My intake manifold is cracked and I have not had the time or funds to fix it. My truck is only driven once or twice a week as I have a company vehicle for work, I know my fuel economy is suffering (about 150 miles to a tank of gas on about a 30 gallon tank). What issues could driving with a cracked manifold cause? Thank you.

cracked intake,, that is unusual,,

smear some high temp epoxy or JB weld over it,,

not sure how a vac leak causes poor fuel economy though. maybe hard starting, poor performance,,,
there are folks that will give you a 1 bbl intake for the price of shipping.

Running with a major vac leak can cause one cylinder to run hot and even burn a hole in a piston! I know because it happened to me.

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Dave

1977 d-200 crew cab ex-army pickup wants it's /6 back
1962 Valiant 2 door, 170, three on the tree
1972 d-100 parts truck
80 volare wagon now a parts car

If it is the original aluminum 86 intake manifold, cracks aren't uncommon.

As has already been mentioned, running with a cracked intake leads to super lean conditions and potentially piston and/or valve damage. Don't do it.

Poor engine vacuum can cause poor fuel economy because it screws up the carb metering. If you are still running a lean burn computer a vacuum leak will totally mess up the timing and the fuel mixture.

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Casually looking for a Clifford hyperpak intake for cheap.

Ouch!

or buy an intake from the junkyard. 1 barrel or 2?

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1964 Dart GT

Reed, if you are refering to the two piece die cast aluminum intake, the common failure is not cracking,, it is a failure at the joint, where the top and bottom sections mend together.. Closer to a seam split than a random crack. You are right-on about the Lean Burn,, with that system anything bad is possible.

86ramslantsix,, if you do have a split at an intake seam, the seam runs along the top outside edge of the manifold, a good welder that knows aluminum could fix that on the engine.
Or clean it up real good and close it with epoxy,, been done before,

This would be my fix in a heartbeat as long as it's not a seam failure/separation of the two piece style intake then I'd weld it or toss it.

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1966 Coronet Deluxe

It can cause the power valve to open more often than not on Holley carbs causing them to run very rich...which also can cause one or more cylinders to get washed down and wearing out the rings faster...causing other fun problems...

-D.Idiot

All the failures I have seen on the two piece intakes are cracks in the floor next to the EGR port. :shrug:

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Casually looking for a Clifford hyperpak intake for cheap.

Reed, are these failures on the one or two barrel intakes (or both)?

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1966 Coronet Deluxe

Both.

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Casually looking for a Clifford hyperpak intake for cheap.

Thank you all for the replies. I don't believe it is the 2 piece intake, the previous owner (my neighbor) told me that a mechanic told him it was in fact the intake that is cracked. I do have a 1 bbl intake and it is the original aluminum one if that makes any difference. All I know for sure is it sounds to me like an exhaust leak. Does this help you guys help me any more? Thank you.

if it sounds like an exhaust leak,, it could very well be an exhaust leak

cracked exhaust manifolds are common across all slants. On my 83 D-150, when I pulled the motor and disassembled it I found that the exhaust manifold was cracked,, was not making noise or anything,, so you never know.

the OE gasket between the head and the manifolds could also be shot. An OE style replacement gasket is not much $, pulling the manifolds, cleaning the faces and re installing the manifolds can either be a nice Saturday job or a total pita,,