Help fixing a dead cylinder

[Dr J]

The number 6 cylinder on my car is much cooler than the rest. For comparison I put a thermocouple on the exhaust manifold for cylinders 4-6 and got the following:

#4- 294 C (561 F)
#5- 268 C (514 F)
#6- 189 C (372 F)

The measurements were taken with the engine warm but the car idling.

This is what I have done:

1) Compression tests run at 120 +- 2 psi for all cylinders (I have about 8:1 compression due to thicker cylinder base gasket). Performed with engine warm.

2) Leak down test- all about 10% with engine cold

3) Tested for spark, cable, and coil (I have electromotive hpx) - ignition looks OK and I have a spark

4) Fuel - tested a different line to a different location in the fuel distributor. Also switched fuel line to injector and injector. Finally put the injector in a cup and pressed on the bottom of the fuel injector and have fuel.

What should be my next item to check? rockers?

[HawgRyder]

When you tested for spark...was it with compression on the plug or out in open air?
In open air...a 30K spark will jump across the gap easily.
When compressed in a cylinder....30K can do the job...provided that there is enough current in the wire.
I have seen this type of problem on many occasions.
The plug may be bad...or the wire....or a leak accross the dist cap or down the insulator of the spark plug.
Try a new plug...and a new wire to see if it cures the problem...if so...by all means...replace all plugs and wires so that this does not happen with another cylinder.
Bob

[Dr J]

For the visual spark test the plug was outside but I tested a used working spark plug in the cylinder. Also switched cables for #5 and #6. Since in have wasted spark I also connected the wire to the other terminal in the coil. Same results.

[HawgRyder]

With compression test even across the 6 cylinders...it looks like the valves...timing and gap should be OK.
Is this fed by a plenum type intake?
Is it possible that you have an air leak in the #6 runner?
Or...worse still...a possible crack in the runner going to that cylinder?
I see you are supercharged...this will make the whole problem harder to find.
The manifold should distribute the charge of air evenly to each cylinder...but any obstruction in the system will cause an imbalance.
If the system is older than 4-5 years....perhaps the inside of the rubber connectors might have deteriorated or "bulged out" creating a "step" or crevace.
Bob

[Dr J]

The plenum is essentially a metal copy of the plastic airbox. The supercharger is currently removed so it is operating normally aspirated for now. The rubber connectors are a few years old but don't look bad. The #6 runner is hard to get at. I checked one of the nuts connecting it to the cylinder and it was tight. The other one is nearly impossible to check. I'll try to devise a way to check the runner and connection to the cylinder.

[Bob Kontak]

Originally Posted by Dr J

The #6 runner is hard to get at. I checked one of the nuts connecting it to the cylinder and it was tight. The other one is nearly impossible to check.

Carb cleaner on number six (head/runner) connection, runner and boot sounds like a real good place to spray looking for air leaks. Don't forget the injector.