That's the question! Few months ago I took off my UIM and much to my surprise, I found pretty heavy carbon/oil deposits in the rear secondary of the UIM and LIM. No significant amount of oil was found upstream in the TB or the turbo piping--so why is that one pipe getting gooked up with carbon/oil? The other three pipes were sparkling clean.

Here's a pic of the same thing--look at the LIM only, just disregard the engine, I ripped the pic from another thread.

 

isn't the EGR slapped on the back of the LIM on a Stock TII, pretty sure i remember pulling that bastard of there a few years back... thats yer culprit right there

 

It's reversion.
Fuel and oil (via the oil injectors) can shoot up through the intake tract due to the intake port timing and / or the secondary progressive throttle system.
It's normal.


-Ted

 

I thought all that oil was from the PCV system? is that why intakes get all black on the inside after 15 years? is it a combination of the PCV and what your talking about ted?

btw your pics on your TB mod page are no longer clickable.

 

Would that happen even if I don't have oil injectors? I'm running full premix with no OMP. And why would it be just that one secondary pipe?

Are you saying you have seen this on quite a few cars? Sorry for all the questions, I'm just curious why this occurs.

TIA,

Scott

 

Yes, it happens even if you don't have the oil injectors. Fuel travels back up, leaving the carbon deposits. It's totally normal.

 

As Aaron Cake stated, fuel injectors by themselves will cause this to happen.
So, unless you remove the oil injection and the gasoline (propane? ), you will run into this "problem".


Yes, I see it all the time.
This does not affect performance significantly.
About the only thing you can do to minimize this "problem" is port all your intake ports identically - this is next to impossible to do on an NA due to the 6-ports, but on turbos it's easier - and remove the progressive linkage on the throttle body.
Having identical intake port timing on all four ports and the throttle body mod will open all runners at the same time will minimize this reversion effect, .


-Ted

 

OK, thanks fellas.

Looks like I won't worry too much about it then.

Scott