First let me start off with it is a 98 F-150 4.6 with 212,000 miles on it. And it has been running fine. Last week driving to work and deer runs out. I nail the brakes(harder then I ever have before), yank the wheel skid right around him. Well 1/2 mile down the road truck starts missing, bucking and running rough. I scan it as soon as I get to work. It says cyl #8 missing. Change the plug, the wire and the coil pack to that bank of cyls, I even go as far as changing the injector. Start it up sounds fine, get down the road a bit, same thing. Come back in scan it CYL #8 missing. Do a compression check come back all about the same 175. Check it a few more time fine, then I check it again and it instead of 5 revolution to build up now it take 10. Do it again and comes back fine. Then with no pattern at all, every once in a while it takes twice as long to build up pressure. Could it be that the force of the emergency stop broke something internally? Should I change the other wires, plugs and coilpack, do they run together or something? Any ideas would be helpfull.
I'd borrow or rent a borescope and take a look inside that cylinder - and possibly pull the valve cover and check the valvetrain. The slow compression buildup doesn't sound so good to me.
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2003 F150XL 4.2 short cab/bed 4x2 5 speed manual 3.55 LS
Pulled the valve cover off and nothing visibly wrong. As for the slow build up, like I said it happened once or twice and then never happened again. It would build pressure just like the other ones.
Well you covered the bases, good job. Yea this is pretty strange, -not an ignition problem. Sounds like a tweaked valve or damaged seat. I've heard of the rocker coming loose in the past, but you didn't see anything. Double check that, seems like you would have found that pulling the cover tho.
Well you covered the bases, good job. Yea this is pretty strange, -not an ignition problem. Sounds like a tweaked valve or damaged seat. I've heard of the rocker coming loose in the past, but you didn't see anything. Double check that, seems like you would have found that pulling the cover tho.
I agree. I would remove the cam cover and look again. Sounds like you had a follower pop off on number 8. Sometimes they will get dislocated but stay close to the same positon and look ok. The lash adjuster end of the follower can slide off the lash adjuster tip... It could be the intake follower and you are trying to pull air to compress from the exhaust valve. Which doesn't work very well. A sudden drop in oil pressure may have allowed the lash adjuster to momentarily go soft and that can allow the follower to come off. I used to always reach in there and grab the followers with my fingers and try to move them. If there is any rocking or movement then its suspect. It may be just laying in the head under the cam area. If thats what happened then you should be able to just reinstall the lash adjuster and be good to go. Good luck
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