Try some Hyper Fuel in the gas. My truck was smoking like crazy with a cold start and when i put in some Hyper Fuel in the gas, it has completely stopped smoking. Got it at Oreilly's, and I can't believe the difference it has made, engine is running much better and the gas mileage is up.

 

The truck still shutters and misfires on cold starts. The ect sensor was replaced and fuel pressure was checked. Neither has brought me any closer to making this thing sound healthy when cold started. Cylinder 8 misfire code is surfacing on a weekly basis.This is what has been done so far: plenum fix, new cat and o2 sensor, fairly new plugs, wires, cap and rotor, wires routed per TSB, cleaned throttle body and related sensors. What could be going on?

 

Having similar problem,but no smoke. Best I can say is take it somewhere that can do a thorough diagnosis. You know#8 is the problem. But it could be partially burned valve, sunken valve seating and metal expanding after warming up. Valve springs lose lose tension after 100,000 miles , which can cause misfiring and rough idle. These are only opinions I got from two shops I paid to figure it out. So am going to try one more time

 

Have you done a compression test on this motor? If so what were the numbers. If you have not done one it's time to do one wet and dry.

 

Compression test was done with numbers between 140 and 150 dry (wet was not done)

 

Next would be a leakdown test on that cylinder to see if air is escaping through exhaust valve, when it should be closed, I believe. What I don't get is if it is bad valve, would compression be that good,140 dry? Any feed back would help me and GreenEH out, thanks guys.

 

Leakdown test will help...... consider that when the engine is running, cylinder pressures are WAY over that 140 PSI you see on the compression test....

 

Wouldn't compression be lower than 140psi if you had burnt or poorly seating valve on just number 8, and causing a misfire? One explanation I got was my #8 exhaust valve was hammered or sunken into head and after it warms up it expands and then seals better, thats why the idle smooths out after it gets to operating temp. Sorry, didn't mean to hijack your thread OP. Your problem is the closest I could find on here after hours of reading, minus the smoke out the tail.

 

Codes on even cylinders are common. I have misses on 2-4-6-8 I think the wires on that side are causing it by touching, which seems to be a big problem with this engine.

 

Readram, ask away with your questions. The discussion does no harm to this thread as it appears we have similar problems. About the smoke out of the tail pipe, aside from the usual vapour that comes out on cold starts in the morning, the black smoke no longer is an issue (unsure if it ever was an issue, was going off of a friend's observation). What I can say is that it seems the issue temporarily goes away IF i change out #8's spark plug for a new one. She will cold start for a week or two just fine then comes the rough idling, missing, and stumbling once again. The plugs themselves look fine; they aren't wet or black either. Fuel injector cleaner has been run through the system and all maintenance is up to par. I am starting to think running with a blown plenum for a prolonged period of time has done a number on cylinder 8's valves or head. Would the infamous cracked head due to a blown plenum cause these issues? Would a leak down test uncover this?