cmyachtie

Have been plagued by cold start misfires that most often do not cause the SES to show but will leave faultcodes eg. PO300, 301, 302, 307 etc. Usually it will be 1-3 cylinders that cause it and sometimes only 1 but always a different one so it seems to be totally random.

This has been the case ever since I got car 4 yrs ago, mostly occurs in winter after cars has not been driven for more that two days and temps are around or below freezing.
Have replaced plugs and initially when they first occurred moved coils around but after this length of time am convinced coils are ok. Have replaced vacuum hoses and those flimsy orange pcv valvesAs wel, got recently concerned that maybe battery was culprit, have OEM AGM battery now 5 yrs old so started measuring voltage, on boosting terminal under hood will be 12.9V, with car asleep after two days, however on my phone app over BT ELM it will read 12.5V, which will then drop to 12.1-2V when car wakes up on boost term will then be 12.4V.
Ther seems to be approx. a .5V drop between the two points. When engaging the starter voltage will spike to 10.something Volts only for the split second starter runs. Since this will be at its lowest during coldest ambient temperature am wondering if my misfires could be caused by this. Usually car will assume normal run after a few seconds and for the worst stumbling during startup I will turn key to off and restart which has sofar always got the engine running smooth.

Also been thinking maybe should be running thicker oil as lube will,drop down and maybe VVT could be involved due to lack of lubricant.?

Any suggestions are welcome and anyone with N62 engine that can monitor their starting/resting voltages for comparison would be welcomed.

Also if any of you with a smartphone diagnostic app like Carly etc. Are willing to do some measurements like I did above for comparisons I would appreciate it,
Thanks

EddieboyS

Had the same issue with my 06 550i. Just replaced the plugs (Bosch) and all 8 ignition coils (Bremi). Purrs like a kitten. Car has ~97k miles at the moment.

FormerE30Owner

Your voltages seem normal. My voltage on start up drops to 10 volts during cranking, which is normal. My 2005 N62 with 285000 kms also experiences what you seem to be experiencing and I suspect weak coils - I have replaced 2 (#1&3)at the 270K mark since they did raise SES codes. The rest are original and I am still experiencing rough initial idle at startup, albeit not as bad as before. Just because you moved the coils around and you didn't see a consistent difference does not mean that the coils are OK. If the coils are weakening than the effect will be intermittent and not show on the SES. Your other comments about the lubricant do not seem relevant to this issue.
Salut, Bob P.

cmyachtie

Thanks for the responses!

Hyper_545i

Search Intermediate Levers. Not sure if the same symptoms you are experiencing or not. Or as mentioned it could be a bad coil(s). At the age of the coils it wouldn't be a bad idea to swap out as preventative maintenance. Couldn't hurt. Are you getting any misses while driving or just idle? A bad coil would misfire on idle as well as during driving.


Good Luck OP! Please keep us updated.

cmyachtie

I have researched the intermediate levers on this but AFAIK it only affects levers outside of my built date, PLUS never had any problem/misfires once engine is warmed up as a matter of fact only for the first few seconds of a cold start usually goes away after a few seconds and rarely have to turn ignition off and restart and all is good again, before I replaced the plugs last year some cyl. we're repeating so I swapped coils and the faults did not move with the coils which makes me reluctant to just throw $ at it with new coils, unless they are all getting bad in tandem due to their age, which I think would be highly unlikely.....
Would love to be corrected if this is the wrong thinking...LOL

FormerE30Owner

Had exactly the same symptoms this morning, just like other colder mornings. I am used to it and not worried. If you start to get misfires under load however, then that is time to question the coils. Those were exactly the symptoms (misfire under load) I had and the misfires were always on the same cylinders (#3, then #1).
I suspect that this has to do with the cold temperature and the richer fuel mixture not always firing correctly on random cylinders. The computer quickly adjusts accordingly and the misfires go away.
Salut, Bob P.

cmyachtie

You know Bob, I think you're right about this my car has done this randomly in cold weather since I got her 4 yrs ago never got worse or been able to find a pattern OT around freezing
temperatures and being parked longer than a day and night in a row. Started recently plugging the battery in on a minder to keep it topped up even that has not made it any better.
Will accept it as being a BMW 545 'feature'......LOL

FormerE30Owner

I have installed a 5 watt solar panel attached to the engine compartment connections, which serves nicely as my battery tender during the day, obviously. Got it from CND Tire, Of course this only works if you leave the car outdoors, which I do, since I don't believe in heated garages in winter! Nothing worse than warm salt water for corrosion of body parts - but then you would know that from living in Halifax Salut, Bob P.