Vacuum Present In Crankcase

[tabaka]

sorry if this has been answered before. I found it last night through a search and now I can't find it again.

 

I have a '99 Tahoe with the Vortec 5.7

 

I've got a number 6 cylinder misfire code. I've confirmed that the injector is being told to fire and I've confirmed that the injector is flowing. I've confirmed that I have compression at 180 lbs and spark.

 

It keeps fouling the plug pretty bad and will look oily and crudded up after as few as 50 miles. When I pull the spark plug wire off that cylinder the idle gets a little rougher but it's barely noticeable compared to pulling a wire off an adjacent cylinder.

 

I saw somewhere on here that it could be an intake leak under the manifold and that to test this I should pull the PCV and the fresh air port, plug both and hook a vacuum gauge to the dipstick tube.

 

I am asking for confirmation about that test procedure. Should I get a little bit of pressure out of the crankcase if it is sealed right? If it's reading a vacuum is that for sure an intake seal leak?

 

The only code I'm getting is the P0306. I don't have a real high end scan tool but I can read other data streams like fuel trim. What numbers would I be looking for to see if one side is running leaner than the other?

 

Thanks

Dan

 

p.s. it won't be related to the SCPI tappet problems because I upgraded to the MFI kit when I first bought the truck.

[fixitmann]

What do you have for vac reading {with engine at operating temp}? was compression test done wet after dry were #s higher ,how many miles on engine.

[tabaka]

Engine was warm.

 

Cylinder was dry and compression was at 185 (others were 2 - 180, 4 - 178, & 8 - 182)

* I didn't test the right bank yet.

 

198,000 miles on the rig and engine appears to be original.

 

No modifications other than changing out the SCPI to the MFI injection spiders.

 

Blocking off the fresh air intake on the left rocker and blocking off the PCV grommet on the right cover it reads 17 pounds of vacuum at the oil dipstick.

 

MAP sensor reading 9.0

Airflow at 19.24

RPM 637

fuel pressure 56

 

all I've got is open loop (Det) #s for the O2 sensors as I was torturing the old girl when I did the last freeze frame recording.

[markw8]

With that many miles, I would think valve guides or seals. Mark.

[fixitmann]

I ask Again, what is the vacuum at the intake manifold not dip tube? Watch needle see if it fluctuates especially with increase in rpm.Worn v guides will cause this and the seals leaking is what is causing that plug to foul.does it smoke first start in the morning, more than usual.oil seeps past seal from top of head slides through them worn guides and sits on the piston waiting to be slammed into plug.any noise associated with problem? The culprit here could be a broken spring that let stem wear down guide over time.