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Discussion Starter #1
Hi,

I have had a 2003 745i for about 4 weeks now and have noticed a lumpy idle when cold which over the last week or so has got worse.
Now, even when the engine has warmed up, there is still an intermittent misfire.
I also get the engine warning light illuminated and the warning not to accelerate too hard.
I changed all of the spark plugs and saw no improvement at all. The next thing I was going to try is the coil packs, but before I do I wanted to know if there was anything else I could check first.
Sometimes the engine idles perfectly (usually only when warm), do coil packs fail in this way ie. sometimes work perfectly ?

Thanks
 

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Hi Rambox11,

One of the more technical gurus will have to answer this for you - I had a similar problem and it turned out to be a dirty/defective MAF sensor. So i caution you about replacing too many costly components before you get the right advice.

Kind regards,

Stephen
 

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yeah they can break down and become intermitant.
is there anyway you could get somone to plug into it to find out what one is the problem?
you dont want to be replacing them all as i reckon they will be expendsive
 

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Discussion Starter #4
Thanks for the replies.

I have a cheap diagnostics cable and some software I got from Ebay.
I cleared the error memory yesterday and have just dumped the error memory today.
I have attached a PDF file with some results. Does this give anyone a clue ?
The Cylinder 5 error seems to be a recurring error.

Thanks
 

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Discussion Starter #5
I have some more information, don't know if its related.
I just took it for a run, all warmed up and idling prefectly. I then removed the dipstick while idling and the engine stalled after sucking in air through the dipstick hole. I put it back in, restarted and removed it slowly, the engine was able to maintain idle now but is constantly sucking in air. I slowly removed the oil filler cap and that sucks in air also.

Any ideas ?

Thanks
 

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Discussion Starter #6
More... I swapped the coil pack on cylinder 5 with another one, cleared the errors and it still reports cylinder 5 misfire
 

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Is that not supposed to be something to do with the Crankcase Ventilation Valve failing (the CCV)? I'm a bit out of my depth though - you will have the N62 engine I suppose - I'm not sure if it is an issue on that engine.
 

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sorry for not being much help, its hard to tell when your not there, but as the above said it could be an air leak? can you hear or see any split pipes?
and also going back to basics, have you checked compresion on cylinder 5? i know its something you probably dont want to think about but its a possability.
 

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Hi Rambox11,

One of the more technical gurus will have to answer this for you - I had a similar problem and it turned out to be a dirty/defective MAF sensor. So i caution you about replacing too many costly components before you get the right advice.

Kind regards,

Stephen
Totally agree. Had a similar misfire fault on mine. Sorted it out myself after my indie had been faffing around for a couple of hundred quid. Got a non OEM air flow meter of eBay and fitted myself. £50 and half an
hour fitting. Problem solved.

With regards to your crankcase air suction problem, the crankcase breather valves could well be the problem here. A refurb of these by BMW dealer set me back a merely £30. Money well spent as they topped up the engine oil,
gave it a valet and did an overall health check :thumbsup

Dont go buy coil packs and all sorts of other expensive stuff till you've tried this. And don't forget. Despite computers and all sorts of other gizmo's, it's only a car with a combustion engine, thus good old fashioned trouble shooting
still applies.

Mine came up with all sorts of faults of misfire codes, and never the same twice.

Good luck
 

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My 745i also had a slight misfire and i just changed the 2 CCV's.Also noticed the little hose that connects to the air intake tube had broke off so i re-attched it and the engine runs super smooth.Both my CCV's were in very poor condition.

Regards
 

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Totally agree. Had a similar misfire fault on mine. Sorted it out myself after my indie had been faffing around for a couple of hundred quid. Got a non OEM air flow meter of eBay and fitted myself. £50 and half an
hour fitting. Problem solved.

With regards to your crankcase air suction problem, the crankcase breather valves could well be the problem here. A refurb of these by BMW dealer set me back a merely £30. Money well spent as they topped up the engine oil,
gave it a valet and did an overall health check :thumbsup

Dont go buy coil packs and all sorts of other expensive stuff till you've tried this. And don't forget. Despite computers and all sorts of other gizmo's, it's only a car with a combustion engine, thus good old fashioned trouble shooting
still applies.

Mine came up with all sorts of faults of misfire codes, and never the same twice.

Good luck
+1
it's easy to forget going back to basics somtimes.
trouble is there is always alot to check on modern engines that could be the problem.
 

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Discussion Starter #12
Thanks for the replies.

CCV diaphragms are in good condition.
Put a new injector on cylinder 5, no change.
Still got the same problem, still getting worse, consistently misfires under load now, very rough idle when cold, quite smooth when warmed up but still misfiring I think - hard to tell.

going to get a compression test done next week at a local garage.

I'll post the results.
 

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Discussion Starter #14
fixed (sort of)

Paid for head removal, clean and valve re-seating and refit. Misfire still present !

As a last resort, i tried pulling off wires to sensors and when I pulled off the cam position sensor connector on bank 2 the misfire disappeared !
I did try replacing the sensor but the misfire came back.
It's running perfectly now with the sensor disconnected.

I've spent £2500 on this now and I could have just pulled a connector off. Oh well, at least it's running well now.
 
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