Flooding # 7 cylinder

[mojavered]

I am having some trouble with the # 7 cylinder (440) not firing.  The cylinder is flooding.  I have ran a compression check, all cylinders were the same with the exception of that one being down 30 psi.  I squirted 10 cc of oil in spark plug hole and ran compression test and compression was back up.  I have ensured that there is spark in that plug.  Changed all plugs.  I have changed around plug wires to make sure that there was nothing wrong in that wire.  I pulled the air bleeders out and the idle bleeder on the rear drivers side was clogged.  Cleared, tried again, still not firing.  Pulled valve cover and appears that rockers are moving up and down the same amount on all.  Pulled carb off and adjusted the butterflies so that they are all showing a small (square sized) gap in the transition way.  Set all fuel mixture screws the same.  Idles well.  I have not checked to see if maybe a valve is sticking, I guess that will be next.  What can I try next?  Thanks!

[Chryco Psycho]

long shot but is the vacuum line to the brake booster attached into the runner to #7 cylinder ?
If so plug the port & see if ti fires , I have seen a leak into the brake booster cause the cylinder to go lean to the point where it will not fire & the plug fouls

[72cudamaan]

Not sure whats happening but I wouldn't suspect the valves.  Your compression was down probably due to fuel wash on the cylinder, as adding oil put the #s back to normal.Maybe the spark is weak?  Might try changing cap and rotor.  What are the numbers from the compression test?

[Supercuda]

Here's the left-field possibility: This is also a symptom of a bad or out-of-phase reluctor wheel in the stock-style electronic distributor.

[mojavered]

Vacuum line is from booster to the rear of carb.  It is a proform 950 and there is only that one 3/8" port coming out.  I did change the cap, not the rotor.  I have a brand new one I can throw on there real quick.  What is the reluctor and can I check it? 

[moper]

You were down 30psi. there's a mechanical problem with the ring seal or valve sealing. Do a leakdown test and it will tell you which one...

[cjm]

If the compression increases after a wet compression test, this is sign of worn rings (or the rings not seating).......

[72cudamaan]

If the compression increases after a wet compression test, this is sign of worn rings (or the rings not seating).......

 I was assuming that fuel was entering the cylinder and not combusting. This would lead to washing the oil off of the cylinder, thus loss of ring seal. When oil was introduced back into the cylinder, the compression went back to a normal range. So it would seem that ignition to that cylinder is suspect.

[cjm]

Yes, but he did state that he verified spark, although after the compression test... he "could" have flooded that cylinder initially but after changing the plugs (and wires) the fuel would have evaporated and #7 should be firing.......(Movared) --Did you verify spark at the plug (ruling out the diz cap).......    Note: If compression increases after a "wet" test it is normally related to the rings. If it were a valve, there would be no increase in compression during a wet test.....   My "guess" is that it is either a worn ring or a ring stuck in its land...   Sometimes some Marvel mystery oil can free up a "stuck" ring....    Good Luck....

[cjm]

Also, try another regular (dry) compression test on that cylinder.... see if it drops back down again....   

[mojavered]

I took it down to a mechanic so they could throw it on a scope.  They said that all cylinders were firing just fine.  When I got home, I checked the temp at that header tube and it was 177 and the rest were between 205 and 290.  I know there is going to be some fluctuation since it is not direct port, but...
If it were a worn ring, would'nt I be burning some oil? 
I am still at work and will not have time until Thursday to check everything again.  So it is sitting and I will run a compression test on that cylider and a couple others to get a baseline, first thing. 

[Aussie Challenger]

If there is a cylinder down, pull the oil filler cap and see if there is excess blow-by. Another possibility could be a worn valve guide, they don't always make a noise.   

[moper]

A broken ring is more likely. You might burn oil, you might not. It might just misfire once in a while, or it might have missed once ina  while and it gets worse... The end result is it's hurt and I would say the safe bet is to assume it needs rings at minimum, if possible.

[mojavered]

I was thinking that the compression test was low on all cylinders with a 118-120.  On the # 7 cylinder, it was a 90.  I was thinking I should be more in the 135-150 region?  Does it make a difference with lift and duration?  My lift with 1.6 rockers is .504/.504 with duration of 228/235. 
When I do get home and check the compression, what could I assume if #7 has the same compression as the rest of them?  I just want everything to be ok and am in denial that a ring is bad and am trying to find anything to point to something else.

[cjm]

I would agree with moper, it is related to your rings on #7....   Like you said, test the compression again...  If the results on #7 are within the same range as the other cylinders -- the original problem could have been that the ring was "stuck" on its land (temporarily) and is now freed up....