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Discussion Starter #1
I'm new here, so if this has been covered before please point me in the right direction.
That said, here's my story. 1998 S10 4.3L X motor. California smog stuff.
After 4 or 5 trips to the dealer for the "injector problem" I took matters into my hands. I replaced all the injectors with the Bosch aftermarket units and was happy. When I did the wrenching for the injectorectomy I found a lot of oily sludge in the intake manifold. I cleaned it up and put it all together and the truck ran fine and passed our every other year smog tests just fine.
This year the truck started the rough running, missing behavior again so I knew that it would not get by the smog police so I pulled the top off again.
What I found was the same oil and soot mixture that was there before. Cleaned it up. Retained the old injectors, but pulled the O2 sensors and found them loaded with carbon so I replaced them. Today it passed the smog test. Actually came in below the state average for vehicles of this year. So that is good.
But where does this oil in the intake manifold come from? There was a lot of it. There are some blind valleys that were full of oil. It was engine oil, feel it, smell it, put it behind your ear. It was engine oil. Now oil in the intake can come from two places. Down the valve guides, but they are way down those long intake ramps and I would guess that that oil would go directly into the cylinder and get burned.
The other way oil could get into the intake is through the crankcase breather system. Up the PCV valve. But it seemed clean as did the hose going into the manifold.
So it's a mystery. Where does this oil come from, and are the injectors getting a bad rap for a different problem?
Your thoughts.
 

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Age: 15 1/2
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Well before I go off base, let's think about this:
Oil in the intake chamber would suck excess oil into the cylinder on the intake stroke, and would be burned with the gas, blown out through the exhust stoke and quickly plug up and destroy your Cat. But you claim that you passed the smog tests in California????
No. I think it is carbon and gas sludge like most 4.3 get backed up with.
Using seafoam is a good way to blow all that crap out. The 4.3 was made to be beat on from time to time, but at close to $5/gal seafoam will do a good job. There are many seafoam how to threads here.
You also may be in an area of Cal that is dry. The last vortec that I had ran better in heavy rain (the mosture blew the carbon out and the high oxygen caused the O2 to richen the mixture).

Glad to hear you're not a big polluter!
 

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I'm slap happy, bitches!
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ive seen the intake bolts leak oil into the intake also. i always use like a teflon paste sealer, or aviation cement on these things. the vaccuum in the lower chamber can pull oil past the threads on the bolts.
 

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Age: 15 1/2
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That is probably a big cause of Cat failures.

Just make sure that it doesn't have silicone in it, or it will kill your O2 sensors.
 

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Discussion Starter #5
Well before I go off base, let's think about this:
Oil in the intake chamber would suck excess oil into the cylinder on the intake stroke, and would be burned with the gas, blown out through the exhust stoke and quickly plug up and destroy your Cat. But you claim that you passed the smog tests in California????
No. I think it is carbon and gas sludge like most 4.3 get backed up with.
Using seafoam is a good way to blow all that crap out. The 4.3 was made to be beat on from time to time, but at close to $5/gal seafoam will do a good job. There are many seafoam how to threads here.
You also may be in an area of Cal that is dry. The last vortec that I had ran better in heavy rain (the mosture blew the carbon out and the high oxygen caused the O2 to richen the mixture).

Glad to hear you're not a big polluter!
Bill, thanks for the reply.
The more I think about it the more I'm convinced that it's oil being sucked back into the intake through the PVC system. It's not a lot, it takes a couple of years for it to build up to where it's a problem. But once it gets to the level where the oil is finding it's way into the cylinders where it burns and produces soot that gets cycled back into the intake manifold through the EGR system, that's when the problem starts. The carbon mixes with the oil in the intake and creates the mess that I found. It also clogs the O2 sensors and causes the whole system to go off.
As I said, I cleaned as much of the crud as I could, replaced the O2 sensors and the motor ran like a Swiss watch. I guess the Cat did not suffer too much because the smog test was easy. The HC spec max is 54ppm and the measured reading was 8.
I'm going to rig up some kind of filter in the PCV line, perhaps a mayonnaise jar with cotton ball filters and see if any oil comes this way. There should not be any oil in the intake manifold. But, it's a Chevy. By the way, my other truck is a Harley Softail so I know wrenches and oil;-}
 

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Discussion Starter #7
The oil ans soot is from the PCV vapor from the crank case that has settled in the intake
The oil is from the PCV but the soot I'm sure is from the EGR.
I stuck a Gas filter in the PCV line and took the heap for a 75mph spin on the freeway. There is oil in the filter.

 
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