Intake manifold leak-how would I know?

[richy rich]

K so my 87 has slightly poor throttle respone,oil on the back of the motor,& it get knock with very little boost[say 13lbs w 94 octane].So I started thinking about the intake not sealing at the back[this seems to be where the oil leak is]that would also cause a lean condition[am I right?]BUT would a bad intake gasket show up on a vacum gauge at idle?Im like 17lbs idle-what should it be?[in park,or gear/hot or cold?]Thanks guys

 

[BlackMetal]

If the leak was bad enough to cause performance issues I think it would also appear on your gauge. 17" is good vaccum for these cars. I'm chasing a leak as well and I only have 12" of vacuum but don't have any of the performance issues that you mention. I think your problems might have a different cause if you're getting good vacuum like that....

 

[richy rich]

K so 17ish seems ok?well thats good to know,unless it only leaks[sucks air in] under boost.Man these cars are finiky-LOL,When I told my local GN friends I was going to toss a Big block in it,they almost Tossed me out!LOL

 

[Phoneguy]

You wont get a vac leak at the back of the intake. Oil leak yes.

 

[GNVYUS 1]

Fighters Garage, lc. ( bottom of page )

I am doing a full boost leak test this friday when it arrives.

 

[BlackMetal]

Fighters Garage, lc. ( bottom of page )

I am doing a full boost leak test this friday when it arrives.

Seems like a pretty handy tool. Let us know how it goes.

 

[turbo nasty]

Just recently did this with a soup can that I made up with a bolt on tire valve and then I pulled the rocker shafts for both banks and psi'd the motor to 30 psi and discovered 3 ports leaqking on the intake and also the alum vac block fittings were assem dry w/o sealant and all were leaking. Test was through the compressor inlet

 

[notacarlo]

Car running (idle) get some carb cleaner and spray around the top of motor. The engine will stumble when you get to the leak.

 

[vacuum 6]

Seems like a pretty handy tool. Let us know how it goes.

Yes DR.BOOSTER let us know.

 

[notacarlo]

Too bad it only goes to 30 psi

 

[turbo nasty]

Car running (idle) get some carb cleaner and spray around the top of motor. The engine will stumble when you get to the leak.

Nope it will not always affect ....I tried propane, brake cleaner, carb cleaner, wd40 with no effect. The psi test reveled it with soap bubbles. U would think the engine would have changed/bog/rev enough with spraying the various items around and on all areas, but they did not.

 

[vacuum 6]

Just made my own. Beaded steel 3" pipe with cap and valve stem. Dont really need a gauge mounted on it, I have a tire fill valve with built in gauge.

 

[GNVYUS 1]

That kit is pretty crappy, had 2 pin hole leaks I had to seal shut, then the valve leaked and the damn thing is 2 13/16ths so you need to help it seal against the hose.

I am sending it back when I figure out how to stop my injector o rings from leaking.

You don't need 30psi to test your system with, I found 3 leaks at only 7-9psi. If I get another tester or they fix this one I will only go to 20psi.

I tried using plumbing products but they all turned out to be either a hair to small or to big for a 3" hose. I got one at 4" which fit the reducer hose and I got the bike valve but then the 3" hose wouldn't fit over my inlet pipe?? AHAHAHA!!

Mark at BuickGN has one without the gauge now.

 

[vacuum 6]

You don't need 30psi to test your system with, I found 3 leaks at only 7-9psi. If I get another tester or they fix this one I will only go to 20psi.

I tried using plumbing products but they all turned out to be either a hair to small or to big for a 3" hose. I got one at 4" which fit the reducer hose and I got the bike valve but then the 3" hose wouldn't fit over my inlet pipe?? AHAHAHA!!

Mark at BuickGN has one without the gauge now.

How did you hook it up? Before or after turbo?

 

[TurboBuickSix]

Boost pressure tester

Don't have a pic but I made one with a 12" or so piece of copper pipe(3")and squeezed one end together in a big vise then soldered it shut. Took a brass fitting that would thread shop air line fitting and soldered that in the side of the pipe.I just used my regulated compressed air supply but you could add another bung or a T for a gauge.Took about an hour made from scraps and crap lying around the garage and works great,also slides right into the 3" no problem.

 

[vacuum 6]

Yeah but where did you hook it up too MAF pipe, up-pipe, where?????

 

[TurboBuickSix]

Yeah but where did you hook it up too MAF pipe, up-pipe, where?????

Compressor inlet(te-60)

 

[turbo2nr]

I wouldn't stress out about a few tiny soapy bubbles at 30PSI.

That's got to be what, .1 CFM out of 600++

Big deal! I doubt that would cause any performance loss.

 

[turbo nasty]

Big Deal huh....Tiny soap bubbles.

I recall no mention of "Tiny" soap bubbles.
I believe the phrase was...."with soap bubbles".
Now a jump to the conclusion of the fact that you assume the leaks were very small seeps would result in "Tiny"soap bubbles.
That was not the case at all.....

If u re read the post and not add words or extra interpretation ....

I tested it "TO" 30 psi and maybe I was not specific at what psi the intake started leaking which was 11 psi on one port and 17 on the other 2.
I've had the the IC piping connections act like a pop off valve at 18-19 PSI and would have a dead seal up to that psi then start leaking then it would reseal back at 15 psi.
Furthermore the soap bubbles on the 2 ports on the pass side at 24 psi was seeping enough to feel it on your hand at 6 inches. Mind you the valley pan side of the intake may have been leaking as well on the same or more ports.

As well as the intake leaking the leaks from the alum vac block was considerable enough to be greatly concerned.

FWIW my outlook is if you are leak testing it then whats 4-6 more psi than what is a common psi with alky or race gas which is avg around 23-27 psi.

This was on a 164 k engine that never had the intake off.

 

[TurboBuickSix]

Did you remember to check the throttle body bushings too?