'90 4.9L exhaust leak
 

Hi, my first post. My brother has owned a '90 F150 4.9L 4x4 5 speed for 3 years now. He bought it with 81,000 original miles in 2005. Needed ALOT, new front fuel tank, alternator, starter, heater core, radiator. Full tune up, plugs, wires, cap, rotor, O2 sensor, thermostat, serpentine belt. All work performed by me because he really doesn't care. Truck has ALOT of rot.

It has had an exhaust leak, only under load, at any rpm, cold or hot, ever since he bought it. When it starts up, it is tick-free, smooth as butter, as well as idles as smooth as glass. Only ticks when you try to move the truck. And if I think about it, I don't think I've ever heard a gas powered Ford truck NOT tick as it drove down the road.

I've done a preliminary inspection, and the front bank exhaust manifold looks good, both downpipe connections look leak free, no black soot stains that I can see. I have been thinking about it lately and I am considering the EGR pipe.

I've done a search and came up with only 1 relevant post about exhaust leaks. Either exhaust manifold is cracked, gasket is blown out, exhaust manifold stud threads are stripped or the EGR pipe is rotted out.

I am just wondering, since these trucks have been around for awhile, has anyone pinpointed the common exhaust leak problems on stock Fords? This truck is bone stock, has no balls, so it's not like its been revved out in its life ever. My brother just drives it to work and back, and doesn't give a crap about performance. Might have been run low on oil enough to cause the exhaust manifold to leak before he bought it, but since he bought it I've kept up on the maintenance schedule.

Any first hand experience????

exahust leak
 

I canot recall if ford put an exhaust manifold gasket on the efi motors. the carb versions were "dry" fited and leaked alot. Id pull the manifolds and replace that and the connnection doughnut to the muffler the parts cost sould be well under 20 bucks. if you find any cracks just weldem up as they are plain steel and heasy to fix.

start with simple cheep things and rout out the hard ones.

Also look at your thermactor inlets (air pump) they like to rust out bad!

Exhaust leaks are a pretty common problem on 6's because the manifolds clamp down on the corners with washers rather than bolt on. That's one source (manifold to block mating surface). You can try to have the manifolds smoothed down and you can try to use steel-woven exhaust manifold gaskets; people also try graphite grease in place of the exhaust gasket. I don't think they come with a gasket from the factory. Another source is the AIR injection pipe.

A major cause of the ticking under a load , is the air injector pipe that is tapped into the exhaust ports of the head. the legs to the ports from the main air pipe rot away or break loose.

Thanks for the information!!!

No exhaust manifold gaskets from the factory?? That's a first for me.

Looks like the common denominator is the AIR injection tubes. Sounds about right since this tick sounds the same no matter the engine, L6, 302 or 351, I've heard em all and they all tick!!

Thanks again people!

I have the same truck. Exhaust manifold studs are known to rot out and need replacement. Air pipe also rots where it meets exhaust pipe. I've replaced it a few times, but the last time I wrapped the bottom end with some stainless shim stock and clamped it with stainless hose clamps and its lasted longer than any other fix.

My newly acquired 96 Ford F-150 4X4 with 4.9 six had NO exhaust manifold gaskets from the factory. Has the under load tick you are talking about and throwing code 174/Lean burn bank 2. On tear down I noticed signs of downward exhaust leaking out of #2 and more out of #4 ports. l cleaned up mating surfaces and installed a Felpro graphite manifold gasket that covers all ports. Retorqued attaching fasteners in order and put it all back together. Have less of a tick but still throwing code 174 and 171 which is lean burn in both banks. So back to the drawing board. Will have to double gasket the beast and see what happens.