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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > Mechanical Maintenance and TSBs: Break-in / Oil & Fluids / Servicing / TSBs and Service Bulletin > Help with Compression Test? - F30 N20/N26
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      12-13-2018, 07:21 PM   #1
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Help with Compression Test? - F30 N20/N26

Hi all,

I have been searching Google and threads on here all day and have not found a definitive answer on how to properly perform a compression test...

Model: 2014 F30 328i - SULEV N26

I have a pretty decent idea of how to do it, but I am not certain on which (or if all 4) fuel fuses needs to be pulled.

Fuel related fuses listed on diagram: 149, 150, 151, 165

Here are the steps I know so far:

1. Remove fuel pump fuse

2. Crank the engine so no more fuel is being delivered and it stalls out

3. Disconnect all ignition coils electrical connectors

4. Remove the coil and spark plug from the cylinder I will be testing, insert Compression Gauge

5. Crank engine 5 times

6. Assemble spark plug with coil, move on to next cylinder?

Is there anything I am missing or tips/tricks to make this easier?

Thanks in advance!
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      01-01-2019, 03:15 PM   #2

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That will give you a pressure reading to compare across cylinders and compare to book values. Mechanics used to test the pressure "dry" and then "wet" by squirting a little oil into the cylinder and pressure test again. Any significant change would indicate major piston ring wear.
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