MASSIVE vacuum leak!!!!

Can't figure this out to save my life. First I have oil pressure problems and now I have a severe vacuum leak? ou: I checked all vacuum lines and booster line and transmission line. Someone in class suggested I check the intake sealing area for a leak and I poured everything I could trying to get the engine to stutter. I ended up just replacing the intake gasket and I still have a vacuum leak! Any ideas? Anyone in the area free this weekend? I could sure use help so I can get this motor out of my mind for now. I'd like to get started on my garage instead of my cars for the time being.

 

try snuffing out a torch and running the torch around all possible places for the leak, the engine should rev when you get the right spot. or this way
http://www.youtube.com/watch?v=mYa8rcHeN3A

 

Did you use the rubber end seals for the intake or a bead of RTV. The rubber ends seals are known for raising the intake manifold too high and causing vacuum leaks.

Quadrajet? If it's an old one, the throttle shafts probably aren't sealed. There's a thread in the Quadrajet section on the proper way to fix this.

What is the car doing that you believe it has a massive vacuum leak?

 

To find the leak, you could also spray some WD40 or carb cleaner at suspected areas. The engine will rev when you've found the leak.

 

Is this the stock manifold, or an aftermarket one?

I discovered the hard way after doing the break in on my 455 that the Performer intake I put on had a threaded mounting boss that was open into a runner.

I still for the life of me don't know what would be mounted there. It isn't on a stock manifold.
o No:

 

It's stock and I found that one out when I did the intake on my 455 also. I just blocked it off since I couldn't figure it out either. But the little engine is pure stock except for an edlebrock carb. (Checked all those seals and what not)

 

So, after I got it running I noticed that it was shaking pretty bad so I went through all the obvious problems.... I checked all spark plug wires, loose vacuum lines, even checked the spark plugs since it had been sitting for 2 years and couldn't figure it out.

So I put my hands over the carb and tried to get it to die. It wouldn't die until I had a rag over with my hands also. I found a couple little spots that were leaking and fixed those, but to no avail. My teacher said it's probably the intake so I tried everything I could to pinpoint around the intake. I tried wd40, starting fluid, even water, but nothing changed.

I caved and replaced the intake gasket anyways since I couldn't remember if I had reused the old one or not. That seemed to help a bunch, but still shakes when the idle slows down to normal.

I got the car to die with my hands over the carb though, so I'm worried when I had the oil pressure problem I may have damaged the camshaft. I couldn't see any bad lobes when I took the intake off, but then again, I didn't roll the motor over or anything to check.

I suppose I can pull the valve covers off this afternoon and make sure all the valves are working. If it's a camshaft I'm just gonna pull the motor again and do it right this time. Including an oil slinger ou:

Oh, and I used the rubber seals on the end. I know I'm supposed to measure and what not to determine whether or not to use them, but I already had the intake bolts halfway tightened and it was around 8 last night so I said screw it and finished it up.

 

What makes you think you have a vacuum leak? If the engine shakes so baddly from a vacuum leak, I think you'd hear it. Is this the same engine that you ran for about 5 mins. with no oil pressure? You may (probably) have one or more lifters with no oil in them causing them to collapse, which in turn the valves will not open enough. Is the valve train noisey? Any chattering or clatter?

 

Same engine yes. I just assumed that if you covered the carb and it still ran then you had a vacuum leak because it was getting air from somewhere eles. Also, when I shut the car off, the carb sounds like it's really sucking air and sorta wheezing. My teacher (GMASEP instructor for 20+ years and really knows his stuff) said that was an indicator of a vacuum leak, but we never moved the conversation onto possible problems caused by the lack of oil pressure.

I do have some noise from the valve train, but it's a little hard to tell until I do my exhaust gaskets because there is a puttering from that as well. I figured the lifters were ok once I got oil coming out of the pushrods (will admit to only checking one side however.

 

Spread bore to square bore adapter plate and I rechecked that one. I put a vacuum gauge on it and it is rather erratic, but when I hold the rpm above 1200 it smooths out a lot. I really really imagine I'm missing something stupid simple, but I tend to over think things so if it's simple don't worry about bringing it up in case I missed it.

 

Erratic Vacuum readings also can be caused by valves. I'd definately pull the valve covers and check things out!

I've used one of those square bore carbs to spread bore intake adapters before and didn't have a problem, but I've heard of them causing vacuum leaks for others.

The line going to the transmision modulator commonly falls off after the molded line moves around durring an intake swap, check tosee it's still connected and the rubber hose in good shape. That can be nearly impossible to hear because it's down near the exhaust.

Rubber end seals are kown for causing vacuum leaks. I'd consider pulling the intake again (yeah, I know it sucks) and using RTV.

Actually, since you aren't sure of the valvetrain's condition after the oil problem, I'd definately pull the intake to check out the cam and lifeters. Put it back together using RTV instead of the end seals.

I've had terrible luck using the stock valley pan for the intake in the past. I always use TA's intake gaskets now and cut out the center of the valley pan for the PCV valve. Never had a vacuum leak using them.

 

Checked the transmission rubber hose. Almost the first thing I did. What would I be checking for on the cam and lifters? I couldn't see any damage just looking while the intake was off, but then again I don't know what a collapsed lifter looks like. Cam seemed ok, but I think there may be a couple lobes that are hard to see without looking specifically. It seems to me that not using the rubber seal would create a high possibility of blowing out the rtv, but I could try that. I will take care of the exhaust gaskets at the same time so I can eliminate that other noise source also.

 

did you possibly warp the carb....tightening it down by feel rather than torque?

 

I doubt I warped it. I don't hear any problems with the carb itself. I always tighten it by feel, and have never had problems with any other cars. I think the car would have at least done something while I was spraying butt loads of starting fluid around the base of the carb.

 

Am I thinking wrong here or not, the end seals ( rubber or RTV ) would only cause an oil leak. All the vacuum should be in the intake manifold and heads before the intake valve. Please set me straight it I'm getting this backazzwords!

 

That's what I thought too so I'm with you on that one.

 

Checked that. If I have vacuum leaks that's almost always the first thing I check since it's happened to a car at school that we rebuilt the booster on and the engine sounded like crap the second you pressed the brake pedal.

 

The reason why the rubber end seals can cause intake gasket leaks is because in some cases the rubber is keeping the intake from seating tight against the gasket and head. All you need to do is a mock up to see if this is a problem or not. Sometimes I use a razor to trim the height of the rubber end peices, this has worked for me.

I agree with the above posting that the TA intake gaskets are far better than the stock style, and I also use only the center part of the intake sheet metal thent he TA gaskets for the intake passages.