Mercedes A200 2.1 Engine issues

[neal1980]

The initial message was deleted from this topic on 10 March 2026 at 18:00

[E-bmw]

Get a compression test done.

[E-bmw]

What drove them to change the injector?

[Smint]

If you live anywhere near take it to Albert Lock, Rushden Northants.
If he and his son can't diagnose and sort that no one can.

[paul_c123]

Its possible its just dirty valve seats (ie coked in carbon) which is the issue here, but it could also be a scored bore, and/or a piston ring broken up, and/or the piston skirt broken up.

I have a car which had low compression on one cylinder. Took the head off - which wasn't trivial, I needed to buy a £280 specialist tool to remove the injectors safely for reuse - and didn't find any issue with the valves apart from being filthy (it was a direct injection petrol). So, I filled the cylinders with oil and left it a week, one kept the oil and the other didn't. Suspecting rings, I removed the sump (needed an engine brace bar over the top, since the head was off and the engine was being held on a trolley jack at the time) and the piston/conrod. Close inspection showed damage to the piston.

In parts itself, it didn't cost that much. But it did cost about £500 in extra tools (which I still have, and could sell or reuse on another car another time), and it took a LOT of time up.

https://www.youtube.com/watch?v=I32DfqbGl2Y and https://www.youtube.com/watch?v=fUsI0ypD52k show a similar journey down a rabbithole, he's not even fixed it yet.....

[stevemcs]

Terraclean is pointless, if its rough on idle are you sure there are no airleaks ?

Before changing the injector did they do simple checks like unplug it to see what happens, it seems odd to just change the injector based on the fault code, you would really want to be sure before committing. I don't understand why they thought it would want a regen, if it needed one then they should have carried it out to see the job through.

[E-bmw]

As above, Terraclean will do nothing for valve-train issues if that is what it is.

Did they also do a leak-down test to see where the compression is being lost?

[stevemcs]

Did number 4 injector get tested ? i'm wondering if its knackerd the cylinder up.

[barryrs]

Unfortunately I believe these engines have a known exhaust valve issue.

“A "burnt valve" in an A200 engine, refers to a valve that has been damaged by excessive heat, often due to a poor seal between the valve and its seat. This can lead to a loss of compression, poor engine performance, and potential engine damage.”

[paul_c123]

Low compression --> remove head. There is no shortcut. There is no "fix" which can easily be done without removing the head. I guess it would be possible to diagnose more precisely what it is before removing the head, which might be useful in a scrap/fix decision. But if you're paying for that diagnosis, its just more money to spend and more time spent putting off removing the head.

[Dynion Araf Uchaf]

Maybe buy a cheap boroscope that you can use with an iPhone and stick it down the spark plug wells and see what the bores are like?

[E-bmw]

Dynion Araf Uchaf said:

Maybe buy a cheap boroscope that you can use with an iPhone and stick it down the spark plug wells and see what the bores are like?

Good luck finding one on a diseasel.

Just sayin'.

[Dynion Araf Uchaf]

E-bmw said:

Good luck finding one on a diseasel.

Just sayin'.

didn't twig it was a diesel. Even though I think I had the same engine in a Merc 10 plus years ago now you mention it.
Is it possible to look down the glow plug 'wells' with a boroscope?

[E-bmw]

Dynion Araf Uchaf said:

E-bmw said:

Good luck finding one on a diseasel.

Just sayin'.

didn't twig it was a diesel. Even though I think I had the same engine in a Merc 10 plus years ago now you mention it.
Is it possible to look down the glow plug 'wells' with a boroscope?

It is of course possible, alas they are generally much smaller than a plug hole.