Extreme carbon build up on 1 injector. What is going on?

[WarWagon]

Here are 2 pics of the #7 injector. There is a large build up of carbon on one side of it. See Arrow.

This is one of 3 suspect injectors where it looks like there are larger shims than the others have. The area with the arrow is further up on 3 then the rest.

#1 injector is wet and this would be the failed piston, but, the injector looks like the others.

Just curious as to this injector and the carbon build up. They are going to the install shop to be tested...

 

[Matt Bachand]

Burning oil in that cylinder?

 

[TurboTahoe]

I am not an expert, so others can chime in, but carbon build-up is typically due to an overly-rich condition leading to unburned fuel in the chamber. Perhaps the injector is leaking, or is spraying too much fuel into the cylinder.

-Rob

 

[Matt Bachand]

Was the vehicle driving for any length of time with any sort of condition??

Do you have good compression in the cylinder with that fouled injector?

 

[WarWagon]

Injectors are 15K and 3-4 months old from being rebuilt. Engine ran good. Did not use oil driving around town/freeway unloaded. When put to working hard it was using 1 QT every 500 miles. As this is only double the “normal” 1 qt every 1000 miles – so what. Synthetic oil will be used if this rate continues after the rebuild.

I figure burning oil would be an even coat of carbon. But this is why I ask – maybe someone had seen this before?

Engine has something wrong with a failure in the #1 cyl and is being torn down. This is the #7 injector.

Engine started to smoke on deceleration – puff or two. Figured it was oil and now it may have been the injectors. Could not tell from the smoke. Reminded us of the really old time construction equipment that would smoke like that.

Starter is melted so no compression test – it will be inspected on teardown.

 

[Dave Barbieri]

Injectors are 15K and 3-4 months old from being rebuilt.

I figure burning oil would be an even coat of carbon. But this is why I ask – maybe someone had seen this before?

Carbon build-up around the injector pintle indicates injector leakage. The pintle isn't seating properly against its seat, and you've got injector dribble. If that cylinder were burning oil, the carbon buildup would be shiny. Check that one injector closely. In fact, now would be a good time to recheck all your injectors for pop-off pressure, spray pattern and dribble. Great opportunity to match the pop-off pressure for all your injectors.