Thread: Please help me understand this....

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Have a CO2 extinguisher handy. You don't want to clean up the mess a dry chem will make, don't ask how I know.

Vacuum leaks from the underside of the intake manifold can be found by performing a simple vacuum gauge test.

1. Remove any breathers and plug or cover their holes in the valve covers with tape.
2. Remove the PCV and plug or cover its hole in the valve cover with tape.
3. Remove the oil dip stick and connect a vacuum gauge to the dip stick housing.
4. Start the motor and read the vacuum gauge.

If the vacuum gauge shows vacuum, you have a leak under the intake manifold.

Hi you guys, here is an update on the SBC that won't fire on cyl. 8. Again compression is 160, did leak down and got air out of the valve cover portal when pressurizing #8. Other cylinders leak air through that hole also to some degree but none through exhaust or carb. Oil is clean (shavings etc.)and the rockers appear to be working well so I don't think I have a flat cam. This is crazy... My neighbor, a pretty good home style mechanic even says WTF!?

I think Denny has nailed it, you probably have a damaged reluctance tooth

More good ideas. Here's more:

-all new plugs
-moved plug wires around, still problem with #8
-HEI dist was new 5 years ago with at most 2 hours of use (but yes could still be bad)
-as noted before, seem to be getting good spark to plug
-dist is tight, no play but the reluctance tooth...? Dont know what that is: help!
-yes the rotor does not seem to point directly at the cap #8 point.... but if its off there wouldn't it be off at all the cap points... but its firing on the other cylinders.
M

How (exactly) did you determine the rotor is misaligned only on #8?

That is extremely odd.