I have a '94 VP 5.0Fi (Ford 5.0 EFI) and have been spending the past year trying to troubleshoot a hardstart/idle problem. The engine starts up strong but after it gets past its initial warmup, the idle gets erratic, surges up and down, then eventually sputters out. I replaced the fuel regulator which helped a bit for the starting issue. According to the Seloc manual, I have acceptable, although low, fuel pressure. Engine off I have 38lbs, running I have 32psi.
Normally I would think that the issue could be a vacuum leak but I noticed that with the battery charger on while the engine is running, it runs much better, not perfect, but at least doesn't violently surge. With the charger I get 13.5-14V, without the charger I have 11.7-12.5 from the alternator. I'd love to say its an alternator issue but the fact that the idle still isnt completely smooth and strong has me think otherwise. I also added an IAC too with no improvement.
Any ideas would be greatly appreciated.
Don gave me a link to download manuals for my engine/drive. I have a 95 5.0 ford (carbureted), but some of these manuals do cover the fuel injected fords. Not all of these manuals are necessarily applicable to yours, but they are all Volvo Penta genuine manuals and at least one covers 5.0 fuel injection.
It could be so many things.. whats the story with your battery? is it new? you could be on to something if it does better with higher voltage. i can tell you from ford experience. 11 volts with fuel injection is not going to get it. not enough. that causes problems with all mass air systems. all sensors need 12 or more volts to operate.