a set of 8 I pulled off a parts car. I warn you that that car was abused by the previous owner. Tons of sludge in the motor, I wouldn't be surprised if those injectors spent their lives spraying the cheapest fuel the owner could find.

[dtw]

I'd be surprised if your injectors are cracked or anything, if they are leaking you should only need to replace the o rings on the top and bottom... A fairly tedious process but not hard. If you do need some injectors and dont want to drop money on brand new ones I have a set of 8 I pulled off a parts car. I warn you that that car was abused by the previous owner. Tons of sludge in the motor, I wouldn't be surprised if those injectors spent their lives spraying the cheapest fuel the owner could find.

The referenced leak would be an internal injector leak (fuel leaking into the cylinder and draining down the rail pressure); this can only be 'serviced' by ultrasonic cleaning but often fails. The o-rings you mention seal the injector and intake against atmosphere and will not help in this situation.

Alex418, if indeed you confirm failed/leaking injectors, please consider checking your cylinders with a boreoscope (excellent, low cost options on Amazon). Constantly washing the cylinders with fuel can quickly degrade the cylinder walls.

[alex418]

Well then for the sake of my cylinder walls I'm happy to report that after 2 key cycles I have 8 dry shop towels underneath my injectors.

At this point being as I've already changed the FPR/filter, I suppose I'm looking at a bad fuel pump?

[demetk]

I suppose I'm looking at a bad fuel pump?

you can test for a leaky fuel pump check valve by clamping the rubber fuel line going to the fuel rail. That should tell you if the injectors are leaking if the pressure drops or the fuel pump check valve has failed if the pressure doesn't drop.

[alex418]

I'm happy to report the starting issue has been resolved after buying a cheap 8mm inline check valve and installing it right in front of the fuel pump. Eventually I plan to replace the fuel pump with an OEM one as I'm not a fan of whatever cheapo aftermarket the previous owner installed, especially as the check valve in it has failed already. But this works as a temporary solution for now so I don't have to be "that guy" who's car doesn't start at the grocery store.

I also swapped in a "Hengst" brand FPR/filter and am now seeing ~52 psi at idle as opposed to 47 psi previously. So let that be a lesson to not be an idiot like me and do NOT put the cheapest Rock Auto filter/FPR on your car.

Thanks to everyone who assisted!

[seagreen323i]

Glad you got er goin!

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[Chedley]

Good to hear you got it running.
Is the fuel pump the original on this car ? Never replaced ??

[alex418]

Good to hear you got it running.
Is the fuel pump the original on this car ? Never replaced ??

It's been replaced twice prior to my ownership. Once at ~120k, once at ~125k. The car currently has ~143k. I don't know the brand beyond it not being OEM. Fuel pumps are one case where I always like to pay up for an OEM part.

[Chedley]

So, I am still on my original fuel pump -never touched it or replaced it.

But,...
No to steal your thread, in my case (2001 540i V8) the problem appeared last week when I took a long 300 miles ski trip in a snowstorm. I parked the car in sub-freezing temperatures for 2 days. Then it refused to start. So I have it towed to a local import cars mechanic shop.
We did nothing other than refilling it with high octane gas, and pouring 2 quarts of 10W40 racing motor oil.
And that was that. The car starts, runs and the engine purrs like a happy cat….!! Go figure.. (the mechanic wrote something about the Vanos clogged in cold temp ?)....

[seagreen323i]

My pump is factory on both of my cars

540 at 196k miles

323i at ??? Because the odometer has been busted forever. If I had to guess at like 270k

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