Originally Posted by Grey5.0

So, I've been having some odd issues with my 1978 F100 302ci recently. Only mod is a pair of Hedman long tube headers connected to a true dual 3 inch stainless exhaust (no cats). It has a noticeable stumble on the bottom that is much worse when cold. This usually results in me having to very slowly ease on the throttle or feather the throttle to get it past this point without it coughing and bogging or dying. It not only does this when leaving from a stop, but also sometimes when trying to get it to kick down from third gear (it has a C6).

Additionally, when running at wide open throttle, it'll rev up in first, sometimes normally, but sometimes it seems to start losing power and vacuum pressure and will shift early. In either scenario, when it shifts to second, things get funky. It will instantly start to choke down and lose all power. The only way to fix this once it's started is to immediately let off the gas and start pumping the throttle. If left to coast, it won't re-fire and I have to pull over. After quite a few pumps, it'll kick back up and sputter into life, rolling along like nothing happened.

Additionally, if run then left to sit for between 3-4 hours, then fired back up, it'll knock loudly several times before resuming normal operation. The knocking stops exactly when the oil pressure idiot light goes out on the dash.

I've also noticed that the idle picks up noticeably when the knocking stops. Note that it's a loud heavy knock, not a light tapping or ticking. In a bizarre twist, I used to own a 2005 Jeep Grand Cherokee with a 4.7l V8 that exhibited this same behavior to a tee (referring to the knocking). After doing this for a number of months, the radiator hose ended up getting cut by road debris, causing the engine to overheat. I got a new hose and topped off the coolant, then fired it back up. It then proceeded to eat a valve, then fire said valve back out through the valve cover. When the mechanics pulled the engine apart to fix it, they said that it was sludged up so badly that it was a miracle it ran at all in the prior months. Recently, it's been doing something new.

When it's started up after being left to sit for a while, and sometimes when completely cold, it'll produce a stream of relatively thin, light smoke from the exhaust pipes for about half a minute. This smoke is typically bluish in color, but I'm colorblind, so don't hold me to that... After a few weeks, it began to make little puffs of smoke if I tapped the gas with it in neutral or park (revving to 2,500 rpm at the most).

Now, the volume of smoke it produces seems to be steadily increasing in volume. I'm not sure whether this is unburnt fuel or if it's oil, or a mix of the two. It would also be pertinent to mention that the "mechanics" who worked on the truck for the previous owner had absolutely no idea what they were doing. I had to replace the remanufactured carb that they used because I couldn't get it tuned properly, and always seemed to dump enormous amounts of raw gas into the engine. When I pulled it off, there were a number of pieces not working correctly, including missing jets, explaining the tuning issues. When I replaced the carb with a new one, it ran spectacularly for a few days. On the third day, however, it developed the stutter that I mentioned earlier. It has been vacuum tuned, the fuel pump is brand new, etc, etc.

I'm really at a loss at this point, and I'm just getting ready to either gut the engine and do a full bottom up rebuild, or replace the blasted thing with a new crate engine from Ford Racing.

Originally Posted by HIO Silver

Parsing for readability....