All the parts I have installed has been from Ford(motorcraft) I am going to do a leak-down test today as I was told I might have a slightly bent valve, which is hard to believe since my compression test was 185. but it doesn't hurt to eliminate another possibility.I even performed a capacity discharge (to no avail)

 

I just sent 97shozts a PM but it's under light load or heavy load. if I flog it it seems to go away. I am almost thinking a worn intake cam lobe but with 60K (I'm the original owner) it's hard to imagine that. my only other issue is I seem to lose coolant but I pressure tested it and found no leak and watched Cyl #4 with a bobo-scope and saw no leak(and the plug is always dry)

 

Coolant issue...I'd check the oil for coolant as well as the rest of the cylinders. That's just based off of my experiences though. I presume you haven't noticed any external coolant leaks.

 

I performed a leak-down test and had Zero leakage I also did a exhaust back pressure test to check for a plugged cat it was fine as well- zero on the guage. I was then told that Egr tube in the lower intake likes to plug and cause misfires. I removed the upper intake and found them all clear I removed the valve cover and checked the valve springs and cam/rocker arm travel. again, all good. so I decided to remove the lower intake to check for a leak as I was told this might possibly be an issue too from a Ford Dealer ship friend.I'll keep you posted!! I tell you owning a couple of Citroens and the issues I deal with them pales in comparison to this issue. I'm about ready to drop a weiand intake and a holley carb and cal it done! LOL! thanks for everyone's suggestions they have been really helpful!

 

Hey All,
I finally repaired the issue(#4misfire) it ended up being the lower intake manifold gasket.I removed the lower intake and found that a small amount of coolant was getting into #4 intake(behind the intake manifold flap runner) causing the misfire at partial/full throttle(the coolant port runs right under #1 and #4 cyl and there is a small amount of surface between them)I believe my intake gasket warped and caused this as I checked the manifold with a straight edge) I did notice the new Motorcraft gaskets are a little more beefy and have a thicker rubber sealing surfaces. So 4 months and 400 dollars later it's repaired. I guess it's cheaper than car payments!(trans flush,spark plugs,plug wires, coil pack, intake manifold, injector)I guess it was going to be needed.....eventually! LOL just goes to show even with 30yrs experience(on European cars) one can still be wrong but Thanks F-150 forum for the great feedback at least I'm not alone!

 

I'm have the same problem on a 4.2 with 181,000 miles. changed plugs, coil pak and wires. changed upper intake gasket and still dies under load, going up hills and full throttle.

 

Bank 2 catalyst low means the O2 sensor behind it is bad.

 

Hi Zap: Can you ask your guy in Austin if a 03 or 04 4.2 v6 can be used in a 97 F150. I bought mine back in Aug. of 96 and had a lot of problems with it. It's been down for months and I'm afraid to go with anymore older blocks. Thanks.

 

Hi All: Just wanted to let you guys know that I brought an 08 v6 with 11k miles
to install in my 97 F150 will let you know how it turns out. Any advice that you may have to give may be of a great help. Thanks

 

ahmad start a thread asking for help installing a 4.2L