Injector issues

[Alboy]

Hi There,

Am having a bit of an issue with a new engine installation on an E63 AMGS.
Bought a new engine, had to replace wiring loom, and replace radiator. After test driving engine, heard a strange noise coming from the 3rd cylinder on the passenger bank. I changed the ignition coils - made no difference, then changed the spark plug - made no difference, then I changed the injectors - solved the issue completely.

Took the engine on another test drive, and then the noise came back. Took out the injector rod again, and it was completely carbonised again. Put on the diagnostic machine, all was fine, checked the compression and all was fine, no warning lights on the ECU.

What could be causing the injectors to carbonise?

 

[Jobsworth]

Doesn’t look like it’s sealing correctly in the cylinder head. It has a teflon seal near the tip. You can see it clearly on the others

 

[StMarks]

Doesn’t look like it’s sealing correctly in the cylinder head. It has a teflon seal near the tip. You can see it clearly on the others

Fwiw I totally agree that the injector is obviously not sealing, judging from the evident carbon residue (aka black death).
However perhaps ^ that teflon was not the cause, but simply a casualty from removing the injector with the residue build up around it.?
The injector has very evidently been leaking for some time, which does not bode well for the integrity of the engine in general imho.??

 

[Petrol Pete]

Not sure it can be called 'the black death' on a petrol engine , but I know what you mean . It's an odd one based on what the OP did during fault finding.

 

[Alboy]

Yes the seal was fine on the injector before installation, and then after the engine has been run for a while this happens.
Am wondering what could cause this?
If there was a problem with the engine, wouldn't it be picked up with the compression testing? All tests indicate no fault. Am wondering if there is something with the fuel injection, ECU or electronics that could do this.

 

[Jobsworth]

I think a very close inspection of where the injector comes through the head into the combustion chamber, both from inside and outside with a borescope is in order to check for a crack or material erosion where the seal sits. I’m feeling it’s a physical fault rather than a fuelling issue