How to determine misfire on a cylinder

[erikofnorway]

My engine is suddenly running on 3 cylinders. What is the easiest way to determine which cylinder, and then narrow down where the problem lies?

Erik

[Ben Dover]

You can touch a grease marker to te sparkplugs while it is running, it will melt when in contact with the good cylinders. Shorting out each sparkplug wire will indicate the dead cylinder and will also indicate whether it is firing. If the wires are rubber insulated, just pull them off the plugs one at a time. You may have simply just fouled a plug, in that case it will be wet when removed.

[erikofnorway]

I pulled the plugs earlier and they were all sooted up, but none were wet. I have the spark plus wires from Ron, and tried to remove them while running and got zapped. So never was able to remove them. The engine suddenly runs rough and "uneven" and temp settles at 175 (vs 185 normally).

Erik

[tamnalan]

Erik, is it a steady miss or intermittent?

[artificer]

Could be as simple as attempting to do a proper tune as suggested with a cartwheel diagram in the TM rather than jumping from pillar to post.

[Tony W]

G,day Eric

I would give it a compression test.

Then if you have the tool a coolant pressure test.,

Coolant leaking into a cylinder can cause a miss, it can also cause your temp to rise.

Hope you havn,t blown a head gasket!!!!!

Good luck

Tony

[echelon1]

Artificer has it said.
Do a tune up and start from there.
Possible causes for a dead cylinder are sticky valves ( comes and goes ), leaky valves ( missing cylinder at idle but runs strong, regular poping noise at exhaust ), manifold leak close to a valve port ( only cylinder out at idle and iregular popping noise at exhaust, cause : broken manifold that might only show when the manifold is removed) , ignition issue. ( faulty spark plug, faulty dist cap, faulty spark plug lead, repro rain caps, humidity inside distributor.)
Blown head gasket, the issue is most present when the engine is hot.
Always start with a tune up and rule out the simple things.
Most can be determined with a vacuum gauge, but one need to be experienced.

Gindi

[erikofnorway]

Thanks for all the good pointers! I found that the choke was stuck partly on as choke cable has come loose. This is probably why lugs were sooted, and possibly the reason engine was running rough, sounding like it ran on 3 cylinders. I will let you know if this was the cause, but I think it is.

Erik

[Wolfman]

Back to figuring out which cylinder is missing.
Take the plug wires out of the cap one at a time instead of pulling the wire off the plug.
Keeps you from getting ZAPPED ! I hate it when my eyes glow in the dark.
If the wires are tight as you said, pull them loose and stick them loosely in the holes before you start the engine.
Makes life a lot easier.

[fernando mendes]

Years ago I had a misfire/lack of power in my L134 engine.It is very difficult to identify in which cylinder is.I checked all four valve tappet clearances and discovered that the [b]exhaust valve adjusting screw of the fourth cylinder[/b] was always too open although I adjusted with 0.014" hours before.I corrected using a special paste for metal.

[bazza46]

The way to short out a plug and not get zapped is this.
Use a screwdriver with a plastic handle. Touch the point of the screwdriver to the head, somewhere near the plug, but not so near that the spark jumps to the driver and zaps you before you can complete your circuit.

Then lean the shaft of the driver towards the terminal of the plug, making sure that the tip of the driver doesn't become separated from the head. As the shaft touches the terminal, the spark will take the first and easiest path to ground, not through you.

But make sure you aren't touching any of the metal part of the driver, as the spark will then divide and take the two paths of least resistance - the screwdriver tip and you.

[erikofnorway]

It appears that it was the choke. After reattaching the chocke, checking it for proper operation and replacing the plugs it again runs smoothly. I can see/smell no signs of contamination of the oil. It did not run very long with faulty choke adjustment. Thanks for all help.

Erik

[artificer]

Now go for a good run....not just around the block or down the super market....

[Oilleaker1]

Thought I'd add that the simple way to find a bad wire/plug while running is to clamp to the wires a inductive pickup timing light. If the plug is not jumping a spark or the cylinder is not firing, the light won't blink! Makes it a no brainer and I hate getting shocked. Ouch! John