So i've got a pretty much stock 390 that's running like crap. I know we have some weak cylinders, but what's interesting is that when I was checking for vacuum leaks, it started to stumble real bad when the fluid got around the rearmost intake manifold bolts. We isolated the bolts and when I shot fluid right at them the thing almost died. we tried it three different ways and each time it yielded the same results. Checked the torque and wound up with the same results. It doesn't make sense to me, but it might to you. Any ideas?
Replace the intake gaskets.... Have someone give you a hand with lifting the intake off and on the motor..... Them things are freakin' heavy!!!! Ask me how I know......
I'm not really a 390 guy, but if there's a crack or break in the bottom part of the intake gasket anywhere under the manifold, won't it suck from wherever it can? If that was case you would think all the bolts would leak... hmm, I don't know.
Got a little more info. Turns out the intake bolts had been loose and were torqued to spec. That would definitely speak to a deformed intake gasket.
maybe those rear bolts are supposed to have sealer on them? weird that they're right next to a water passage and not leaking water if it was a gasket thing.
Definitely sound like a bad intake gasket.... Bummer, those FE intakes are both heavy and require that you pull the rockers/pushrods to change them. Great time to think about an aluminum intake... LOL.
I think all the guys are right. Back in the late 60s when I knew everything there was to know I had the same problem on a 427 FE and after taking the carb apart I don't remember how many times the old guy at the garage was right, loose intake bolts had allowed the gasket to get sucked in. Funny, now I'm the old guy no one listens to. My manifold was aluminum but it was still not fun.
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