I have an '88 F-150 w 4.9 FI-6 cyldr that has 144K miles on it.
Since I've owned it, I've kept it mantenenced and recently (about 6 months ago) performed a tune up which included: New: plugs, wires, rotor, dist cap, fuel filter, air filter. I also run a bootle of Fuel injector cleaner about once a month and use almost exclusively Quik-Trip "regular" gasoline. The truck is driven primarly as to/from work vehicle, 70 hwy miles round trip weekdays.
The engine runs smooth on idle, but has recently began to repeatedly hesitate or miss "under load", such on acceleration, or pulling a hill.
Any suggestions as to what the problem might be? Thanks.

 

I had a similar problem. found out my coil tower was corroded from electrolysis. couldn't tell until I took wire off and noticed the white powder all around. then after scraping it found it was pitted. changed the coil with msd
and no problems since. just a thought.

 

I had trouble just recently with mine - ran fine at idle, missed bad when accelerating. turned out to be plug wires, even though they were not very old - it pays to spend a little more for better wires. One way to check is run the vehicle in the dark and check under the hood for light blue sparks jumping from the wires to the engine. It might help to get the area a little wet. mine looked like a lightning storm under there. chek around the coil too. I had a broken plug wire and the increased resistance from that wire made the spark jump from the coil to the engine.

 

You could also check for trouble codes, see www.fordfuelinjection.com under getting trouble codes.

 

First guess would be plug wires,new doesn't meen good.I've seen alot of melted wires on these year trucks due to bad routing.Also worth checking for any codes if you can't find any thing obvious like mike L suggested.

 

Thanks to all for the replies.
I replaced the Dist cap, rotor and plug wires. Seems to have helped. Will find out more when I drive it to work tonite. Some long hills between here and there.
A question about plug wire routing. Is there a (postable) diagram to show how it should be? Thanks

 

Don't know if there's anything on paper as far as routing go's.Just keep away from anything "HOT", as much as possible.

 

Here's where I'm at now. Replaced Plugs and air/fuel filters in June. Truck ran fine all summer. Recently (about a month ago) began to "buck" on acceleration or under load, such as going uphill. Runs smooth at idle. In the last 3 weeks, I've replaced rotor, dist. cap, plug wires, and today the coil. And I'm still at square ONE. In fact it's getting worse.
HELP!

 

Just a thought, my truck does the same thing, I'm not sure if the engine is actually missing or if it is "tranny shudder", when I get on the gas, and the tranny downshifts my miss goes away.

 

I've thought of that. My truck has the manual Mazda 5 speed overdive that uses automatic tranny fluid. I'll check my fluid level today.

 

Tranny fluid checks full. So now I seem to be left w/the possibility of a fuel problem.
I suppose the only months old filter could be clogged. Or it might be that the Fuel pump is going out. Or maybe injectors. What would your guess be?