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Discussion Starter #1
I have a 5.2L 318 -Magnum V8, added 2qts of oil yesterday unknowingly, I bought one can of 10W-30 and the other was straight 30W. Truck ran fine for about 40 miles. On my return home it started to shudder and the check engine light finally came on as I was pulling in the drive. I took the truck to Advance Auto parts to have the light read which stated miss fire #8 cylinder.
Would you think that the thicker oil I added was part of that problem? I drained the oil and replaced the PCV since I already had it at home but the truck is still running rough. I’m thinking a bad plug, maybe wire or injector. I’m gonna run some sea foam through it on my way home tonight to see if cleaning it helps then pull the plugs and see if they’re fouled with oil.
Hoping its not a “dead” cylinder…any thoughts or experiences that you may have had? I checked online and diagnosis goes from as simple as changing the plugs to replace the engine.
 

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I hit send too soon, My 360 did the same thing one time it was the plug cracked. But at about 245K it ended up being a valve after some heavy towing. I got the same trouble code mis fire on cylinder.
If you do a comperssion test and the problem cylinder is lower than the others add some oil to it theough the plug hole. If the comperssion goes up it is a bad ring, it is stays the same most likley a valve.
 

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It isNot the oil, check the simple stuff first, plug, wire etc.
 

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Discussion Starter #6
Pulled #8 plug last night, it was nasty black with sludge build up, you couldn't even see the electode. Replaced all plugs, changed oil and filter again, ran sea foam in the crank case and gas tank. Noticed some somke from the tail pipe when I get on it. Hoping that's just from the carbon build up and the sea foam doing its thing.
 

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The 318& 360 magnum had a problem with the bottom of the intake gasket leaking and sucking up oil vapor form the lifter valley. Dodge had a TSB issued on the problem.
You can test by putting a vac gage on hose on the driverside that goes to the air cleaner and plug the PVC valve cover port on passanger side . Then have someone start the truck and see if the the gage pull vacume ( you have a leak) it should build pressure.
 

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Could be that plenum gasket as stated above, if your burning oil and mileage is lacking that may be it, if your up over 100000 chances are it's leaking slightly anyway(poor design from the factory). Hughes engines makes a fix for it (120 bucks). Mine did that (burning oil, fouling plugs) ended up clogging the cat...plenum fix took care of the problem
 
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