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#1071637 - 08/16/21 05:02 PM Intake manifold retightening  
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Buick Runner Offline
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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 just used a bead of RTV for 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.

Last edited by Buick Runner; 08/16/21 05:09 PM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1071639 - 08/16/21 05:58 PM Re: Intake manifold retightening [Re: Buick Runner]  
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Hunter79764 Offline
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Originally Posted by Buick Runner

The engine is a L69 305 with stock heads and a used ZZ4 intake. The intake is not supposed to have been decked before. ...
Only other thing I can think of is that the manifold to head alignment is somehow off.


This was my first thought. I remember having a leaky intake manifold on my dad's TBI suburban. The original failed somehow (corrosion maybe?), and Grandpa got a good clean used one, supposed to be off a crate motor or something. Installed, leaked coolant. Re-installed, more careful with the RTV etc, bought better gaskets - Ran rough with a vacuum leak. Pulled it again, cleaned surfaces, dad called Grandpa to come over and supervise (he was lead mechanic at the Chevy Dealership, knew his stuff etc.). Everything by the book, still leaked. Grandpa decided to JB Weld the original intake and do everything to clean it up etc. as a temp until a new intake could be found, reinstalled that with a thin layer of RTV smeared on both faces of each gasket and it was fine, no leaks. Grandpa did some measuring of the angles on the intake, determined it had been modified to fit on an engine with milled heads, causing a slight mismatch at the top (or bottom? Memory is fuzzy) of each port. Gaskets sorta sealed different each time, giving different results.


That said, snugging up the bolts can't hurt much and if it works, you saved a bunch of headache.


(grandpa's other trick he used on the old truck at the deer lease isn't recommended, but works in a pinch. He put some gear oil around the vacuum leaks and put some fine sand there until the sand was sludge. Added oil and sand again until there was a pretty good sludge layer. He kept that thing running for years without putting a cent into it. Radiator leaked, so he put in an egg white, then removed the pressure and left the cap on halfway. Plugs fouled out, so he popped the boots off of each plug and rested them on the plug, caused a higher voltage to be able to jump the air gap and burn off the plug fouling. Muffler rusted out, so he RTV's a cereal box then got some sheet metal on the back, wrapped it tight with bailing wire, and ran it another 20 years. Pretty much all the vacuum lines had been wrapped in electrical tape for fixing leaks. I think it was a game for him after he retired to try to keep his mind sharp...)


Shawn

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway
#1071640 - 08/16/21 06:43 PM Re: Intake manifold retightening [Re: Buick Runner]  
Joined: Dec 1999
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86ttop Offline
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the original L69 manifold is hard to beat. I'll bet if you compared two, you'll find they are much the same, Good luck!


Leo Paugh
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#1071650 - 08/17/21 03:48 AM Re: Intake manifold retightening [Re: Buick Runner]  
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Buick Runner Offline
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The biggest difference that I see is the stock manifold has 4 holes for the carb while the ZZ4 has two kidney shaped carb holes. Supposedly the ZZ4 intakes are made by Edelbrock for GM, sometimes Eddy intakes can have fitment issues new out of the box.

I had an issue with a new head gasket on my 46 tractor not sealing. Finally I ran it doing work until it was fully warmed up, then retorqued it and it sealed right up. Just idling wasn't enough. Hopefully the 305's intake will respond just as well.

Last edited by Buick Runner; 08/17/21 07:22 AM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1071709 - 08/20/21 06:46 AM Re: Intake manifold retightening [Re: Buick Runner]  
Joined: Jan 2000
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mmc427ss Online content
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mmc427ss  Online Content
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Pottstown, Pa
Will, if you do pull the intake mike the gaskets top and bottom front to back and do each side in their crush area. This should tell you whether crush is the same across the surfaces. My Chevy SBC has no Chevy parts. It had sealing problems that would show up over extended periods of time. It would push the runner's outside corners, wall between runners. Also port matching made the top of the intake contact area thin. Had 3/16" alum welded to the top of the runner to fix that. Miked the gaskets removed and then plotted how much was to be removed from the intake surfaces to get an even seal across both sides and top to bottom. A trip to the machine shop to mill to my specs and several bucks later had a manifold that fits properly and no pushing out the corners after two years now.
Bob

#1071723 - 08/21/21 03:32 AM Re: Intake manifold retightening [Re: Buick Runner]  
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Buick Runner Offline
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Buick Runner  Offline
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Thanks for the suggestion mmc427ss. Several places say the intake should slightly pinch the bottom of gaskets more than the tops.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1072266 - 10/16/21 06:26 AM Re: Intake manifold retightening [Re: Buick Runner]  
Joined: May 2007
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Buick Runner Offline
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Buick Runner  Offline
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Joined: May 2007
Posts: 5,008
Dharma station 1 the Hydra
Have not updated in a while. I tried retightening the intake manifold and the engine still runs lean. Instead of using carb cleaner I tried the unlit propane torch test. Well I used a MAPP/Oxy torch minus the O2, it has the advantage of the fuel control knob at the tank and a thinner nozzle to fit into tight areas.

Performing this test around the intake manifold gaskets resulted in no change in the idle speed or dwell change from the computer. However, when I tried around the carb mounting gasket the computer responded to the MAPP gas. Next day when everything was cooled down I checked the carb mounting bolt torque and they were all below 60 lb/in. Following GM's instructions I retorqued to 96 in/lb.

Seems like I am often fighting vacuum leaks. Wonder if its gasket relaxation, the bolts loosening, mating surface issues, or my torque wench is off? Currently I have a thick Felpro base gasket installed. I do have two GM base gaskets I can swap out with.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1072269 - 10/16/21 05:35 PM Re: Intake manifold retightening [Re: Buick Runner]  
Joined: May 2007
Posts: 5,008
Buick Runner Offline
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Buick Runner  Offline
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Joined: May 2007
Posts: 5,008
Dharma station 1 the Hydra
I repeated the torch test and several ports at the intanke manifold are leaking on both banks. With two failed intake gaskets there is most likely a fitment issue.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1072271 - 10/17/21 01:14 AM Re: Intake manifold retightening [Re: Buick Runner]  
Joined: Dec 1999
Posts: 11,891
86ttop Offline
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86ttop  Offline
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Brooksville, Fl
frown


Leo Paugh
It's not an attitude, it's just the way I am.
POW*MIA
You are not forgotten
If things improve with age, I must be approaching magnificent. thumbs

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