What are the consequences of an amateur engine replacement in a BMW and how to fix it?

BMW driver question

I am after an engine swap from a BMW E36 to a BMW E46. There is a small problem with the electrical system and I don’t really know how to connect the cables to make it all work. The swap was supposedly done by mechanics and they made a horrible mess in the engine connection box to the car.

These great mechanics connected the cables, but not everything works as it should. The engine fires up and then the suction comes on. Whether it’s cold or warm, the suction comes on. The other thing is that the clocks practically don’t go at all – the temperature shows all the time at maximum, the fuel gauge shows differently, and the other clocks don’t even vibrate. How to fix all this?

The question is about the BMW 3 E46. The following advice applies to all BMW combustion cars.

BMW 3 E36 | By OSX (Own work) [Public domain], via Wikimedia Commons

Response from BM Cars service

The described problem is typical of amateur vehicle modifications and does not apply only to the BMW brand. When deciding on such a serious operation as changing the engine to something other than the factory engine, you need to be aware of the consequences of such a change. It is not only about the moment of firing up the engine, but also further operation.

The topic of engine replacement and repair is described in more detail in the services section.

If your service center undertook such a service and received payment for it, then by law it is covered by the warranty. We suggest you turn to the service where the engine was replaced with a warranty claim. The described defects – must not occur and should be removed.

Possible repair in the next service is to incur additional costs associated with checking the engine harness and electrical system and verification of the work already done. This will be payment for work already done and paid for.

You are welcome to use our service.

BMW engine replacement in the works

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BMW 318i E46 | By Alexander Lindquist[CC BY-ND 2.0]