P0303 code. Changed plugs, wires, coil, injector 3. Serviced all grounds and electrical connections I could see while intake manifold was off. Fresh IM gaskets. Seems like fuel is not getting to #3 which is passenger side rearmost cylinder. When I park it uphill, it runs great. Level or downhill, misfire happens right after starting, check engine light comes on, P0303 code. Park uphill, wait 5 minutes while clearing code, starts with no misfire and runs great. This is making me nuts. Is there a check valve on the fuel rail? Is my fuel pump weak? Is the system prone to vapour lock or fuel draining back?

Any input greatly appreciated

 

Welcome to the forum

1998-2011 Rangers run 60psi pressure in fuel system, from tank to engine, 60psi
Engine bay would literally have to be on fire to get a vapor lock in the fuel rail, or in the line from tank to engine

Older vehicles got vapor lock on hot days because they had 0psi fuel pressure from tank to mechanical fuel pump on engine
And 0psi pressure in float bowl
As pressure goes up gasoline needs to get very very hot to vaporize
Just FYI

Steady misfire means you need to do a compression test on all cylinders first, just to rule that out
Remove all 6 spark plugs first
Test each cylinders compression and write it down
4.0l SOHC should be around 170psi
But what you are really after is an average(for your compression gauge) and 1 cylinder that's much lower than the others, this usually means a leaking exhaust valve, that's the most common issue on any engine

Once that is out of the way, compression issue ruled out, then you can look at spark or fuel for the cause of the misfire
If you don't do compression test first then you will be wasting time, and some money, on non-fixes if it is a compression issue
Unlike spark and fuel issue compression is black or white, no grey area there