i have a 1991 f-150 4.9 six and it runs really rugh it has been sitting for two years ran on old gas 25 miles home it has fresh gas now and new fuel felter but it has not helped it bogs down and loses power when driving and you rev it up and it will run smooth for a few more miles then do the same thing i have put two bottles of fuel sestem cleaner in it but it has not helped

 

Hook a vacuum gauge up and a tach see if the engine will maintain a steady rpm of 2000 without losing vacuum or rpm with additional throttle input. If it drops vacuum and or need extra throttle input disconnect your exhaust at the end of the header, this is to test for restrictions in the exhaust. Running bad gas might have melted the insides of the cat and plugged the exhaust.

 

Mine was doing the same exact thing! I have a 302 though I wish I had the 4.9, anyway I kept re-fouling two cylinders. I changed the dirtiest plugs I have ever seen, this may be due to the nasty old gas. She runs like a champ now!

 

You still refuse to check the computer for codes, huh?

 

I guess it's time to check for fuel pressure too

 

i went to my uncle he is a mecanic and i showed him my old fuel filter and it was so cloged you coudent blow thriugh it and it was hevy with rusty gas but he checed the fuel pressure and he sied the fuel pump is shot it is not putting out enough he said it probibly went out do to the amount of restiction in the fuel filter im going to put a new pump in and see thanks every one who gave me advice

 

yeh i love my 4.9 it turend out to be the fuel pump

 

how much was the fuel pump?

 

my uncle is getting me one from the junk yard for 40.00 and brand new are 120.00/160.00 yeh im glad he works there