pilotanpia wrote:
My 1995 F53, 460cid runs poorly after being heat soaked.
When engine is cold it runs like gang busters. After a fuel stop and the engine has soaked up the heat due to no airflow through the engine compartment, there is virtually no power at full throttle. Once above 3000 rpm it starts to get power but misses and hesitates. Once up to highway speeds the engine smooths out and runs fine.
I bought the unit with 60,000 miles on it, 6 years ago.
I have replaced the following: fuel pump, spark plugs, ignition module, both coolant temp senders, IAT sender, water pump, radiator, timing cover, thermostat and all related coolant hoses.
I replaced the fuel pump in 2017 because it would only go 35 mph. I was able to hobble it home and make the repair. It was a very easy task, once the fuel was off-loaded. The fuel pump solved the main issue and it runs well until I let it sit for 30-40 minutes during refuelling. One other note, it tends to do better in cooler climates. Not much problem at all in winter months, here in North Idaho.
Most recently, we were coming home from California and our road has one portion about 3/4 mile that is about 7-8% uphill. I could not get past 5 mph using full throttle. It usually pulls the hill at 20-25 mph.
If anyone has any ideas, I would appreciate it.
Kind of a longshot, but I once sort-of repaired a Corvair (flat, air-cooled aluminum 6 cylinder) that did this when hot. The engine had probably been overheated and several steel intake valve seat inserts had loosened in the aluminum cylinder head. They would temporarily pop back up in place when cold, run fine, then drop back down and shroud the intake valves to self-throttle barely over idle as the engine warmed back up. I temporarily "fixed it" by peening the aluminum head material tighter to the steel valve inserts. It unbelievably ran ok that way for the owner until the engine quit entirely which wasn't long, a couple more months maybe.
Otherwise it sounds like the fuel may be boiling in the line somewhere, likely near the engine or less likely close to the exhaust system on back to the tank. Un-pressured gasolines boil between 100 and 400 degrees F, but should usually remain ok, compressed as liquid, for 30-45lb fuel injection. In older carb units, the fuel line pressure was zilch since the fuel pump was not pushing behind it and tended to vapor-lock the pump. Faster speeds do allow a cooler engine compartment that may mysteriously resolve this.
Is there a fuel pressure regulator on the line? I'm guessing that there is, if it's F.I. This regulator may be on a return line for the excess fuel that early Ford pumps used. What is the required fuel pressure and does it maintain this?
Older carb engines sometimes would cook and boil the carb itself if the exhaust cross-over under the carb (within the intake manifold) was somehow permanently stuck in the high cross flow cold-weather position, or one exhaust down-tube was restricted by a dent or such, causing excessive hot intake cross flow. The cross-over heat is intended to vaporize large raw fuel droplets which can't turn well to the cylinders and therefore hit the intake floor during cold weather.
I have also found intermittent intake vacuum leaks on fuel injection that can cause unusual power losses and stalling. F.I. systems run so lean that they are very sensitive to any more air. These type leaks may tend to initially occur during normally high throttle decelerations, such as a vacuum elbow tube temporarily inverting at a break.
Good luck to you,
Wes
Days spent camping are not subtracted from one's total.
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