Compression Test: How to Check & Diagnose

Question:
Can the compression be measured through the glow plug bore in a common rail system? (Values around 15 bar were measured.)

Hello.

I can't really think of any reason why it shouldn't work with a common rail system. The only thing you have to prevent is fuel from being injected during the compression test, otherwise the pressure accumulator will most likely break.
"15 bar is simply too low for a diesel engine. Did you measure this value on multiple cylinders, or just one?"
Are you sure that no bypass valve or similar device prevented the correct airflow to the engine during the test?

Best regards, Rainer.

Set the values for all four cylinders to 15 bar.
Intake system was clear. I can't find any explanation. The engine starts, but runs a bit rough, and even reaches its maximum speed.
Could pressure potentially leak out through the electric nozzles/seals during the pressure test?

Hello,

Hansi wrote:

...Could pressure possibly leak out through the electric nozzles/seals during the pressure test?

Not really...

Does the compression pressure tester work correctly, and is its check valve located as close as possible to the glow plug opening on the combustion chamber side of the cylinder head?
The volume between the glow plug opening in the combustion chamber and the check valve of the tester must be as small as possible.

Best regards, Rainer.

Hi,

15 bar is definitely not enough!!

The old VK diesel engine from Volkswagen had a pressure of 28 ± 2 bar, with a wear limit of 26 bar.

I estimate that the turbo-diesel engines with TDI or common rail technology should have a pressure around 25 bar.