My 84 f150 has a leak which was traced to the exhaust manifold gasket. The truck has the 300 4.9 l6 engine, any advice on changing the gasket and would it be better to change the whole manifold while I am there (I can buy the manifold for $150)?
In some cases, it's a direct bolt-in swap. Sometimes there is a tab on the manifold that has to be ground off in order to work with the stock intake. Some people have alternator clearance issues. And, if you put on EFI manifolds, you'll lose the heat pipe going from the stock manifold to the carb, so you'll have to fab up a heat plate to put on the bottom of the intake manifold so that it's heated. Otherwise you can start experiencing carb icing and the engine won't run right.
I don't think I have that heat pipe. The truck had a manuel choke put on it years ago and the heat riser was removed with the hole sealed shut when they did it. Makes for fun on cold New England mornings getting the truck started up. I have thought of trying to rebuild the choke, which would require the new manifold, heat riser and they choke.
Whatever you decide to put on, take the assembled intake/exhaust to a machine shop and have it planed. It's cheap to do, and both the intakes and exhausts are known to warp. That might be what caused your initial problem.
Another item to check before you start removing the entire exhaust manifold would be the exhaust pipe gasket found on your 84 4.9 I6 engine between the exhaust manifold and the header pipe. Later models had a metal to metal fitting at this connection. I understand this gasket was eliminated from this truck because of frequent failure... Might save you a bit of work because a bad exhaust pipe gasket could be mistaken for a bad exhaust manifold or gasket.
Thank you for the tip. I will check more throughly before decided how to go about the task. Seems like it may be a pain to do, though mechanics won't even touch the manifold for leess then around $400 in labour.