Not really anything to do with helping to diagnose the problem, but kind of related just the same.
Back when I was 19 I bought my first E-body which I believed to be a '72 Chally 340 Rallye. I didn't know anything about VIN, Fender-Tag, or engine block codes so I just had to believe what my eyes were seeing. The "340" looked all OEM complete with iron four-barrel intake and a Thermoquad topped by a factory orange dual snorkel "340 four-barrel" stickered air cleaner. A few weeks later a Mopar knowledgeable friend was checking out my new ride and commented that the exhaust manifolds didn't look like 340 manifolds. He then rubbed the block clean below the front of the left cylinder head and sure enough it was a 318. Further digging revealed the heads to be 318 too. Someone had swapped on a 340 induction system and a couple of "340 four barrel" emblems to the hood and I bought it hook line and sinker. I was pissed!
But here is the deal, even though it had the big port 340 intake grossly mis-matched to the small port 318 heads; it ran like a champ! It wasn't a power-house, but it had a smooth silky idle, ran out really well and was relatively good on gas mileage. From how it ran, I would never had known any differently if someone hadn't pointed it out to me.
As for your problem, they may, or may not be related.
Oil leak on the back edge of the intake should not have anything to do with driveability. The seal could be leaking just because it was installed improperly, is old and brittle, or any number of things. If everything else is okay, an oil leak from that seal should have no effect on the driveability of the engine ...
unless ... it is leaking there (and probably in the front too) because the intake manifold can not come down enough to put the necessary compression on the seal. What would cause that? If the block or block mating surface of the heads have been milled without the intake mating surface of the heads or intake manifold being milled, the intake will sit up "high" on the heads and not align properly. In extreme cases it will be so misaligned that you can't even get the intake bolted up to the heads! If you can get it bolted up to the heads you could have oil leaks front and rear, coolant leaks, and yes, vacuum leaks from the misaligned ports. However, since you state that yours is only leaking from the rear seal, I would assume that the alignment of the intake is not the issue and that you just have an oil leak, and a driveability problem that is not associated to the oil leak.
Driveability issues can be any number of things. Given the symptoms that you cited (low power, poor economy, low vacuum, inconsistent vacuum) I would start with the basics:
- Visually inspect for something obvious - inspect all vacuum lines and hoses for proper fit and function. Inspect PCV valve and ensure PCV hose is not clogged.
- Inspect carb and manifold gaskets for damage (I had one where a corner of the carb base gasket was literally gone!). You could check for vacuum leak by carefully spraying engine cold starting fluid at carb base gasket and intake manifold gaskets (this is my personal technique and I am not saying that you should do it as starting fluid is extremely flammable. Proceed with extreme caution if you do). If the engine speed increases when you do - you have a vacuum leak at that point.
- Complete a compression test - first dry and then wet (a little oil injected into the spark plug hole).
- Complete a leak-down test. This is one of my favorite diagnostic tools as if you do have low compression it will help determine whether or not the problem is due to worn cylinders/rings, valves, head gasket, or any combination of them.
Good luck and keep us posted on your progress!
Topic: Intake manifold not sealing properly - what are some of the effects. (Read 4592 times)
