525 TDS difficult to start

And the BMW 325 TD/TDS. It's known as the M51 engine.

Diesel isn't leaking out (well not much, see below), air's leaking in and the diesel is running back down from the filer housing under gravity as air is sucked in.

This is exactly what happened to my 325TD a couple of months ago.

You are quite correct, the air bubble is your problem, you're having to crank the engine, pumping the air through the injector pump until eventually some fuel gets there and it fires up.

The BMW dealer is talking out of his backside. I'd go find another one if he can't see that as a fault. Not only should diesel fuel systems not have air in them, but this is a classic sympton of a well known BMW fault.

Things to check...

1) Bleed back pipes. At that age the bleedback pipes will have long since given up being rubber, and will now be as flexible as concrete. The split, they let air back into the system. Easy DIY fix, buy 4 feet of 2mm bore cloth braided fuel pipe from your local car parts store, and get to work with a stanley knife.

Take the plastic trim off the top of the engine and you'll see the little back pipes linking everything together.

You won't be able to just pull them off as they'll snap and leave their ends on the enjectors. Best technique is the run a stanley along the side on the last inch, which will get it to release, then pull them off... But have a pair of needle end pliers to hand to fish off the ends just in case!

Job done for a couple of quid...

2) Unfortunately that wasn't the cause in my case, but it's always a good idea to change those pipes for the couple of quid it'll cost.

Here's the well know, cause...

Once you've got the plastic trim off the top of the engine, have a look round the 4th Injector back, I bet you it will be moist with diesel, and all the others dry. Now look more cosely round that injector, and you'll see it actually has a wire coming out of it, unlike the other 5. Say hello the the master injector. Also say hello to a design flaw. The sealant used where the wire comes from the inside of the injector, breaks down over time and leaks. Air gets back down the injector pipe as the car sits there.

Another job that can be done at home, but you will need a special long reach socket with a hole in the side to feed the wire through, to get the injector out. A good accessory shop will have one, it's not a BMW only thing. You'll also need a bit of luck and a long screw driver to release the plug from the socket slightly lower down the side of the block.

Now the bad news. All the injecors cost about £30-40 each... except one... One costs £140. I'll let you guess which one.

Good luck,

Dodgy.

Hi,

Thanks a lot for the reply - I did change the glow plugs about 3 weeks ago, had the manifold off to do it and noticed these pipes were a bit manky / perished, but didn't know what they did so I left them pretty much alone...

However I had to move them out of the way to assist in the removal / replacing the glow plugs so I am sure I would not have helped their "sealing"... I am wondering why the garage I have the car at has not jumped on this one .... they are specialists in older BMWs and do seem to know their stuff.....

I hope to hear from the garage tomorrow and if they are still "floundering" I will try to retrieve the car and do it myself, if they haven't got the diesel injector pump off (eeeek) or the car in bits...

Thanks again for the info - if nothing else I will replace those little "loop through" hoses you mentioned first.....

............. and I'll let you know how I get on.

Nick

Oh they'll be sealed onto the injector alright, they bake on! That's why removing them is so much fun, but they become brittle and crack, especially when someone's pushing them about to get the manifold nuts. :-) As for the garage being a BMW specialist, that they might be, but I expect 95% of their customers have petrol BMW's. Diesel is a completely different beast and has it's own set of tricks/problems. You'd be better off talking to a diesel specialist when it comes to engine problems.

Air in the fuel line isn't a problem on petrol injection or the very modern common rail diesel, as the fuel pumps round and the air bubble just gets pushed past and back to the tank down the fuel return pipe.

However a mechanical injector pump diesel engine like yours, mine and a million London taxis, doesn't have a fuel pump with a return pipe to shift the air, it has an injector pump that can only take it and pump it through the injectors as you crank the engine over. Any air in there is a bad sign and certainly not normal.

Nooooo! Step away from the injector pump! If I were you I'd phone them first thing or you'll end up with labour costs more than the cars worth at this rate!

Best of luck, but I do have a nasty feeling it's going to be that injector.

When mine started doing this in July I took it to a diesel injector specialist I know, and asked one of the engineers if I could pick his brain for a second. He came outside and told me what it was before he'd even turned his torch on. He said I was the second 2.5 diesel BMW that week and that they're really well known for it.

Hopefully you will be really lucky, and it will be the bleed back pipes complaining following the distrubance of the manifold coming off.

Isn't glow plug changing such fun, did it myself 2 weeks ago... Did you end up spending most of your time trying to remove the baked on remains of the gasket from the head?

Good luck.

Dodgy.

So what do these bleed pipes do - there does seem to be a return to the tank pipe...

and only had to use two or three as they came away quite easily - I did have to persuade the remnants of two off though with a sharp edged piece of hardwood but not too bad - I guess a bad joint would only bleed away a bit of pressurised air, unlike on a normally aspirated petrol engine where mixture would be messed up as well, potentially

Thanks again.

Nick

It is a return pipe, but unlike a petrol car they are after the injector, they're kind of like an overflow. On a petrol or common rail diesel injection, the fuel is electrically pumped round past the back of the injectors on a big loop.

A petrol injection car's fuel pump pumps more fuel than it needs, and pumps even without the engine running, a mechanic diesel injector pump only pumps what it needs, and only with the engine turning. The injector pump is driven by the engine. The only way to clear the air is to crank the engine and pump it through the injectors, squirt by squirt.

I wish I could draw a picture, then it might make sense!

persuade the remnants of two

joint would only bleed away a bit of pressurised air, unlike on a normally aspirated petrol engine where mixture would be messed up as well, potentially

You lucky lucky man.

I forgot to stock up on gaskets, so every single one of them welded itself on and got torn apart when I pulled off the manifold. I spent a good 30 mins clearing them all off with a scraper... Then another half hour cutting more gaskets. I knew I had that sheet of gasket material sitting in my garage for a reason :-)

But as you rightly say, all it would do is hiss air and loose boost and not break anything.

And now, having just gone out to my car for something, I find the drivers door central locking isn't working any more, the alarm opens and shuts all the doors except the drivers... Guess I know what I'm doing tomorrow! (Next week Dodgy will be an authority on removing door panels!)

Dodgy.

Well, I phoned them at 08-00 hrs today and they had already been checking it out - they applied vacuum to as couple of pipes and sucked until all the air was purged out of the system yesterday - it started immediately after re-assembling everything and again this morning - they are quite sure this "did something" as they were unable to see any air in the system again and it always started first time - so I collected the car mid-morning and it seems to be fine - I think they were feeling a little guilty - they didn't charge me anything and must have spent some 5 to 10 hours on it this week.... so either that or they did re-instate something that perhaps they didn't previously ! I will probably never know. - Anyway I am just going to look at the plastic pipe whilst I start it after a 5 hour sit on the drive and see what happens.... and if I see a bubble... If it is there, I will firstly do the injector loops (although they said they had done that a month back) and if all OK there it will possibly be the " no. 4 injector job " you suggested at some point... Just started whilst looking at that plastic pipe - there was a tiny airbubble in it at the highest point (size of a pin head) and it hardly moved as I turned on the ignition - it started immediately.... however as it was idling and I was just looking around, the injector pump end of this transparent pipe from the fuel filter was definitely weeping - about a drip every 10 seconds ! On moving the pipe slightly the leak became worse... so it seems this pipe is cracked ! I can't think it is more than a few pounds so I will replace that on Monday ! Coincidence perhaps but its right in the area of the problem ! I don't think its quite over yet but hopefully nearly and not too expensive ! Nick

You lucky lucky lucky s*d!

If that feed pipe from injector pump to filter is leaking it could be the source of all your troubles. Don't think much of your garage for not spotting that!

Dodgy.

Hello again..

Yesterday I stumbled upon a significant-to-the-problem discovery whilst pondering things with the bonnet up and engine running..... Whilst prodding and poking around the fuel system generally, I was wiggling the pipe from the fuel filter to the injector pump, the translucent plastic one about 12 inches long and I saw a wetness develop at the union to the injector pump. Further detailed investigation revealed that the plastic pipe had split nearly all round the union at almost the very top end of the metal that it was "heatshrunk" over - I immediately ordered a new pipe and left the car at home today. I returned after work with the new pipe and replaced it - the old pipe was hanging on by a thread to the union - it must have been leaking under pressure and I am sure it would have been leaking air back in under vacuum or engine off state.....

I am confident that this was a significant factor to my problem - the crack was not "new - it had some considerable time's worth of accumulated muck in it and was probably leaking more or less depending on the weather etc....

I am disappointed that the garage's tests and investigations did not find this, albeit obscure, problem - I wonder if the fuel pump was indeed necessary.... but glad / hopeful it was not the injector pump / injectors at fault...

Nick

On Tue, 11 Oct 2005 21:32:27 GMT, "Nick" waffled on about something:

You lucky b*gger!

Glad to hear it though... Nice to have a cheap and happy ending once in a while!

Dodgy.

Had a very similar problem with my 525TDS - garage changed lift pump and no joy. Not sure if yours is the same, but mine was more difficult to start if it was pointing up-hill!

Anyway, in the end garage found it was a leaking injector and I had to crank it for ages (like yours - time dependent with how long it had been last used) until enough fuel pressure built up to start the engine.

Changed appropriate injector and it was absolutely fine. Independent BMW specialist found the real fault in the end, main dealer was useless, and no clue at all.

Matt.

Nick wrote: