91 7.3 injector - Diesel Forum

dwarren · 07-20-2007, 04:28 PM

just replaced all the injectors on my 91 250 7.3.roughly 140,000 on them.question is all but 1 came out pretty clean,the 1 in question is on the right side 4th back from front.it had a heavy carbon buildup from almost the tip to the top.heavy lumpy buildup.lets hear some ideas what might have caused this.thanks don

DSBlack · 07-20-2007, 06:55 PM

Leaking copper gasket... Not torqued properly on install.

dwarren · 07-20-2007, 08:32 PM

ds,when i took it out i had to use a 4ft pipe to give me enough to break it loose,that was the only one that was that tight.the washer looked good and i couldnt see any cracks.Don

DSBlack · 07-21-2007, 09:54 AM

I would guess it was that tight due to the crud around it.
Did you make sure to get all of the gaskets out and check the seat in the head.

My money would still be on a leak fron the seal on the injector to the head.

OkieGringo · 07-21-2007, 10:17 AM

There is a special tool, an injector seat cleaner, that screws into the hole, then turn the top lug and knives cut the crap outta there. But, were you can buy/rent/borrow one I haven't a clue. OkieGringo

icanfixall · 07-21-2007, 01:19 PM

That tool costs about $400.00..... Mine is loaned out at this time so keep looking around for one. They are rare too. [img]/ubbthreads/images/graemlins/smokin.gif[/img]

dwarren · 07-21-2007, 05:21 PM

it doesnt seem to make it run any differant.could it be the cup they talk about when assembling that it doesnt fall out? could it be damaged.?the injector tip was fine.there was not any signs of leaks at the gasket.put new injectors in because i am getting ready to put a sidewinder kit on it.

Airmotive · 07-23-2007, 11:46 PM

There's a thing called "carbon jacking" that we occasionally see with fuel spray nozzles on jet engines (the other oil burners!).

It works like this:
The fuel spray nozzle (or in your case, injector) heats up and expands a little more slowly than the engine that it's screwed into. Couple that with a poorly sealing gasket and you get a small fuel leak. This fuel settles in the tiny gap between the injector and the engine and then the fuel cooks and turns to carbon.

This carbon is very hard an incompressible. So after engine shutdown, as everything begins to cool and return to original dimensions, the carbon that has settled between the nozzle and the engine forces the threads on the nozzle to stretch a bit.

The next time you start the engine, the process repeats. Each time, you lay down another one-millionth-of-an-inch of carbon between the fuel nozzle and the engine. You end up with, effectively, an incompressible carbon washer stuffed between the injector and engine...putting extreme pressure on the threads.

On a jet engine, I've seen this lead to failure of an engine's combustion chamber. Fugly!

I am only theorizing that this is what's going on with your baby...but it's a theory that sounds like it fits!