I've been having a bunch of problems with my engine lately
It passed AirCare in Sept, then started to act up
It's a GM Performance Parts ZZ4 (hence my username) 350HO crate motor with less than 50K miles on it that I bought brand new back in 2001
It's been idling rough, sputtering/missing on light acceleration, bogging down and sputtering big when the lockup converter activates, vacuum down to 15 inches and dropping to 10 sometimes for a brief bit, running-on on shutdown, and generally being a cow
It still had rolling power, but nothing to overcome the 10-bolt posi and was not 'all there'
I replaced the old ignition leads as their resistance was way up - 600 through 1100. The new leads are 78 - 123 depending on length
I replace the plugs, cap and rotor. No change
I replaced the pickup coil. Marginal change, but not fixed
I tested compression dry - 195-205 all around
I found #4 plug to be oily wet, so I remove it's lead from the dizzy and there was lots of spark. Same when removed from the plug end
This lead me to only one conclusion; a massive vacuum leak under the intake from the oil valley
Well, guess what I found today ....
I'm super happy I found the issue and it's all fixed now
Idle is back to normal, vacuum is back to 17-18 inches, and tons of power again. And I get to drive it to work tomorrow after leaving it parked 'till I had the time to fix it
I used the same Fel-pro gasket set this time, but I used some aviation form-a-gasket around the intake ports on the head side to stop them from slipping
I know, they look a 'tad' big for the ports, but I think they'll do otherwise I would have bought the expensive GM ones
If they do let go again you can be sure I'll be buying them from GM