i got a 94' f150 with a 300 i-6 i bought it cheap from a friend for my cousin. its got 200k but he has been driving it just fine for couple weeks an then the other day the engine lost vaccum. it will idle fine but wont pickup an wont rev or anything an the intake has no vaccum at all. so is there any starting point? i have put new plugs,wires,cap,rotor, etc an tuned it up but i dunno about this vaccum problem an my cousin has no idea either.

 

Finding the source of the vacuum leak would be a good starting point.

 

Maybe start with a can, or cans, of carb cleaner. Spray all the vacuum lines one at a time and look for a change in idle. Spray around the brake booster and intake to. But if it's idling fine but wont rev it doesn't really sound like a vacuum leak to me. Usually a vacuum leak will make it idle rough and smooth out as rpm's increase. What does it do when you try to rev it up?

 

it bogs downs an starts running super rough an wont rev up at all it might make it to 1500rpm. sometimes itll smoke a little just black smoke puff here an there. let off the gas and it goes back to idling bout 750 rpm.

 

Don't really know that much about the FI motors but that sounds like a fuel delivery problem, kind of like a carb being way out of adjustment, or the timing off.

 

Check the fuel filter....Then the plugs....See if they're fouling out...