Hello everyone! I have a 1997 expedition w/156k mile on the clock. It has ran flawlessly over the past 5yrs that I have owned the truck. But now it runs very rough and lacks power and sounds like backfireing through the intake. It first started when the CEN light produced a misfire cyl 4. Since then I have changed both coil packs($49 each),Changed plug wires($81 set), Changed autolite spark plugs($28), replaced fuel pump(pressure was low at 20psi at idle) ($110). I have reset the codes and now I have the same rough running truck that i had before. Now it says that I have a misfire on cyl #1,#7, and #4. Im totally confused. Been working on the problem for close to 3wks now, Its driving me nuts!! any help would be appreciated thanks

 

Did you check the compression when the plugs were out of the indicated cylinders?
My 4.6 had 2 cyls loose comp out of the blue at 138k was some type of valve failure.

 

My brother has a 98 F150 with the 4.6 that had a similar problem. After trying many different things we pulled the valve covers and put compressed air into the sparkplug holes and rolled the engine over to make sure both valves were closed. Air would come back through the intake side on 2 cylinders. If the rockers were pulled out, they would hold air. Turns out that 2 of the intake valves were over cupped (almost like they were being pulled into the seats). Therefore becoming longer from the face of the valve to the end of the stem and not seating. We replaced the valves and it runs great. We never did find out why it did that, maybe due to running lean and getting the valves hot enough to strech?? Good luck.

 

I have been reading what was posted in this thread, and it is a coincidence indeed.

I had a misfire, and turned out two adjacent cylinders on my 1999 F150 V8 were without compression. Pulled the heads, and just like was mentioned above, two intake valves were cupped and lengthened, where they would not seat.

I am inclined to agree that a lean condition caused it, but could not find anything wrong, so just changed the fuel filter, and put in all new intake valves that I purchased at Napa. These valves are not so hollowed out in the centers either, which could have contributed to the problem.

Engine runs like new now. With Gaskets, valves, and new head bolts (as they stretch); I paid out about $400.00, which is a whole lot cheaper than a new engine.

Just thought this might help someone out.

All have a great evening.

Jack, in central California.

 

hi my name is nathan and i did all that too my 86 ford truck 5.0 and it is still back fireing it has a hole in the mullifer would that make it do that

 

I ended up replacing the whole dam engine, I thought it could have been just the valves but I said heck with it.

This is a known problem on these engines. Nathan your engine is different.

 

Nathan, your muffler wouldn't cause that. I would sooner suspect ignition problem or timing, or valve timing.

However, you do need to run a compression check on all cylinders to see where they are. I did (mentioned on an earlier post in this thread) that valve job two years ago, and this thing runs absolutely perfect. Those original valves were really hollowed out, and and so I replaced em all from Napa, which are much sturdier valves at the head.

I still am not positive what caused the intakes to fail, but to be safe, replaced all the intake and exhaust valves, as this engine is very expensive and not easy to pull out either.

Jack

 

could it be my coil no fireing iv been told that most of the time they jest quit but sometimg they work some times would that make it back fire i have put my timeing gun on my truck it is dead on i have dont all the test that u can do on this motor could a bad Choke

 

hey pal do u think it could be my coil not working i have replaced all outher parts plugs and the the cap and botton the wires and all the thr relays and all that stuff u think maby becuse i renewed all that stuff that made my coil good bad

thanks for helping me with the rest of the ? that i had