Had been on here before, had a massive internal engine vacuum leak on the engine , its the LT1...Pulled intake manifold still vacumm leak after I replaced it with new gaskets...smoke testing is showing minor vacumm leaks at some hoses, and the optispark seal, would this cause it to not be able to create vacuum when cranking? also the pcv system, mechanic working on it seems to think something with that might be causing vacuum leak of this proportion,...help...stuck & troubled...THANKS...
I've just pulled my manifold again as I still have a leak underneah. All port/gaskets were soaked in oil.
No oil in motor when i last checked it - not good.
I just bought a felpro tool off ebay to measure the valley but measuring the gap, the manifold is tapering the wrong way on one side.
Also need to find a capable machinist or buy a milling machine myself
Block was decked by a race building shop so have faith in themgetting it right. All measurement i made were spot on.
Heads are new AFR 210's so i don't suspect the build quality on them.
That leaves the Edelbrock manifold as suspect...
just waiting for the tool to measure the valley. Luckily i purchased it before the pound dropped on friday
IF vacuum leaks not under manifold where could it be, all external components are not the problem, appears deep in the engine what next. could it be in the system associated with the PCV?
A vacuum leak would have to be huge to not allow the motor to run.
Vac leaks are usually on hoses on the manifold.
At the top or bottom of the manifold. I fed propane into the crankcase and watched the afr gauge go richer. The PCM regulates the speed so you don't hear it run faster like a carb.
Have you done a compression check ? This should rule out mechanical problems... Head gasket, holed piston, bad/broken/worn rings, bent valves etc.
Have you checked cam timing (ie it's jumped a tooth or two) & or ignition timing?
In order for vacuum to occur during down stroke of piston, there must be a good seal around the cylinder head of engine. The intake valves must be open at the correct time and exhaust vales must close at correct time. In addition, rings must be able to keep air pressure from escaping into crank case of block. As well as pistons with no holes in them.
Even if every vacuum line was disconnected, and intake manifold leak, you would still have some vacuum registering on the vac gauge when you crank engine.
So you need to start checking the mechanical aspects of your engine for problems. As suggested by Mitch, begin with a compression check on all cylinders. Do a leak down test on each cylinder to see how fast compression pressure leaks past rings, head gasket, & valves.
Since a leak down test involves compressed air, if you have a major leak, you should be able to pin point where the leak is. Example, if air is leaking past exhaust valve, you'll hear air flow in tail pipe.
Yes can imagine will confirm with the garage tomorrow as not working over weekend...they are gm trained mechinics ...however nota gm garage....
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