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PostPosted: Sun Aug 30, 2015 7:42 am 
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Joined: Wed Sep 15, 2004 2:24 pm
Posts: 411
Location: North Brunswick
Our 540iT has developed an occasional misfire at speed. New plugs helped, but did not cured the problem. I'm suspecting a coil is going bad. But it's not bad enough to set the SES so my Peake Reader is no help in identifying which coil(s). Replacing all 8 is an expensive proposition unless the ones for $10 from eBay/Amazon are really any good (boot included!). Does anyone have a better reader/analyzer that I can plug into that displays the misfire counters so I can narrow it down? In the vicinity of Central Jersey would be most helpful. Thanks!!

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-Keith

'11 335D & '17 340GT


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PostPosted: Sun Aug 30, 2015 8:10 pm 
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Joined: Wed Feb 23, 2005 1:32 pm
Posts: 472
Location: Green Brook,NJ
Keith,
Even with more expensive code readers or factory diag equipment, it can be very difficult narrow down a intermittent misfire. Ebay coils sort of would scare me to use in long term ,not saying they are all junk but just beware. My suggestion is to buy 1 or 2 coils and just move them around from cylinder to cylinder. keep track of what you pulled out until you find the source.
of course with the above being said that there is actually a coil issue.

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Ray
2018 M3 ZCP
2018 Shelby GT350


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PostPosted: Mon Aug 31, 2015 8:30 am 
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Joined: Wed Nov 10, 2004 1:37 pm
Posts: 643
I second Ray's advice, and suggest you bite tbe bullet and spring for an OE coil.

If you succeed in getting access to a scanner capable of displaying BMW's smooth-running values, you will have to have an assistant view them while the misfire occurs, as my observations are that the values will return to normal [near zero] when the misfire goes away.


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PostPosted: Mon Aug 31, 2015 8:35 am 
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Joined: Wed Sep 15, 2004 2:24 pm
Posts: 411
Location: North Brunswick
Thanks Ray & Vic. Guess I'll purchase 2 real Bremi coils and start moving them around. The pain in the neck part is having to remove the HVAC filter and snorkel on the E39 to get the cover off to the coils.

Hopefully my scientific analysis that it's a coil is correct. The new plugs helping a lot makes sense as with a smaller gap they require less voltage to fire (they had 60K on them, but the previous set made it to 100K with no issues). A little on-line research indicates the leaner the mixture, the higher the firing voltage. It's during highway cruising (leanest mixture) that the misfire occurs. Get into the throttle a little and it immediately goes away (richer mixture). My hypothesis is when the firing voltage gets high enough the spark is occurring inside the failing coil and never makes it to the plug.

Based on visual only it appears 2 of the coils were replace at one point (they have a black label instead of white) and the other 6 are originals from 2000.

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'11 335D & '17 340GT


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