Diesel starting problem

[Previously posted to uk.d-i-y]
Hi All
I've got a 7 year old BMW 530d and it has developed an intermittent starting issue. Normally, it will start with just a flick of the ignition, but now it
sometimes takes about 5 seconds. It turns over easily, so I don't suspect a battery problem. The battery however, is one that has a charge indicator, and it is black (insufficient charge). Of course it should be green, but at least it isn't orange (dead)!
Before this car I had another BMW diesel. When starting this one, you had to wait for the instrument panel's pigtail symbol to extinguish before cranking. This was, as you know, to allow the glow plugs to heat up.
The current car does not have this pigtail symbol, so how does it work? It still has glow plugs I assume? My thoughts as to the intermittent starting problem were that there is a loose connection to or from the glow plug relay. Any other thoughts before Mr Local 'tie me up and steal my money' BMW Dealer has a look? Oh, and if anyone knows where said relay is likely to be, that'd be useful too.
PS I've tried some BMW specific online forums, but these seem to have degenerated since I last used them ('where can I find an M3 logo for my 316?' etc).
Thanks.
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Oh yeah.
An it sounds like they're working. Now have a mercedes diesel (nd gas bmw) but the principles are the same. A diesel engine is a diesel engine.
Sounds like one or more glo plugs have died. Last year I was operating on 1 (ONE!) only and the othe four were completley dead. When the last one failed (of COURSE in february) it got REAL hard to start.
If ther's a way to test the glo plugs in situ I'd do that, it is not always possible depsning on the type.
But, if your plugs are original I think I'd just change all of them on principle. It's no worse than changing spark plugs usually. Use only BOSCH or Beru parts.
The other thing you might want to check and again I din't know how your engine is wired but there is a huge amount of cuttent going to those plugs and it's usually fused by something. Usually an 80 amp fuse that looks like it came out of your wall fuze box. These can fail even intermittently and it's cherap and easy to replace and a lot of people keep one spare.
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Richard Sexton wrote:

Thanks for the reply Richard. Problem is, I don't know how my engine is wired either! There must be, as you say, a large fuse and a relay to switch the glow-plugs on; I just need to find them.
What about a not-100% battery? Would that cause an intermittent start-up problem? (note that 99% of the time the engine starts quickly, only 1% of the time does it take much longer; and it cranks freely)
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Wellll, if the battery is more than 5 years old I'd replace it on priciple if you want to be toruble free. I *might* make an exception if it's an Optima or other gel cel battery but even they have limits.
You do need to attain a proper cranking speed to start a diesel but this is a function of temperature. And oil viscosity. Does it sound like it's cranking slower when it doesn't start right away?
I assume this only happens with a cold engine.
The fact it start fine most of the time tells me the compression is ok which is the only major problem you can find with something likt this.
I'd bet money on the idea you only have a couple of working glow plugs. Maybe only one.
Here's a thing I did a while back for starting diesels in the cold, whcih is more or less a roadmap of what has to be right for a dieel to start:
    http://articles.mbz.org/engine/diesel/coldstart /     http://articles.mbz.org/engine/diesel/morecold /
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Richard Sexton wrote:

Thanks again. Yes, only when cold. It cranks at the same speed whether it starts ot not, and it continues cranking at the same speed before it starts. My gut feeling (although a new battery is probably a good idea as the current one is likely as old as the car) is that it's glow-plug related; fuse, relay or plugs.
I'll post an update as it's off to our local garage for a quick check tomorrow.
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Grumps wrote:

OK. Our local garage has checked all possible issues and has found nothing! Of course, the engine starts perfectly at the moment. One thing they noticed was that the fuel filter is new(ish), and wondered if there was a fault with this or its fitting. How exactly does a fuel filter work, and what would cause it to sometimes stop the engine from starting?
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It filters out fine particulate matter that might clog the very fine openings of the injector nozzles.
It's just a paper element inside.
I can't say I've ever heard if this being a problem but in theory if it wasn't sealing right it could be leaking air intot he fuel stream.
When it does start after being piggy does it emit a cloud of black smoke?
Also, when it doesn't start it if after it's sat a long time?
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Richard Sexton wrote:

Not that I've noticed. But then, it's only 'not started' three times.

No, it can sit for a day and start perfectly.
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I had an intermittent start on mine recently - turned out it was an injector sticking open intermittently and the fuel was draining back to the tank - it took a while for the pumps (lift and injector) to get the fuel back to the nozzles - if it doesn't start immediately, stop cranking, turn off then on again without cranking, wait for ten seconds then crank - maybe repeat before cranking...
Nick
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I'd expect to see some black smoke from unburned fuel if it's trying to start, getting fuel, and can't. Hmm....
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I wonder if there are any check valves in the fuel line that might be bad or reversed.


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Eric @ TWC Business Class wrote:

I've posted an update under a new subject; not sure if that't the correct thing to do, but it does keep the topic current.
I'd really like to know more about the operation of my motor too, especially how fuel gets into the engine. Could it also be a filter problem?
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Could be. Keeping filters fresh is the #1 most important thing ever secret to a happy diesel.
But a dirty one won't give you intermittantness.
Air leak or no 'lectricity to the plugs is the most common cause.
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Richard Sexton wrote:

I think the plugs etc are ok. In a recent fault condition, there was no black smoke upon eventual starting, which possibly indicates that there was no fuel getting through. Tell me, I'm assuming that there is a small pump (fuel lift pump?) at the top end of a pipe (or tube) that enters the tank at the top and goes to the bottom. If there were an air leak somewhere around the pump, or a hole near the bottom end of the tube, this would probably give the symptoms that I'm seeing. It makes some sense to me, but only if this is what it looks like in reality.
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At LEAST two people have already suggested this - any more wanting to join in ?
Nick
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Nick wrote:

Right, thanks. I counted only one suggestion of an air leak in this thread in this ng. So, is the 'dip tube' part of the pump?
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On Tue, 5 Sep 2006 19:12:56 +0100, "Grumps"

I was just about to jump in and say air-leak.
I had a '94 325 TD, and one of the injectors has a sensor wire (so it costs 130 instead of 35). The seal on the sensor (whatever it does) is a weak point, and when it starts to leak it lets air back into fuel line... When I came to start the car after it's been parked for a bit I had to crank and crank and crank until the air cleared and then it would run fine.
However, I suspect your 530 has a more modern common rail style engine, and not a tractor inspired one like my E36, so I'm now completely out of my depth!
Dodgy.
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