[monkeyboy]

My 328xi 2011 (87K mi) is intermittently throwing P0305 misfire codes again (or similar). The previous times its happened, I changed out the coils and it became happy. This time, a new coil doesn't seem to fix the problem -- perhaps the plug needs changing again (although I thought they are generally good for at least 50K mi) or perhaps the fuel injector?

Anyways my main question is that I don't quite understand how it can misfire (generally with added load) a few times, but otherwise continues to run fine. But under certain rarer conditions (like it misfires for 5-10secs) and then it getting into a state where it continually misfires (and that is when the service light comes on an a P0305 code is registered). The only way out of this state is to stop the engine and restart.

So why can it easily recover from a few misfires, but with slightly more misfires, it cannot "recover". What is special about this constant misfire state? I don't think this is "limp mode" -- no limp mode light comes on and it feels just the same as the occasional misfire, except it is constant...

[phineasxx1]

https://www.e90post.com/forums/showthread.php?t=1818011 read my post bro i got a same problem

[monkeyboy]

Ok, so after I replaced the #5 coil and still got P0305 codes and misfires under load...

I ran through the remaining gas in the tank (octane 87) til nearly empty.
Then I added Techron fuel injector cleaner as some have recommended, and put in 3 gals of octane 93 (total gas in tank probably about 5 gals, averaging octane would be about 91. Then I drove...

It is much better. I can't feel any more misfires, no codes, etc. So what can I conclude?

- Probably the old #5 coil is still good.
- The Techron helped solve the misfiring problem?
- The higher octane helped solve the misfiring problem? But then if it is just the 93/91 gas, why wouldn't other cylinders misfire -- always just #5. I've using 87 gas for years without problems.
- Or is it just that 93/91 gas is just "papering over" a problem that still exists?

I suppose I should at least run out the current tank, then refill with 91 to see if the Techron is the major improvement factor.

But insight as to whether using 91 instead of 87 gas could explain the symptoms would help (only misfiring #5).
Could using higher octane gas cover up a problem with plug #5? (or even coil #5)?

[MightyMouseTech]

First off, why are you putting 87 into it?

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[bluewater328]

Originally Posted by monkeyboy

Ok, so after I replaced the #5 coil and still got P0305 codes and misfires under load...

I ran through the remaining gas in the tank (octane 87) til nearly empty.
Then I added Techron fuel injector cleaner as some have recommended, and put in 3 gals of octane 93 (total gas in tank probably about 5 gals, averaging octane would be about 91. Then I drove...

It is much better. I can't feel any more misfires, no codes, etc. So what can I conclude?

- Probably the old #5 coil is still good.
- The Techron helped solve the misfiring problem?
- The higher octane helped solve the misfiring problem? But then if it is just the 93/91 gas, why wouldn't other cylinders misfire -- always just #5. I've using 87 gas for years without problems.
- Or is it just that 93/91 gas is just "papering over" a problem that still exists?

I suppose I should at least run out the current tank, then refill with 91 to see if the Techron is the major improvement factor.

But insight as to whether using 91 instead of 87 gas could explain the symptoms would help (only misfiring #5).
Could using higher octane gas cover up a problem with plug #5? (or even coil #5)?

The manufacturer recommends 91 octane. I dont think you can call it "covering up" when its literally on the gas lid when you bought the car.

Im sure dirty injectors could contribute as it often does. But not sure why people buy a car that recommends 91 and question why it can't run 87 (good lord man, not even 89) well. The car retards everything for you and tries to compensate, but its not really the spec it was designed for. It isn't ALL marketing when they sell more than 87.

[monkeyboy]

Well it's been running fine for ten years on 87. In fact all three of the series 3s that I've had have ran fine on 87 for the past 25 years. And none of the many mechanics I've used including bmw dealers have ever told me, Gee there's a problem here, are you using 93 gas? So it seems that nobody notices anything wrong or different...

https://www.nytimes.com/2008/08/03/a.../03OCTANE.html

"BMW, for example, recommends that all the cars it sells in the United States use premium fuel, but they will run on regular.

“There generally isn’t any harm done to the engine by using lower-octane fuel,” said a BMW spokesman, Thomas Plucinsky. “Because our engines do have very good forms of knock sensing and are able to deal with lower-octane fuels, you will not have any drivability issues. You will, however, lose some of the performance.”"

[hassmaschine]

It's optimized for premium - it can run on lower octane, yes, but jesus. why buy a BMW if you're just going to put shitty fuel in it?

Probably it's not the 87 octane directly, but it's going to be running on the edge of "safety". So now it can't compensate anymore and it's misfiring.

the N52 has a compression ratio of 10.7:1, and yes, that's really pushing it for regular fuel. If you were driving an E30 325i back in the 90s, that had a compression ratio of 8.8:1...

[MightyMouseTech]

Originally Posted by monkeyboy

Well it's been running fine for ten years on 87. In fact all three of the series 3s that I've had have ran fine on 87 for the past 25 years. And none of the many mechanics I've used including bmw dealers have ever told me, Gee there's a problem here, are you using 93 gas? So it seems that nobody notices anything wrong or different...

https://www.nytimes.com/2008/08/03/a.../03OCTANE.html

"BMW, for example, recommends that all the cars it sells in the United States use premium fuel, but they will run on regular.

“There generally isn’t any harm done to the engine by using lower-octane fuel,” said a BMW spokesman, Thomas Plucinsky. “Because our engines do have very good forms of knock sensing and are able to deal with lower-octane fuels, you will not have any drivability issues. You will, however, lose some of the performance.”"

Well, I am a dealer tech, and I am telling you to stop that.

[monkeyboy]

ok well, I really wasn't intending to start yet another discussion about octane and BMW's, unless you're specifically suggesting that low octane, rather than any other factor (fuel injectors, coils, plugs, etc) is what has been responsible for causing my cylinder #5 to misfire now (but not before).

Is that the suggestion/hypothesis given the available data/observations?

[hassmaschine]

I'm not saying it's directly responsible. But your car is no longer new - and 87 octane *barely* works with the factory tune, because while it can adapt, the stock compression ratio is nearly 11:1. That would have been considered race-engine specs not that long ago.

After a lot of time and mileage, things have started to wear. Carbon has built up in your cylinders, increasing the compression ratio a little (and causing hot spots or areas where fuel doesn't burn efficiently). So now it can't run on the knife's edge of adaptations anymore.

I mean, you've replaced the obvious parts, but that didn't work - and running proper fuel fixed the issue. Seems self explanatory to me.

[monkeyboy]

Ok, so I ran the quarter tank of 91 + Techron to near empty. No more misfires.

Then I filled the tank up with 87 gas -- still no misfires. It now seems fine. I decided to add another bottle of Techron just for good measure (its much more diluted now).

So... conclude that Techron really worked? Fuel injectors or something else along the fuel pathway was causing the misfires on #5 and Techron cleaned it up?

I will say that, perhaps its my imagination, but the engine did seem to "purr" a bit better with 91...

[mapleleaf1773]

In my experience, higher octane has better detergents that help keep the carbon build up to a minimum. I use it, no one wants to replace expensive fuel injectors.

Another story - I would get a slight misfire on cylinder 1 and a p0420 cat code. After a bottle of cataclean and 2 bottles injector cleaner (over 5 tanks of gas) the misfire went away except at cold startup. Still not perfect.

I then realized the previous owner didn't "register" the battery. I checked the date and it was almost 4 years old. So i replaced the battery, registered it and no misfire, no p0420 code no running issues remain even at cold start. I think the old non-registered low battery was definitely contributing to those issues.

Just an experience i had, thought I'd share

[E92_William]

I had very good luck with Techron sorting out my old 335s endless n54 injector gremlins. Probably a temporary solution and a sign to get the injectors properly cleaned but at least it works now. If you think it drives better with 91, try 93! I only run 93 in my BMWs, sometimes my brother wants to be a cheapskate and put 87 in the e46 but he knows better because I'll notice right up.