Retightening intake manifold?

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Clone TIE Pilot

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Aug 14, 2011
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Trying to diagnoses a lean and uneven idle issue I have been having. Just did a vacuum test of the crankcase at the PVC grommet to see if there was an underside intake manifold vacuum leak. Results were positive pressure so no leaks there. Next tried the old carb cleaner spray test. Every intake port I sprayed increased idle, sadly this may mean all the intake ports are leaking vacuum? Surprising it even runs if that is the case. Number 8 seems to increase the RPM the most when I spray there. Overall the passenger side seems to be leaking the most. This is my second set of intake gaskets and it previously developed a vacuum leak at cylinder 8 before. The coolant ports are not leaking which is some good news, only vacuum leaks.

The engine is a L69 305 with stock heads and a used ZZ4 intake. The intake is not supposed to have been decked before. Previous intake gaskets were Fel Pro 1256s printoseals. Current gaskets are GM ZZ4 intake gaskets which are metal shims with a thin grey coating. Both times I used a bead of RTV on the China walls. Before I start dismantling the intake again, I wonder if I should try retightening the intake manifold bolts? With the carb still on I can't reach the middle intake bolts with a torque wench so I would have to just retighten them by feel.

Only other thing I can think of is that the manifold to head alignment is somehow off. If I do pull the intake off I will try to measure the alignment. I still have the stock L69 intake, kinda hate to downgrade back to it but I guess there isn't much difference between the two.
 
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g0thiac

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Sep 6, 2020
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Trying to diagnoses a lean and uneven idle issue I have been having. Just did a vacuum test of the crankcase at the PVC grommet to see if there was an underside intake manifold vacuum leak. Results were positive pressure so no leaks there. Next tried the old carb cleaner spray test. Every intake port I sprayed increased idle, sadly this may mean all the intake ports are leaking vacuum? Surprising it even runs if that is the case. Number 8 seems to increase the RPM the most when I spray there. Overall the passenger side seems to be leaking the most. This is my second set of intake gaskets and it previously developed a vacuum leak at cylinder 8 before. The coolant ports are not leaking which is some good news, only vacuum leaks.

The engine is a L69 305 with stock heads and a used ZZ4 intake. The intake is not supposed to have been decked before. Previous intake gaskets were Fel Pro 1256s printoseals. Current gaskets are GM ZZ4 intake gaskets which are metal shims with a thin grey coating. Both times I used a bead of RTV on the China walls. Before I start dismantling the intake again, I wonder if I should try retightening the intake manifold bolts? With the carb still on I can't reach the middle intake bolts with a torque wench so I would have to just retighten them by feel.

Only other thing I can think of is that the manifold to head alignment is somehow off. If I do pull the intake off I will try to measure the alignment. I still have the stock L69 intake, kinda hate to downgrade back to it but I guess there isn't much difference between the two.
If spraying around the intake there causes a change in idle, then you either haven’t tightened things good enough or your gasket isn’t working as it should.

I’ve read that those metal shimmed gaskets can be a PITA too, so you may want to choose something else.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,827
2,564
113
Galaxy far far away
Been a while since I last updated about this issue. Retightening the intake bolts did not reslove the leaks. Several ports on both banks are still leaking vacuum. I detected this using the unlit propane torch method. Looks like the intake will need to be pulled and checked for warpage.
 
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