2006 F-150 Random Cylinder Misfire

Tiny
MIEC
  • MEMBER
  • 2006 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 90,000 MILES
I keep getting P0300 codes for random cylinder misfire. I have also gotten cylinder 2, 4 & 7 misfire codes. The misfire can be observed while sitting in park and accelerating slightly above idle or it can be observed while accelerating hard under load such as climbing a hill.

What I have done so far is the following:
Replaced all plugs and coil packs.
Replaced fuel filter.
Replaced fuel pump driver module.
Checked vacuum (holds steady at 18" of Hg). Looked/tested for leaks and found none.
Verified there is plenty of air entering the throttle body.
Cleaned the mass air flow sensor.
Inspected for any loose wiring to coil packs and injectors and none found.
Inspected vacuum while accelerating to approx. 2000 rpm and vacuum held and increased slightly so I don't believe there is exhaust blocked. I also don't see any glowing catalytic converts.

Perplexed as to what could be the problem or what to do next.
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Thursday, April 14th, 2016 AT 8:11 AM

7 Replies

Tiny
HMAC300
  • EXPERT
These are a b--ch to find even for a pro. Best way is for a pro to freeze frame and go through and see if voltages are ok on sensors because it can be any sensor causing problem. You can check fuel pressure with a gauge auto parts rent it and test compression but normally not a compression problem
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Thursday, April 14th, 2016 AT 9:32 AM
Tiny
MIEC
  • MEMBER
Thanks for the reply. I don't have diagnostic equip to check the freeze frame of mode 6 data. There is no Schrader value or other good location on the fuel rail to check the fuel pressure. I just replaced the fuel pump driver module which regulates the pressure and the misfire is the same. I could check the compression but my understanding is if the vacuum is adequate and steady, typically the vehicle is mechanically sound. The vehicle does run fine besides these intermittent misfires. I also don't have any way other than a resistance test to check the injectors, but it seems a bit unlikely that I would have multiple bad injectors? Also resistance checks are not always very help. I guess just as unlikely that the new plugs and coil packs I installed would have multiple ones defective. If I were to go to a shop and ask for diagnostics, how would I phrase my request so as to get the results I need?
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Thursday, April 14th, 2016 AT 10:57 AM
Tiny
HMAC300
  • EXPERT
Most of the cheap scanners at auto parts have freeze frame capability you don't need mode 6 for that to get your results tell them you have amisfire and what you have done. They will freeze frame it i'm sure
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Thursday, April 14th, 2016 AT 12:07 PM
Tiny
MIEC
  • MEMBER
I have a scanner that will provide freeze frame and live data. That is how I got the misfire codes. What other info do you want me to look at?
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Thursday, April 14th, 2016 AT 12:13 PM
Tiny
HMAC300
  • EXPERT
You have to look at all the sensors to see which one either has low voltage to it or not giving correct voltage on output sometimes it's the maf sensor. I can't go through all of that if you reply with voltages.
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Thursday, April 14th, 2016 AT 12:47 PM
Tiny
MIEC
  • MEMBER
Certainly not all sensors contribute to the misfire. I could see the 02 Sensors and the MAF sensor, but that is about it. I have checked those and they are good.
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Friday, April 15th, 2016 AT 6:16 AM
Tiny
HMAC300
  • EXPERT
Do what I said in very first reply I don't think you checked everything.
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Friday, April 15th, 2016 AT 6:46 AM

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