Won't Start When Warm - In A Weird Way
New to this place, but it looks very well put together, here’s my question:
1994 F150 4X4 4.9l 5speed – engine often doesn’t start after being warmed up, it tries, but almost acts like it’s dieseling, shakes around snorts, and all sorts of bad things, has that same smell too. Cycling the ignition switch 10 times often will allow it to start. This only happens in a window of 10 to 40 minutes after the vehicle has been turned off, I could turn it off and immediately restart it all day long, and, if I let it sit for more than 40 minutes (depending on outside temps) it will always start.
More odd information – I have 2 tanks, almost always run off the front tank first, to near empty, then switch to the rear tank, if I run it to near empty and switch back to the front tank I’ll always have between 1/8 and ¼ tank in the front tank. Fuel flow volume is suspicious, I have good fuel pressure – both tanks, but the truck was checked out and I was told that when running on the front tank volume is inadequate, and he suspected the front fuel pump. I however don’t think changing the front fuel pump is going to take care of my starting problem, because the same problem exists when starting off the rear tank. I spoke with another tech and he is suspicious of the fuel tank selector valve because the front tank is clearly getting fuel from the rear somehow, this valve is apparently a spring return valve so cycling the ignition switch might somehow correct the condition. Another suspicion is vapor lock, if that can even happen in a EFI engine, but what I’m told is earlier models with the same engine and EFI system had a small fan that blew directly on the fuel rail (it does sit right above the exhaust manifold), mine however does not have this fan, not sure when Ford did away with that system.
Any insight would be greatly appreciated.