Dead Cylinder?

[Danny Joe]

I was out driving yesterday, my motor developed a bad miss, one cylinder not firing.

Pulled the plugs, #1 slightly fouled (blackened). Pulled all plugs and performed pressure check, all cylinders between 130-140 psi (#1 was lowest at 130, all others 135-140).

Spark at each plug, even #1 was same as the others.

Swapped plugs with #2, same as before, driving around for a few minutes blackens that plug in #1 also, and the one from #1 fires in #2.

I tried something someone on this forum suggested: Increased idle speed, unplugged wires, no change when #1 was unplugged. When I plug it back in, it has a good arc between wire and plug.

Replaced points, condenser, distributor cap and rotary button, no change.

If a cylinder has good compression then that means that valve adjustment, valves, pushrods and lifters are all working properly aren't they?

I guess my next step will be to get a plug wire to test with.

[Danny Joe]

I guess my question is, could a cylinder have a bad lifter or pushrod and still have good compression?

Any additional info/opinions are welcome.

[bbodie52]

I was thinking the same thing. But if the intake or exhaust valve never opens, you might see good compression but still have an inactive cylinder. Removing the valve cover and observing the valve train action may reveal the problem.

[Jerry Whitt]

You noted the plug turns black. Black usually means excess fuel.

This leads to thought of carburetor problem.

Which engine? How many carburetors?

[bbodie52]

If it were a carburetor problem, wouldn't all of the cylinders on that side be affected in the same way? But what if the exhaust valve on number one was not opening (as with a bent push rod). Fuel/air mixture would continue to be drawn in to the cylinder, but could not be exhausted since the exhaust valve would remain closed. The result might be a build-up of fuel vapor that would not ignite properly and would foul the spark plug.

[Danny Joe]

OK, I've been in denial. Since making my last post I have accepted that I will have to do that, Brad.

Jerry, it is a 64 turbo, but all the other plugs are good, so I am leaning toward Brad's diagnosis.

I was hoping somebody would come up with something else besides bent push rod or collapsed lifter, hate something like this happening to a freshly rebuilt motor. It hasn't knocked or made any other unusual noises, it just started missing while driving.

Oh well, now I have to pull the valve cover on that side and check it out. (sigh)

[miniman82]

Something that hasn't been mentioned yet: the Corvair cylinder head can suffer from excessive carbon deposits in the log style intake manifold, this can be especially bad with the 150/180 engines if the carbon seal on the turbo is bad meaning tons of oil is being passed to the engine. Even if it's not blowing smoke right now, that doesn't mean it hasn't happened in the past and been repaired. So it's best to pull the intake crossover (easy to do), and shine a light and small mirror in there to see what you can see. If that doesn't turn up anything, I'd say you probably have either a collapsed lifter, bent pushrod, or stuck valve on that cylinder.

If you do find a bad head, you may as well drop the power pack and do both. It will give you a chance to replace the exhaust valves, do some basic porting, and install new guide seals to ward off any future oil deposits that would keep you from enjoying your turbocharged ride.

[miniman82]

Here's a pic from 'that other forum':

http://corvaircenter.com/phorum/read.ph ... 604,211616" onclick="window.open(this.href);return false;

[flat6_musik]

My guess is that you may have an oil fouling problem on that cylinder, or your spark is arcing out from the plug wire somewhere on the top fan shroud or somewhere else. Re-do your compression check and make double sure you've dumped out all the pressure from the compression gauge before you go on to the next cylinder. If you've got compression and a fresh plug, that thing should fire.

[Danny Joe]

Hi Miniman.

The PO had the engine rebuilt and the turbo sent to Clark's for rebuild. There was, however, no mention of any head work being done. Parts listed included ring kit, oil pump kit, rod and crank bearings and turbo assembly. No lifters, valve springs, valves or pushrods listed.

If it will warm up a little today I am going to try to pull the valve cover and check it out. We had 8+ inches of snow Wednesday night, it still hasn't melted yet. It is only supposed to get up to 36 today, and I don't have an enclosed space, just a carport. Snow in Alabama sucks, we aren't prepared for it.

I just had another thought. A few days ago I posted about my cylinder head temperature dropping suddenly while driving. I thought then that possibly the oil cooler had been plugged up with crud and it broke loose. Now I wonder if some of that crud could have found its way into a lifter?

[bbodie52]

From what I remember, it is more difficult to make a spark under pressure than it is in normal atmospheric pressure. A spark displayed between the spark plug wire and ground may still not fire properly at the spark plug under combustion chamber pressures. A carbon track or crack in the distributor cap, or a faulty spark plug wire could conceivably be causing a misfire on number one. That is the only other possibility I could think of that would be restricted to a single cylinder — especially after you have swapped out the number one cylinder spark plug. Since you said you have already replaced the cap and rotor, a misfiring plug wire is all that would be left on the ignition side. The fuel system seems to be ruled out since only one cylinder is affected, and cylinder compression is good. The valve train seems to be all that is left.

Good luck as you continue troubleshooting to determine the cause of this engine fault.

[Danny Joe]

Brad, I found and tried another plug wire, no help.

[Danny Joe]

I just read the description of the lubrication system in the shop manual, the oil goes from the filter to the cooler, then to the rest of the engine.

This means that if a good slug of crud broke loose from the oil cooler, it would have gone directly to the moving parts!

This is what I have to deal with today!

[tiger13]

If you have spark that will jump from the wire to the plug, your wire is good. You can eliminate that issue. Same as if you held the wire off of a good ground source and got a good spark from the suspect wire, you can eliminate it from your list of suspects. The same can be said about your points cap and rotor. You have changed out the plug itself to a different cylinder and gotten the same results, the plug worked in another cylinder, so that plug is good.
You will not get compression if your valve train is not functioning, you've got to have valves working to allow incoming air into the cylinders for the piston to compress. IF you watched your compression gauge, did you see it pump up in stages as the engine turned over? Meaning, you said it had 130 psi in the suspect cylinder, it did not jump right up to 130 psi on the first revolution, it most likely took 2-3 turns of the engine to get there. See what I mean? you could "see" your valve train working as the compression built up to 130 psi. Of course with the engine running it does that instantly, but at the slow cranking speed it takes a couple revolutions to accomplish this.
If the exhaust valve was somehow damaged to prevent it from opening, the engine would still be drawing an air/fuel mixture into the cylinder, and getting spark to it and igniting it at the proper time. BUT it would have no way to vent to exhaust gasses out, so when the intake valve opened again, it "should" pop back through the carburetor on the side where the dead cylinder is, as that would be the only available exit for the burned gases to exit. The original poster did not comment on any strange engine noises, that the engine made, just that the engine developed a "dead" cylinder. It may be possible to tell more with a cylinder leak down test. Or it very well could be do to a carburetion issue.
Right now it APPEARS the engine has spark, compression, but does it have fuel?

[1949chevy]

Almost sounds like a intake manifold problem on the dead cylinder.....

[Melb-Mike]

Best way to know what is going on inside would be to look inside. How ? Well they make some pretty nifty cameras with small snake like leads. I bought one recently from Dell City Wire which has a Wi-Fi view on your ipad or iphone. Ipad is ideal since the screen view is bigger. Cost of the camera shipped was $127. This camera will go into the spark plug hole, or the intake manifold without removing the carb and it has its own LED light to boot. Takes the mystery out of what is happening. Just a thought.

You could have a lifter that is collapsing at running rpm but holds at slow or cranking speed. This would explain getting an OK CR test but yet the engine has a miss. I assume you are running the stock ignition, points or pertronix module and NOT the Crane XR-700. The reason why I say this is I had an issue with the Crane module messing up when the PO had a full 12 VDC going to the coil rather than the mandatory 7 VDC. It seemed that #1 cylinder suffered the failure. It would idle OK but not great, but had a terrible miss at mid RPM. It took me a while to find it.