Misfire, tough idle - fuel injector issue?
 

4 months ago, my 2008 3.0si suddenly engine shaking, tough idling right after i started. Engine fault display on the dash board. and it was misfire number 6.
With 90,000+ miles, i replaced all 6 new spark plugs and ignition coil. and replace air filter. The car running perfect until last 2 weeks ago:
Sometimes after i stopped at stop sign/red light, It's shaking and lost power and engine fault appears on the dash board again. And this time misfire number 4!

Sometimes it shaking and misfire, sometimes it went off and back to normal.
I have mix 2 bottles of fuel injector cleaner for each 3/4 tank last 10 days. and the misfire issue is still on and off sometimes.

I am thinking to replace 6 fuel injectors this time.

Any ideas?

Water in the gas? Try a fuel additive that removes water. Change fuel filter. Seems unlikely that your fuel injectors would all be bad. . .

Forget the fuel injector cleaner and the fuel injector problem.

If the misfire is at idle as you mention, more often than not the problem is a vacuum leak. Assuming these are the same 3.0l engines that have been around for a while, you should really read my comments and links in this thread from a different forum - http://forum.e46fanatics.com/showthread.php?p=16727145

There are some differences between the newer 3.0l engines, not sure the CCV system is the same.

Also search as there are problems with some of the rear injectors getting water damage from cowl leaks as well.

Most problems with the M54 and N52 engines with a single cylinder misfire come from the ignition coils. As a matter of fact, in DIS and ISTA test schedules, if there is a misfire always the same instruction pops: "If the engine is equipped with Bremi igntion coils replace all of them" :rofl:

Sorry, HAVE to totally DISAGREE at least with the M54 problems being ignition coils. Yes they can be an issue from time to time, BUT most idle misfire problems are due to LEAN conditions.

The E70 is a bit young and may be a different configuration than the earlier M54 equipped cars to have the rampant vacuum and crankcase air leaks. An OBDII tool to monitor the warm idle Fuel Trim values is a good start for identifying vacuum and crankcase air leaks.

Many of the cold start misfires are also vacuum leaks from heat compressed silicon or rubber gaskets that do not expand like they should when cold.

Lean misfires due to vacuum leaks are not just on BMW's, EVERY manufacturer has this problem starting around year 8. Plastic and rubber that holds vacuum under the hood of a modern vehicle does not survive beyond 8 years on average.

Before you disagree, please read carefully. I wrote "single cylinders misfire" which is much different than multiple cylinders misfire, which is what you get with a lean condition.

Single cylinder misfires are ALSO primarily Lean conditions as well. Not ALL Lean conditions are GLOBAL problems. Additionally soft fuel pumps can also cause single or double cylinder misfires.

Take some time to read what I outlined in the link posted, this primarily pertains to the M54 this is not my first rodeo. The N52 is a different animal, but these engines are now getting to the age where some of the common problems with vacuum leaks may be coming to light now. I am active on many forums and even other German car forums are quick to point the finger at faulty coils.

AGAIN, ignition Voltage demand is lowest at idle, most idle related misfires are not typically secondary ignition problems.

I just get tired of all the "replace coils" and "fuel injector cleaner" as some of the first suggestion when a misfire or driveability problem is mentioned.

When I get a single cylinder misfire i replace the coil immediately, in any BMW engine, and it has done the job in 95% of the cases. that should be roughly 50-60 coils in the last 2-3 years. If you also read carefully the first post you may understand that I am not wrong.

Guess we have to agree to disagree.

The OP replaced all the spark plugs and coils and STILL had a single cylinder misfire but on a different cylinder after the spark plugs and coils were replaced. Doubt his problem is with a new ignition coil.

Warm idle Fuel Trim info would give some insight to how correct the air/fuel mixture is.

I do not let "software" tell me what to do when repairing a car. I use scan tools or software to gather data and then make my own mind up.

If I was paying for a repair and someone replaced ALL the coils, not sure I would be so happy for paying for this.

I rarely replaced coils and if spark plugs are replaced in a decent interval, the coils should not be over stressed.

Well, OP has to clarify if he replaced all spark plugs or just 1. it is not clear from his post and and everyone has interpreted it in it's own way.
Nowadays, if you order a coil from BMW you will receive a product made in China which fails within a few months, at best :yikes: Aftermarket coils also are are made in the next Chinese village, so not a big chance to last for a long time. Either way, still coil for me ;)
The Bremi coils on my previous X5, '03 4.6is, all failed within 1 year/10k miles. I always carry a spare coil and with my luck they all failed far from home so i had to replace 5 of them at different occasions before I replaced the rest in one shot. Of course i installed used Bosch coils and they still work fine after 3 years/30 k miles.