2004 - 2008 F-150

Misfires while backing up

Old 05-21-2019, 07:13 PM
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Misfires while backing up

So I have a 2006 F150 5.4 FX4 constantly getting misfire coils A & F I've changed the spark plugs all eight of them and all 8 coil packs the truck will run fine one minute and then misfire for a few seconds often when I put the truck in reverse. Im lost please help
Old 05-21-2019, 07:35 PM
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There has to be codes or ones that are at minimal in "pending" status.
Old 05-22-2019, 10:44 AM
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Your mentioning coil designation by alpha letters "A" and "F" tells me you are talking about codes P0351 and P0356. Those codes are "electrical" in nature and occur prior to 'ignition'. What I mean is they are NOT misfires. There is something electrical that is 'preventing' normal ignition. Typical examples are broken COP primary clips that the rubber 'o'ring in the clip pushes back and interrupts good contact. That is a 'Primary Circuit Fault' and the plug couldn't fire if the PCM wanted to. That code will occur with 'Secondary' coil faults. Such as corroded or poor connection to COP spring or Spring <> Plug cap, OR something like plug gap TOO wide and the plug literally not spark.

In absence of the above failures, the PCM literally monitors the slight acceleration in crankshaft rotational speed immediately after commanding a spark. If it doesn't see that it knows the fuel-air mixture did not 'explode' -- THAT is a misfire, ie: P0301 through P0308.

Focus on electrical connections that could be effected by reverse some how.

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