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Discussion Starter #1
I have updated all the ignition with accell wires, autolite plugs and a NAPA copper cap and rotor and still have an annoying problem. Whent he truck is up to temp 190F it will miss when I accelerate. On the freeway at 50mph it seems to get worse. Once I hit cruising speed of 70mph I let up on the throttle and it smooths out. I have checked the codes and none are present. Fuel trims seems to be very close to zero while driving and long term fule trims are right on zero. I have a feeling my coil is the culprit because the missing starts at about 30% engine load. Driving in the city ( <35mph) there is no miss or its very slight. Any ideas?

Mods Installed:
Cat back system with a flowmaster street muffler
Spacer plate (not much in performance)
Spectre cold air package
Royal Purple oil only for my Ram
Autolite 3923 plugs gapped at .040
Accel 8mm plug wires

Thanks
 

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What is it acting like when it misses? That's odd that it isn't throwing a code? Hmm you have yourself a head scratcher lol
 

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Discussion Starter #3
5.9l Missing on acceleration

What is it acting like when it misses? That's odd that it isn't throwing a code? Hmm you have yourself a head scratcher lol
The only time I did "force" a code was flooring the truck to WOT. The miss seemed to be really bad at that point and did not feel like it was on one cylinder. The check engine light came on flashing yellow, like the truck was saying "what the heck are you doing to me" I let up on the throttle and the light went off. Using OBD Wiz I did get a P0308, miss on cylinder 8. I went out and checked the injector on 8 by starting the truck and physically moving it to see if I had a vacuum leak or a fuel leak. It was tight with no gas leaking. The plug is brand new (two weeks at best, I broke the electrode out changing the spark plug wires). Other than that, at idle when warm there is a slight miss. It stutters a little off idle also. The research I have done shows it might be a coil breaking down. I just wanted to get some advice before buying a coil and finding out its something else.
 

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i would pull ur spark plugs and look at them and go from there up to the wires, coils etc. just double check everything
 

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Ahh, the dreaded Cyl 8 miss fire. That means its time to change your plenum gasket if you have not done so yet. That sounds like what your problem is. And if you broke anything installing the plugs and wires. You NEED to fix that problem asap. but I would put money on it being the plenum gasket. Take your air intake off and open the butterflies on your throttle body, (while its not running) and look into there with a flashlight. If you can see any oil or oil residue or anything, then you need to change the gasket. You might also need to replace your Cat if this problem has been going on for too long.
 

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Discussion Starter #6
Thanks, I will take a look at the plugs. It is possible one is out of tolerance (or More). This is the firsxt mopar I have worked on with a computer so I am a little out of sorts. I am used to carbs and cam not electronics, but I want to learn how to tune this truck. I have found a method to test the coil so I will check it also. I will post back what I find if anything.
 

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Discussion Starter #7
5.9L missing on acceleration

Turns out it was a bad number eight plug. The insulator was cracked top to bottom and I had just replaced this plug. After putting in a new plug she runs fine now. thanks all
 

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how hard/expensive is that plenum gasket to change.my truck is missing some kind of terrible and i am looking at my cat being the issue, and mite be making my o2 sensor throw a code.but i do seem to burn around a quart of oil from oil change to oil change.could that plenum gasket be my problem?
 

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how hard/expensive is that plenum gasket to change.my truck is missing some kind of terrible and i am looking at my cat being the issue, and mite be making my o2 sensor throw a code.but i do seem to burn around a quart of oil from oil change to oil change.could that plenum gasket be my problem?
Its not bad. Its a matter of taking the intake off, and changing the gasket on the bottom of the intake. Its one of the easier problems to fix on these trucks. But you probably will need to change the o2 sensor and wouldn't hurt to change the cat also. I went with a magnaflow cat when I did mine.
 
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