Misfire/Not shifting at high acceleration high load

dsmith

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Hi Everyone,

I am having an issue with acceleration. If I accelerate normally it shifts and sounds fine. If I stomp on it however, it revs high, won’t shift out of 2nd or 3rd, makes a weird non consistent ticking sound, and the check engine light starts blinking.
Code just keeps saying Severe Misfire on Cyl. 5

I just changed all plugs and coils with OEM parts prior to this. I bought ANOTHER new spark plug to replace the one in cyl. 5 (thinking it was a bad off the shelf plug), did nothing. Swapped coils on 5 and 6, still nothing, tried a new fuel injector on 5, nothing. Tested Fuel Pressure while driving under load, that was fine. Checked the bore with scope for anything odd and didn’t see anything.

I’m at a loss now and am not sure where to look next. Any help would be greatly appreciated!
 

Trainmaster

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Some might suggest you do a leakdown and test on the cylinder to make sure you don't have a valve train problem. Or remove the valve cover to check the follower and cam. I'd check the wiring to the coil first to be absolutely sure it's not still a miss.

On a long shot, check the plug on the computer too. A bad computer can do this too.
 

Allie Cooper

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This might be a long shot, but my 03 F-150 started doing the same thing a couple of years ago. It wasn't bad at first, mostly happening going up steep hills, but got increasingly worse. After reading the codes and trying to diagnose it myself, then asking advice from several mechanics, it eventually got so bad it was almost undrivable and barely made it to the shop. The mechanic there is really good and had it diagnosed the next day - a clogged catalytic converter. I installed a new set of cats and it has run perfectly ever since.
 
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dsmith

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Some might suggest you do a leakdown and test on the cylinder to make sure you don't have a valve train problem. Or remove the valve cover to check the follower and cam. I'd check the wiring to the coil first to be absolutely sure it's not still a miss.

On a long shot, check the plug on the computer too. A bad computer can do this too.
I’m planning on taking it to my buddies shop soon to do a leak down test. I tested the resistance and voltage to the wires and both were good. I tried a new pigtail and that didn’t help at all. I’m thinking maybe a broken follower or something so it’s looking like I’ll be digging into it even further soon.
 
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dsmith

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This might be a long shot, but my 03 F-150 started doing the same thing a couple of years ago. It wasn't bad at first, mostly happening going up steep hills, but got increasingly worse. After reading the codes and trying to diagnose it myself, then asking advice from several mechanics, it eventually got so bad it was almost undrivable and barely made it to the shop. The mechanic there is really good and had it diagnosed the next day - a clogged catalytic converter. I installed a new set of cats and it has run perfectly ever since.
That’s crossed my mind too! But I’m playing process of elimination with cheaper parts still at this point. I’m hoping it’s not the cats cuz I’m not looking to spend that much on this pile. Thanks for the suggestion, hopefully I’ll have a solution soon
 

Motorcity muscle

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Any strange noises while driving the truck? My '07 made what we thought was a slipping belt squeal, it was the cat plugging up and ended up whistling before we figured it out.
 

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