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bmw specialist repair & maintenance

BMW M235i Misfiring

When you own a high performance car like the BMW M235i, you are a clear car enthusiast and no doubt make sure you maintain the car’s integrity.  Making sure it looks great, has the best tyres, and a quality multimedia system.  But what about the internal parts?  Do you make conscious decisions about what products you use when things need replacing?

This is what recently happened with a client.  The Newbury based customer brought the BMW M235i to us after the engine began intermittently misfiring.  The problem was mostly when the vehicle was under load, but it was unpredictable.

The client advised that they had already replaced the spark plugs, ignition coils and injectors but still nothing was working. The BMW Engine Management Light was on, there was no power on the engine.  Much to the client’s dismay.

Let’s start with error codes

Error codes within any car are there to guide the technicians, they highlight the problem within the complex engine system.  The BMW error codes present on this M235i were:

  • P0300 – Random Multiple Misfire
  • P0304 – Misfire Cylinder 4
  • P0306 – Misfire Cylinder 6

With the car now in the hands of our expert BMW technicians, they got to work on a full diagnosis.

The BMW was test driven under various conditions, to try and understand the intermittent nature of the misfiring.  The car was driven from start up when it was cold, driven for a while and then also driven under load.  Definitely no power within the engine, and that isn’t what you want or expect from an M235i.

Now, our BMW technician wanted to check the mechanical integrity of the vehicle as it is an unusual fault to have, especially when the client has already told us that they had replaced some of the parts.  Using  PicoScope software, a relative compression test was completed, along with a primary and secondary test of the ignition.

The Pico Scope provided data advising that there was definite intermittent turbulence in the ignition of the BMW M235i, but it also showed that there was no pattern to the turbulence.   Having access to the PicoScope Software, Oscilloscope and the experience and knowledge of our BMW technicians, is key to being able to try and resolve the issue as soon as possible.

Our BMW technician now checked the parts that were replaced by the client, checking the quality of what had been fitted.  With a little research and going over the dealer technical information, we found a known issue with non-genuine spark plugs.

The claims are that the genuine sparks plugs are the only ones that can provide the quality and precision needed for the high performance nature of a BMW M235i engine.

So now having now found this known problem, we changed and re-tested with the PicoScope and waveforms now confirmed that the new genuine spark plugs stopped the intermittent misfiring and turbulent readings.  The Engine Management Light went out and we were no longer getting Error Codes.

It’s all about quality

Quality is key.

So don’t compromise.

The interior, mechanical integrity is just as, if not, more important than the way the car looks.  No point having a performance car like the BMW M235i sitting on your drive looking great, but drives horribly.

Our BMW technician explained the reasons for the error codes and lack of power to the client and the spark plugs were replaced with the genuine, original models.  Being able to complete the tests, and re tests, quickly and with the diagnostic data to refer back to, means that we were able to get the vehicle back to the client and back on the road on the same day as the diagnostic appointment.

We were able to pinpoint the issue down to something as simple as the quality of spark plugs used means that we saved the client a lot of time and money by not having to complete engine rebuild work.  

The Engine Management System was reset and the client advised – they were extremely happy with the level of knowledge displayed by our BMW experts.  It’s about enjoying the high performance nature of the BMW M235i, not feeling let down and out of pocket.

At Fergies, we are proud to be known as German Vehicle Specialists and build that reputation as the garage to take your BMW in the Thatcham and Newbury area.   If you have any questions or would like to book in for a diagnostic appointment, please contact us where one of our expert technicians will be ready to help you.

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