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BMW 328Ci DTC 242 (P0305)

Q. Hello Sir, I just got my hands on a 2000 BMW 328Ci, nice car, 2.8 liter 6 cylinder. Manual transmission with 85,000 kilometers. My check engine light came on so we scanned it, ignition coil #5 was misfiring so we replaced ignition coil #5 with ignition coil #1. Switched it's position just to double check that it's the coil. I also changed the spark plugs on it.

BMW 328Ci DTC 242 (P0305)

But the light was ON prior to me changing the spark plugs. Two days later check engine light comes on again, so we scanned it again. Guess what? Ignition coil #5 again!! So it's not the ignition coil!! I Use high octane fuel!!!

When I first start my car in the morning when it's cold, it starts idling at about 1,000 rpm and then it drops gradually till about 700 RPM in about 1 minute. But as soon as it gets to 700 RPM it starts idling rough between 500 RPM and 700 RPM for about a ½ hour.

Somebody told me to check the boot where the ignition coil sits and close to the spark plug because condensation gets in there if the rubber boot is torn or damaged!! Can you offer any suggestions!!

The DTC # is 242 which is misfire #5, and after I switched the ignition coil from #5 to #1 cylinder to check the coil. Two days later check engine light came on again. So when I scanned it the code is still # 242 ??????!!!!!!!!! If it was the ignition coil then #238 should have came on. Right?

I'll appreciate your help,
Thanks in advance

A. According to my BMW manual, DTC 242 (P0305) is "Misfire, cylinder 5". There are two things that can cause a misfire in a particular cylinder, bad secondary ignition component or a clogged or bad injector. DTC 242 does not, specifically, point to a bad coil or injector. It just says there is a misfire in cylinder #5 and it's up to us to determine the cause.

By swapping ignition coil #5 with ignition coil #1, and coming up with the same code, you have proved the ignition coil is not the problem. If it were the ignition coil you are correct in that you would now get a DTC 238 (P0301).

So now we have narrowed it down to the ignition boots and injector. For $11.50 I would get a set of boots from the dealer and replace them. That will, definitely, eliminate a bad boot as the problem. That would leave just the injector.

To check the injector you can get a "Noid Light" at a parts store. Unplug the injector connector and plug the niod light into the injector connector. Start the engine. If it flashes while the engine is running, then the injector electrical system is working. If it stays on steady, you have an open in the wire between the injector and the PCM or a bad PCM.

BMW 328Ci DTC 242 (P0305)

If the light does not come on, you have an open in the wire on the power feed side of the injector. You can jump power from one injector to another to see if it starts working. If it does you have a definite problem on the power side of the injector.

Additional Information provided courtesy of AllDATA

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