06 X5 3.0 Code PO302 PO303 PO 305 and PO300 Misfire

[FREE100KSECRET]

Originally Posted by crystalworks

Much appreciated. Most of us here don't go by "P" codes anymore but use the more specific BMW codes that more capable code readers pull out of the modules.

Thanks, I only wish I had more specific BMW code reader. Bought the IMPA disc, but have yet to find an old XP laptop to install it on. Live and learn, will be more specific in the future.

[FREE100KSECRET]

Originally Posted by X5chemist

An experienced mechanic knows those code by heart.
Did you pull the plug? I've seen individual plugs fail. You can move the coil pack to another location or ohm it with a voltmeter. Compare ohm reading between coil packs. You can do the same for fuel injectors. One cylinder miss fire will cause other cylinders to misfire even though other cylinders may be okay. The P0303 is where I would look the most for troubleshooting. MAF and air intake leaks are very common causes.

Thanks, have owned a dozen BMW's over the years, and I went by the misfire injector open issue, so ordered an injector seeing that it was specific code, but I will double check coil anyhow while I check further. Given one cylinder misfire can impact others, will check the original #3 injector and replace, but while I have fuel rail off, will check the other injectors to see what the readings are. So thanks again, never had this issue in all the years working on these BMW's.

[crystalworks]

Originally Posted by X5chemist

An experienced mechanic knows those code by heart.

I absolutely agree any pro mechanic working on many brands would.should know them by heart. My exception those who, like me (and probably many of any BMW forums members) who are not pros, only work on BMWs, and were forced to buy a BMW specific tool a long time ago. So P codes haven't been seen in a LONG time (at least 10 years and as many BMWs in my case).

Sorry OP for the slight OT. But your misfire situation is definitely one all of us have gone through at some point on a BMW. It's usually vacuum related but at times can be ignition system (least probably in my experience is fuel supply). If you have access, your short term and long term fuel trim data would be helpful with diagnose by some of the more technically minded members.

When I have misfires, especially at certain mileages, I tend to take the shotgun approach to it and replace all coils/plugs, vacuum lines, crank case breather components, valve cover gaskets, etc, etc. It usually costs more (sometimes a lot more) but saves time on diagnosis and "resets" the clock for another ~100k miles before I'll need to worry about misfires again.

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Thanks, I will start checking for the issue, just thought someone would have had exact same issue, not just random misfires, but specific 2.33 and 4 injector circuits. Will check further and post results.

[cn90]

Multiple misfire codes:

- Air leak, check again and again.

- Bad ignition coil, but usually just 1-2 bad coils.

- Spark Plugs getting old...

- Bad gasoline (contaminated with water).

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Originally Posted by cn90

Multiple misfire codes:

- Air leak, check again and again.

- Bad ignition coil, but usually just 1-2 bad coils.

- Spark Plugs getting old...

- Bad gasoline (contaminated with water).

Thanks, thought about gas as a friend just had that issue given so much rain in area, gas station tanks may have been leaking in water. Put Heet in tank just in case, not change. Engine will start, but will not accelerate normally, so with 4 cylinders suddenly throwing codes, and it was running great, I am stumped. Checked for vacuum leaks, intake manifold ports sprayed with starter fluid to see if any change. No luck, problem started with just #3 with open injector circuit and misfire and only occasionally, so I put in injector cleaner in tank and it was fine for another 500 miles or so, and now 4 cylinders have same codes, so any ideas what could cause this, I checked for shorts in wire harness injectors from DME, no change.

[ahlem]

Also check your compression across all cylinders. I had engine misfire codes and the cause was a bad head gasket.

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Originally Posted by ahlem

Also check your compression across all cylinders. I had engine misfire codes and the cause was a bad head gasket.

Thanks, I will check compression, but given engine ran so strong with no issues, great performance, MPG great, no indication of typical compression issues, but I will check it out, thanks.

[oldskewel]

Originally Posted by FREE100KSECRET

Curious, I had first a PO303 code and PO300 which was occasional, put fuel injector cleaner and it seemed to help, but came back, and no same codes on 2.3.4 cylinder, So what would cause this suddenly, checked connections and harnesses, ordered injector when #3 acted up, but I feel it is something else. Any ideas?
Thanks,

First off, the codes you're seeing probably have zeros where you are typing the letter "O." The letter O is wrong. The zero is right. So when you google it, if you use the letter O, you'll be finding "answers" from someone who at the least made that mistake, and may be making others as well. Google with the digit zero, and you'll be starting from a better place.

So google for P0302, not PO302. And sure, you might find anecdotal info about someone who had a particular component failure, it gave a P0302 code, they read it and posted it as PO302, and before you know it, it becomes internet fact that a PO302 means that particular component is bad. But like most internet facts, that would be wrong.

My understanding from cars in general (including BMWs), is that a P030# code indicates a misfire on cylinder number #. Simple as that. P0300 is a general misfire code meaning that one or more cylinders is misfiring. A bunch of the comments so far in this thread saying otherwise do directly contradict what I'm saying here.

The misfire codes themselves do not attempt to tell you what is causing the misfires, just that misfires are occurring. More specifically, misfires are typically detected by measuring the timing of the crankshaft rotation very accurately (for misfire detection purposes). The CPS or crankshaft position sensor does this.

If a misfire occurs, the piston will not see as much combustion pressure as it should, so the torque on the crankshaft will be a little less, so the time for crank rotation through that cylinder's angle will be a little longer, which the CPS will measure. If that is found to happen reliably enough, the ECU will declare a misfire on a particular cylinder, maybe turn on the Service Engine Soon light, set codes, go to a limp mode, etc.

At that point, you may be on your own to find what is causing the misfire(s) - there may or may not be other codes to guide you (e.g., a lean mixture code). Another complicating factor is that the detection is sometimes not accurate about isolating which cylinder is bad. Accuracy seems to vary with engine types - I'm not sure how accurate it is on these M54s. So you can have a single cylinder problem (for example a flaky ignition coil on #2) that may result in crank rotation speed variations that will cause misfire codes on multiple cylinders, even though the actual problem is only on that #2. So if your problem started with a single P030# code, and now you have a few of them, it could just be that your one isolated problem has become worse rather than that it is spreading.

This is all general stuff. Sorry, I have no "answer" for you.

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Thanks, could be a zero and not the letter, I can't see the difference on my scanner, but the problem is the random misfires and injection circuit open is the problem.