It all started yesterday I was on way home then check engine light was flashing so i took it to a shop and had it scanned and there was a misfire on 1 and 8. I knew the plenum was bad so I had the hughes plenum repair and we put it in yesterday. Went to start it, it ran and idled fine but I have a bunch of problems such as if I floor the gas pedal it almost dies, the gas pedal is stiff, as soon as you hit the breaks it stops you quickly, and it just doesnt seem to have the power it did before. I work as a car detailer at a ford dealership and hooked it up to there computer diagnostic tool and no codes came up. Not sure on where to begin or if this has anything to do with putting the new intake gasket on or the new plenum. i have the intake bolts at 36ft lbs maybe thats the issue? idk where to go from here

 

Do you have the firing order correct? 1 and 8 are right next to each other, you may have switched wires at distributor. Stiff gas pedal probably means you messed up the throttle cable, make sure nothing is binding up.

Why are your intake bolts torqued so tight? Thats obviously not good.
Intake bolts should be like this
torque bolts 1 through 4 to 72 inch pounds 12 inch pounds at a time
torque bolts 5 through 12 to 72 inch pounds 12 inch pounds at a time
torque all bolts to 72 inch pounds
torque all bolts in sequence to 12 foot pounds
torque all bolts in sequence to 12 foot pounds

 

Thanks for quick reponse! But yes fire order is right. But you think having them so tight is causing th issue? I just realized i was starting to do ft lbs and not inch lbs... Could this be my issue then? Also, after its all said and done all the bolts at the end should only be at 12 inch lbs? Thanks!

 

Hopefully you didn't crush your new intake gaskets, though, you probably did. Your torque values 300% of what they should be. At this point, I would recommend a new set of manifold bolts-- yes, bolts do stretch.

No. After all is said and done, all the bolts should be at 12 foot pounds, NOT inch pounds. There is a huge difference between inch pounds and foot pounds. Even if it's not causing the issue, you need to correct it ASAP. Also, make sure you follow the proper torquing procedure Matt has provided you (I would double-check to be safe, I'm taking his values on faith).

Not for nothing, but directions do come with the Hughes plenum kit. If you don't have them, you can view (AND PRINT) them on their website for free.

 

Definitely sounds like a vacumm issue which I would contribute to a leaking intake gasket. With it runnin spray alot of carb cleaner around the intake to check for leaks.

 

do you notice a misfire at idle?

 

If you torqued them down to tight why are you only misfiring on 1 and 8. And would a vacuum leak like that really cause a misfire?

 

Yes, a vacuum leak after the MAF sensor (like this case) would cause a misfire. I'm willing to bet the OP didn't follow the correct torque pattern; considering, he over-torqued the bolts. That combined with the over-torquing would cause warping to some degree. With cylinders 1 and 8 being on the extreme ends of the manifold, that is where a leak would be most likely to appear (if it is warped).

 

Okay guys sorry for not responding earlier but I took the intake off again and did it again "the right way." Runs like a champ now! Also found the distributor cap wasn't even screwed on the distributor, wonder how long it was like that. Number 8 spark plug was all full of oil and just crappy looking. Threw in new plugs, didn't need wires, cap, or rotor tho they are only 3 months old. But now my truck has a lot more power I love it! The only problem is when you go to start it after it sits over night she will crank for awhile before it finally fires up, what could this be?

 

Check your fuel pressure. Could be air in the lines or your pump slowly dying.