I have a 1994 Ford F-150 4.9 L6 that I have fixed up and would like to DD. When I drive it long enough to get to operating temperature, I will eventually get a headache that is similar to the headache I have gotten in the past when welding in a poorly ventilated area.
The exhaust system has been checked several times via bubble test. There are NO leaks. The shop vac can barely run because of the back pressure when hooked up the the tailpipe.
There is a very small oil leak on one corner of the pushrod cover, which I will be fixing. Other than that, there is no reason to believe that this truck has any source of fumes.
The clutch was replaced recently. I used to be able to smell it burning at highway speeds. That is gone.
If it's not the pushrod cover leak, what else could it be? I've heard of interior plastics and glues outgassing, is that possible on this truck? It has a rubber floor, from the factory.
Any other ideas appreciated.