2004 - 2008 F-150

08 4.2 misfire

 
  #1  
Old 02-23-2019, 07:26 PM
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08 4.2 misfire

i have an 08 with the 4.2 and it is running rough at idle and has backfires while driving. Replaced the coil pack yesterday and didnít help except for the check engine light going off. Had it scan before the coil pack swap and it showed a misfire on every cylinder. Any ideas on what else besides plugs? Has 110,000 miles on it.
 
  #2  
Old 02-23-2019, 09:35 PM
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If that's 110k on the original plugs, that's your problem right there. Could also be plug wires.
 
  #3  
Old 02-23-2019, 10:47 PM
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These have about 60k on them and I have them to replace but the last time it acted like this the coil pack was bad. This one didnít look bad after I pulled it off. Iím showing codes 300 through 305. Plugs are very hard to get too. Ford place replaced them the first time as a courtesy for something else.
 
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Old 02-24-2019, 12:18 AM
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Original plug wires? Replace them.
 
  #5  
Old 02-24-2019, 12:23 AM
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Replaced those with the coil pack 2 years ago
 
  #6  
Old 02-24-2019, 03:27 AM
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Which brand are you using for your tune-up parts? If you are using inexpensive coil pack, wires, and plugs......those could all be a problem. Did you use dielectric grease?

Ford MotorCraft OEM spark plug wire set is 7mm, which was good enough to leave the factory with. There are wires with thicker gauge. I don't know if they are any better. May not do anything special, except for work without failure. But anytime you try to save a few dollars with something less expensive, it never works out well. Some manufacturers offer a spark plug wire set specific to the F-150 4.2, which is what you want as opposed to generic wires. Look for 8mm wires, numbered for each cylinder so that you don't have to figure it out, and think about the reputation of the seller. Are you buying Taylor wires, or "made in China, sold on eBay"?

The coil pack should be Motorcraft. Not that Motorcraft doesn't have issues. Motorcraft ignition coil packs are known to eventually fail with misfires, otherwise we would never have to replace them. A lot of people like Denso, since Denso is the OEM. I'm using a MSD, which is working without issue so far, only because of pricing and availability. There are over a dozen inexpensive ignition coil packs selling for $10 - $20, and none of them work well. Depending on where & when you buy it, the Denso & Ford Motorcraft could be $75 - $100, but at least they work.

Everyone says that you should only use Motorcraft spark plugs. There are other brands. And almost surely, the less you spend, the worse it gets. Some have had good results with Denso & NGK. I'm currently using E3, without issue. On some of the V8 & V10 engines where the spark plugs were breaking, Champion offered an alternative spark plug.

If starting off fresh with new tune-up parts does not solve your problem, then there is something else going on.
 

Last edited by Fifty150; 02-24-2019 at 03:29 AM.
  #7  
Old 02-24-2019, 03:31 AM
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All motorcraft. All I will use
 
  #8  
Old 02-24-2019, 03:42 AM
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Suck

Bang

and

Blow

You need air, fuel,and spark. Any issues with fuel delivery? Fuel pump, fuel filter, fuel injectors? Check your air delivery. Any obstructions? Is your filter clean? How about the intake from the filter housing to the throttle body? Are any of the sensors damaged or failing? Is the throttle body dirty? Also, check for compression.

Or you using cheap gas?
 
  #9  
Old 02-24-2019, 04:16 AM
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No cheap gas. I had to do a second tune up on my old chevelle after 2 weeks due to bad gas. Cleaned the throttle body about 2 months ago and not noticed anything with sensors or anything. Air filter isn’t dirty I keep a check on that regularly and haven’t noticed fuel injector problems
 
  #10  
Old 02-24-2019, 05:34 PM
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Check cylinders for compression. Maybe use diagnostic software, datalog a test drive, and see what's happening as per all of your sensors.
 
  #11  
Old 02-24-2019, 05:46 PM
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Wouldn't hurt to throw a bottle of Techron in the gas to clean the injectors.
 
  #12  
Old 02-24-2019, 08:33 PM
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Kind of reminds me of this post...
https://www.f150online.com/forums/v6...ough-idle.html
 
  #13  
Old 03-07-2019, 11:48 AM
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Alright changed the plugs wires and coil pack. Still have a rough idle and loses power going up a hill. Plus takes more rpms to get to a shift point. Going to swap the coil pack for the old one that looked good and exchange the new one to see if that helps
 
  #14  
Old 03-07-2019, 01:58 PM
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Rough idle and loses power? Get your cats checked for blockage. Put Techron in the gas to clean the injectors. Replace the fuel filter. Do a compression test.
 
  #15  
Old 03-07-2019, 02:29 PM
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A few 4.2s over the years have worn the keyway on the harmonic balancer and changed the timing. Might be worth checking.
 

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