My 99 F150-4.2 has been a workhourse at 200k mileage with a fresh top end. The truck runs and looks great but when we load up the desert bikes and gear at freeway speeds (1600 RPM ) we get a miss when we head up any type of hill. Take off the overdrive and it runs as smooth as a hot knife going through butter. I've removed the wires from each plug and we are getting power on each lung. Compounding this is a tappet noise when cold... I know I'll need to change those tappets (should have when the heads were off) but can I get to them without removing the heads...

Please help save the old girl before I shoot her for good!!

 

Hey, welcome to FTE!

Question: are you sure it is an engine miss and not a transmission related issue?
You describe a heavier than normal load, low rpm situation, increasing demand (as you start up a hill).
Maybe the transmission is the source of the problem and not the engine.

If it is engine related, you should be able to duplicate the problem by driving in the offending rpm range with OD on or off.
If it occurs in OD at 1600 rpm but not with OD off at 1600 rpm, I'd be looking at transmission and studder at auto shifting out of overdrive.

original transmission?
serviced regularly?


Thanks and again, welcome to FTE

 

That is what I first went to but a very trusted tanny guy did not think it was the torque converter or overdrive. The tranny shift like silk with no detectable slippage ---unless this really is it. It actually "feels" like an engine misfire---but what do I know.... that is why I'm asking you all--the experts..

Oh well---maybe it is that pesky overdrive band clutch --- or whatever they use in that tranny...

 

Check your coil pack and wires, under a heavy load, you need much more power out of the coil to fire the plugs. Change the wires too if they're original.

 

I'm not quite sure how to check the coil pack--- anyone have the how to's on that job??

I did change the wires but I'll take another look at them

 

Mine has the exact same problem. I have found out the over time the catty converters and mufflers have a problem of getting stopped up. I have a friend that has an f150 with the same engine as mine. He has straight pipes on his and it never misses a lick, and it's pretty stout. I am most likely going to run straights also. Where I live straights are illegal, do I care... Not at all. I hope my information helps you out.

 

Thanks--that does make a great deal of sense to me.. The truck has 205k on it and we most likely need a new cat..

I never thought of it before but I'll look into the cost---it certaily would not hurt performance after sooooooo many miles--three boys learning to drive in it and hundreds of desert trips with the bikes--what a truck!!!

 

I wanted to take the time to write this up for others who may be having the same issue I was. I bought an E-150 van that was running and misfiring at idle. Van would drive but accelerated very slowly but eventually would get up to highway speeds. Brought it home, changed out the Cam sensor and Synchronizer. Misfire continued. Previous owner claimed that he had replaced wires and plugs. Pulled those, verified gap on plugs, and they were new wires. At this point the van was still not running right. It also would not show a CEL which is very weird. I have never seen something run that bad and not show a CEL. I went back to the basics and here is what fixed the problem:

1) Gapped plugs to the recommended .054
2) Re-ran the wires, making sure they would not get burned by the exhaust
3) Cleaned the MAF sensor with specific MAF cleaner
4) Cleaned the Crank Sensor, not the plug itself but the outside of the sensor by spraying it with carb cleaner.
5) Purchased and Replaced Ignition Coil pack (looks like brick and is mounted on the passenger side head)
6) Verified all wires were run correctly and were connected well
7) Verified the cam sensor was plugged all the way in, and inspected the wires for nicks or scratches from a pulley (checked good)
8) Replaced battery Terminals, cleaned everything.
9) Checked the ground to the frame from the battery terminal, also checked the ground to the passenger side head from the plug in that goes to the connector for the coil pack.

I know this is a common issue on this engine and hope this helps.

 

Hi, wow it can be such a mystery, I have a 2001 f-150 4.2 V6. Bought the truck from a private seller and it ran great for bout three months and all of the sudden rough running, could not even get up to speed with it or I didn't want to, it just seem to run so rough, I just wanted to get back to the house with it . Anyway truck ran good no over heating, did have a (CEL) on, had it checked, had a #1 misfire, put motor craft plugs in it, good after market wires, checked an double-checked firing order, the one thing I probably should not have done was put an after market coil in it, and the service department told me that, I'm really baffled the truck was ruing good for an older Truck with right at 160,000 miles, I am now focusing on maybe a vacuum leak or fuel, exhaust system, I feel like I need to do that before changing the coil again, trouble this matter would be the easiest and cheapest way to. thanks for reading, I'd love to know your opinion.