Random Miss

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May 30, 2013 | 07:48 PM

SquirrelCutter

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From: Republic of Texas

Random Miss

Or at least that is what the auto parts babe said when she plugged her reader into my truck to define the Check Engine Light being on.

2007 F250SD-XL, 120K miles, 5.4L gas motor. I've noticed when I set the cruise control and roll along as soon as I hit a noticeable grade the tranny kicks down a couple of gears and the engine stumbles. CEL blinks but when the ground levels out again all is good. Just going up a hill, and only on cruise as far as I have noticed.

One of my mechs thinks I have a bad ignition coil, the other thinks I need a new catalytic converter. The second one is nuts, I figure, but the coil could be.

What say ye asspurts?

Pic of my tailgate. I pulled it off my F150 because the one that came with this truck is wasted:

When I go redneck, I don't jack around

Jun 24, 2013 | 03:49 PM

pswann64

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Gr8 tailgate man! Also note that you hail from the great state of Texas, i'm in north Texas, DFW area. When u c that cel blinking it means your damaging the environmental controls on your truck, specifically the twin cats on the exhaust system, one each side. DTC code for a random miss is PO300, then 1-8 for specific cylinder. My 05 SD 5.4L,3v, codes PO 306 and i've tried everything short of getting into the timing to eliminate it, to no avail. I've checked for vacuum leaks, swapped all the plugs out with motorcraft, moved COP's, bought a new COP for cyl #6, watched how much anti-seize i apply to plug and still cant resolve the misfire. I've heard/read stories about interference causing random misfires on the 5.4's but cant figure mine out. Maybe someone else will chime in and get us on the right track. post back with results if u run it done am curious about it.

Jun 24, 2013 | 09:35 PM

stoffer

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which cylinder?

Jun 24, 2013 | 10:41 PM

SquirrelCutter

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From: Republic of Texas

I dunno. The gal at O'Reilly's that scanned it told me all it said was "random miss."

I'll have another sample, I'm sure, soon because I am about to take the Gray Whale back out on the road for a week of camping and drunken revelry next week.

Jun 24, 2013 | 10:42 PM

SquirrelCutter

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From: Republic of Texas

pswann64, I am up in Garland.

Jun 25, 2013 | 06:31 AM

pswann64

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Your not far from me then. Back to your truck, if you read the manual the flashing cel means damage to the emission components. From experiance I can tell you it will take out the cats. New y-pipe and cats will run you about $385.00 for the direct fit replacement plus 4 o2 sensors @ $40.00 each, best price I've found with me swapping them out. Anyway your annoying miss will lead to other damage if not resolved and other things to have to diagnose. I have a mid grade scanner ($130) I use to at least help me isolate the general area and then clear the code. unfortunanly my #6 cylinder is still causing a miss, even after new motorcraft plug and COP pack. I'm going to try swapping the injector for that cylinder with another one and see if my miss moves. If it does then simple deal with installing a new injector, if not then it's something else, i.e timing chain slipped a gear or some other demon. Good luck with yours and let us know if you find the issue. Patrick

Jun 25, 2013 | 03:25 PM

SquirrelCutter

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From: Republic of Texas

What is COP?

Injector sounds like a possibility. Since it only happens rarely the timing is definitely not the issue. I'll find out next week, big road trip coming up, I'll see how it behaves.

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Jun 25, 2013 | 04:19 PM

pswann64

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Hey SC, COP is acronym for the "coil on plug" ignition system our trucks have. Old shool was one coil feeding x number of cylinders-new school is one coil per plug. You say your going to drive it on a big road trip, are you still getting flashing check engine light on it or did babe at auto store clear the code and it hasen't returned? I'm being redundant with that question because if the cel is flashing and you continue to run it that way you will destroy the catalytic convertors on it and when you have to replace them then your going to drop some fold.

I know this from personal experiance on my 05 truck. Someone else may chime in and correct me but i dont think it would pop a code for bad cats, you'll just start building backpressure and your milage/economy will drop. I wrk on all my own stuff but price everything, Cats from dealer =$1K, cats at muffler shop=$800, do it myself parts are +/- $365 for eastern y-pipe and cats plus another $160 for the oxygen sensors in front of and behind convertors. Do as you please just trying to give you the benefit of my own mistakes.