For all the gearheads out there

[gregzz4]

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

[hillegom]

So how does that happen Greg, faulty install?
Yet it worked all this time, and fails now?

[gregzz4]

Can't for sure say why it failed
All I can think of is it slipped down a bit during the install, and the gasket ports are 'just' a bit big, allowing it to find an edge of the head
Then over time it failed

This last set of gaskets was on there for 2-1/2 years without issue 'till the middle of October, so go figure

I checked the intake with a straight edge and all is good
I checked the intake bolts before removing and all was torqued

No explanation here, but I'm just a hack with this stuff

As I stated earlier, I used some 'poop' this time to keep the gaskets centered over the ports and expect this to work

[sirruckus]

glad to hear you found the problem - at least its relatively easy fix

[gregzz4]

One other thing that comes to mind is while I was sitting in air care at the end of August and she got warm for about an hour maybe that allowed the intake manifold the warp just a slight bit and gave room for the gasket to crack
Then when I put the distributor back in last weekend I got it off by one cylinder and it backfired a couple times
This may have blown the gasket out when it was originally only cracked
As I said I can't say for sure

[hillegom]

Well, your troubleshooting skills rock!