Newbie question: how do we check all cylinders are firing.

[Anjizkit]

Have a 1987 911 targa. Everything is great but I was reading one of the builds where the owner figured out that one of his cylinders was not firing.

Question is. How do we figure that out? Do we like hear for knocking? Do we do the stethoscope methods? What do we do?

Apologies if it’s already discussed.


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[al lkosmal]

Use your timing light by connecting to each spark plug wire, one at a time

[targa72e]

I have used a laser thermometer to check each exhaust pipe. If one is not firing (or firing at the wrong time because plug wires were mixed) you will see a lower temperature.

john

[PeteKz]

Why do you think they are not all firing?

[Mike80911]

You could also use a test light to ground each wire. Connect a test light to ground then stick the probe through the top of the wire where it goes into the cap. If the cylinder is firing the idle will drop.

[pmax]

A thermal scanner would be the perfect tool for this, hands off, no mucking with spark plugs etc.

[Dr J]

Get a squirt bottle that can send a stream rather than a mist and aim at each exhaust header, one at a time, noting how quickly the water evaporates. The one that does not evaporate quickly is the dead cylinder.

[Flat6pac]

+1 on DrJ. I use the windex spray bottle.
Bruce

[Anjizkit]

Originally Posted by PeteKz

Why do you think they are not all firing?

I am sure mine is great. The engine and smooth and pulls strong. But i was wondering how do we check this. So asked.


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[Anjizkit]

Cool answers. Thank you. I learnt something new today.


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[dtxscott]

Simply unplug each spark plug one at a time with the engine running. If the idle stumbles or changes, that cylinder is functioning

If the idle is unchanged when pulling the plug wire, that cylinder is no bueno.

[mike sampsel]

Originally Posted by al lkosmal

use your timing light by connecting to each spark plug wire, one at a time

+ 1

[pampadori]

How i do it:
I plug in my laptop to my ECM and open InfinityTuner software. While running, i deactivate each individual coil-on-plug one at a time to listen for the change in idle. Sometimes I deactivate each injector instead. :P

But same could be achieved by unconnecting each sparkplug wire one at a time.

[Anjizkit]

Am gonna learn what is a timing light now.


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[Superman]

Originally Posted by dtxscott

Simply unplug each spark plug one at a time with the engine running. If the idle stumbles or changes, that cylinder is functioning

If the idle is unchanged when pulling the plug wire, that cylinder is no bueno.

I strongly recommend against this. Experiencing 30,000 volts is an interesting experience. It teaches you to never touch the ignition system of a running engine.

The timing light method is a good one. As is the infrared thermometer method. Every tool box should have both these tools.

[pmax]

Along that vein, I was just about to mention the instant phase transition of water.

[Superman]

Yup. If you want to burn yourself really good with hot water, turn it to steam.

Fun Fact: Harkening to the days of steam shovels and other steam-powered equipment, the logo for the International Union of Operating Engineers is a steam pressure gauge with the needle pointing to 420.

[spoke]

A follow up to the OP's question of how to find a cylinder which is missing. I had a similar experience where the engine would run fine then just start missing a bit. It would run good for a second then miss, good, miss. Or miss a lot.

Looks like the issue I had was the plug wire plug socket was cracked and maybe or maybe not making contact with the plug. Not sure how testing would find this.

BTW, these are Beru wires installed about 8 years ago. Almost every one was cracked and 2 just fell apart when slightly stressed. Which plug wires would you suggest to replace?

[al lkosmal]

I have been using Clewett Engineering spark plug cables....they are very good/high quality

[wrxnofx]

Originally Posted by Superman

I strongly recommend against this. Experiencing 30,000 volts is an interesting experience. It teaches you to never touch the ignition system of a running engine.

The timing light method is a good one. As is the infrared thermometer method. Every tool box should have both these tools.

Meh, I've done it plenty and not ever had an issue.

Curious about the timing light method. How does that method insure the cylinder is firing? All a timing light tells you is that there is an ignition pulse being sent down the wire. It's not actually telling you if the plug is firing. Similarly, it's not telling you if the injector is dead. Both of these are possibilities that a timing light won't show.

An IR thermometer/camera is probably best.