I have a 97 f150 4.2,130k... While crusing at highway speeds(90-115km) and on back roads going up small hills and slight inclines my truck studders/missfires, If I stomp on the gas it clears up, but once I get back to crusing speeds the studder/missfire comes back. While driving intown truck runs smooth. It has new plugs,wires,fuel filter,cleaned MAF & IAC valve,fuel presure checks out too, also ran some good injector cleaner and the problem still occurs and is gettting worse. Could this be a bad coil pack ? I priced one out and its $240 from the local dealership. Has anyone else had a similar issue ? please let me know if you have any suggestions as this is getting expensive.. by the way no codes or engine light comes on ..
how old is the transmission fluid? if it has not been changed you might have converter shudder problem. that normally happens at highway speeds, constant throttle.
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2001 SuperCrew 4 x 4 5.4 XLT - 190,000 miles
2002 Explorer 4 x 4 4.0 XLT - 120,000 miles
Well for one i wouldn't give that much for the coil pack try a local oreillys and you can get one a lot cheaper and i think coil pack sounds like a pretty good chance is it throwing any codes ??
My engine light came on today, After a month of dealing with this missfire I finally got a code P0304(missfire on cyl 4). I guess I'll have to pull the plug and wires on that cyl to double check them, any other ideas to solve this P0304 code?
On a brighter note I hope this rules out it being the transmission, It was rebuilt about 30 000 km ago at a heafty $2000 bill. Not wanting to do that again anytime soon lol
If it was a bad coil pack could it have set off the P0304 code ?
"if i stomp on the gas it clears up". normally that steers you away from the ignition system, but if you got the 304 code, then you got a problem there. that code shows up when it stumbles on #4 cylinder. it could be the plug, could be the coil, and could be a plugged injector. plug is an easy change and less cost. how about pulling #3 and #4 plugs and looking at them? see if #4 has any visual problem. switch #3 and #4 and see what happens. if code continues son #4, then i would consider the coil.
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2001 SuperCrew 4 x 4 5.4 XLT - 190,000 miles
2002 Explorer 4 x 4 4.0 XLT - 120,000 miles
Changine plugs on these engines in a royal PITA so I wouldn't do only #4. I'd swap all 4 plugs on Bank 1 and the #4 COP. Pulling the fuel rail makes getting the COPs and plugs out manageable. Install new "O" rings(2 per injector). The "O" rings cost about 2 for a dollar. Put some oil on the new "O" rings before you install them. You can use the parts swap method, but it's so much work getting the plugs and COPs out it's not worth the extra work of removing and installing them a second time to correct a problem you didn't fix the first time.
The studder is missfire due to inability to fire lean mixtures under the specific conditions of light throttle and light engine load in that speed range.
Here is why:
At these conditions, the EGR is opened, timing advanced and fuel is cut back making the mixture very lean by intent and design, in the PCM program.
If the ignition can't fire the plugs under these lean conditions, a miss results until you apply more throttle.
At higher throttle openings, the EGR closes and everything is restored to normal with a richer mixture that the ignition can fire without a problem.
Usually it is a coil on COP motors but can happen to other configurations when there is a marginal ignition fault.
If you can make it happen and it follows the above action, you have that issue.
It only takes one cylinder to cause a problem like this
Changine plugs on these engines in a royal PITA so I wouldn't do only #4. I'd swap all 4 plugs on Bank 1 and the #4 COP. Pulling the fuel rail makes getting the COPs and plugs out manageable. Install new "O" rings(2 per injector). The "O" rings cost about 2 for a dollar. Put some oil on the new "O" rings before you install them. You can use the parts swap method, but it's so much work getting the plugs and COPs out it's not worth the extra work of removing and installing them a second time to correct a problem you didn't fix the first time.
The 4.2L doesn't have COP's,and there's no need to pull the rail to change the plugs.
JL
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