dbsoundman

Hey guys, I'm new to exhaust issues, just wondering if you could help point me in the right direction here. My 92 F150 doesn't seem to have too much of an exhaust leak that I can smell in the cab, except when I'm coasting in gear. As soon as I let off the gas basically, I start smelling some exhaust in the cab (not a terrible amount, but enough to notice). I know this is probably partially because there are who knows how many holes I need to patch in the floor (haven't even looked yet), but I'm just curious where in the exhaust system I might find symptoms like this. It seems like most manifold leaks can be smelled no matter what as long as the engine is running more or less.

I'd appreciate any thoughts on where to start looking or what to do.

Thanks!

seschenburg

Well, I've seen manifold bolts/studs loosen and allow exhaust out between the head and the manifold. I've seen donut seals crumble and leak exhaust gas out of those junctions. And I've seen exhaust pipes, mufflers, etc. full of holes.

If it's leaking when you decelerate, it's leaking at other times also. Unless there's a spot that might open as backpressure increases, but I can't imagine where this would be specifically.

To locate a leak...

Obviously, look for soot where it shouldn't be.

Check for loose fasteners at the manifold and elsewhere.

Then there's the bare hand method. Not always effective, but sometimes it works to find those pesky leaks on the back side of something.

If you smoke, crank it up, then puff around the exhaust until your leak blows the smoke around. Not too helpful under the hood with the fan blowing, but you get the idea.

You can also spray carb cleaner in the running engine. This always seems to cause extra smoke out the back end, and should appear at a leak also. Water works too, but that's old school and may not be a good idea for "modern" engines.