check for spark at working end of plugs

[WmWatt]

I want to check the spark plugs for spark. I remove the plug, connect to spark plug wire, hold against metal to ground.
I use remote starter to crank engine. Does the key have to be in the igniton and turned to "ON"?
If so what prevents the engine from starting up? Happened just now. Interesting noise from open spark plug hole.
Thanks.

[zoe60]

Seems you would have to have the key on. You could screw another spark plug in the hole while testing. It is an amazingly loud noise, isn't it. A plug came out while I was driving an old Cutlass Supreme years ago. Scared me!

[scitzz]

Key on, if it starts, it starts.

Often, if by myself, I just stretch the plug wire someplace I can see it from the drivers seat, and use the key.

[Movin]

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_22983650-P_x_x?cm_mmc=ACQ-_-Google-_-enhancedRM-_-22983650&ci_src=17588969&ci_sku=22983650&ci_gpa=pla&ci_kw=&gclid=COfyqv7q4rgCFUrZQgodJE4AKg#utm_source=acq&utm_medium=google&utm_campaign=enhancedrm&utm_content=22983650

Why would you test like that?? You will get results that will mislead you. When a cylinder compresses the charge the voltage required to fire the charge will typically be about 5 times greater than the voltage required to fire the gap using the method you described.

To properly test the circuit you will need around .650 thousands gap just to see if the circuit can fire a .040 gap spark plug that is installed in the engine. I don't want to explain resistor plugs and the effects of fuel molecules near the plug gap. I typically use a .750 gap for testing and if the engine runs I do not call it done until the engine has run for a while firing this gap. The coils can warm up and break down, I want to know that. While all this is going on it is a good idea to run a ground all around the wire , cap and coil to see if any other path to ground is present. Using a spark plug to test for spark just tells you that the system to the coil is working, NOT that it is capable of firing under load.

Spark testing can be incredibly entertaining , have fun!!

[lessersivad]

Testing for spark can be interesting for sure.

Approx. 20 years ago I had an S10 Blazer that died on the way home from work. Got it towed home and proceeded to check it out.

At the initial start of diagnosis I had all the makings of a running engine. Fuel, compression, and spark or so I thought.

Testing for spark with the alleged "tried and true" method of holding the plug to ground while cranking produced a blue spark. "Good to go" was my thought at the time.

I dinked around with that Blazer for quite a few days and still no start.

I FINALLY bought one of these;

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_ignition-tester-calibrated-for-hei-ignitions-kd-tools_22981200-p

Lo and behold, no spark thru tester. After checking for pulse to the coil I replaced the coil and I had a functional vehicle again.

I also bought a "small engine" version of the same tester (smaller gap) for mowers, chainsaws and such.

These have saved me a bunch a grief over the years.

Also I have found with the HEI tester I don't always have to see the spark as I can actually hear it "snap".

[Bert]

Princess Auto sells an inexpensive spark tester with lamp inside and male and female ends for hook up on high tension wires. If spark across plugs is strong the light flash within the tester is strong and if weak the light is weak. These devices are sold as ignition spark testers (ie do you have current in the wires) but in fact have proven most useful to check spark plugs. If all I get is a weak flash I replace the plug. I've never tried this on a car engine yet but for small engines (lawn mowers/snow blowers/chainsaws) the device works like a charm and most of my buddies have run out to buy one after they see how well it works.

[WmWatt]

Bert: I've seen those in Utube videos and think they're neat but I don't think they tell you about the condition of the spark plug, just the current in the wire? One video shows the plug out and grounded and the spark not jumping the gap but off to the side of the electrode instead inidcating the gap is too wide. Seems you get more information looking at the action at the working end of the plug itself.

They also show a home made tester where you cut off the tab part of the gap of an old plug and ground the plug but I'm not sure what that's supposed to tell.

[Bert]

Bert: I've seen those in Utube videos and think they're neat but I don't think they tell you about the condition of the spark plug, just the current in the wire?

I was introduced to this $12? tester via a small engine course at Algonquin College. The prof couldn't have done a better job of advertising/promotion for these things! Many of the project engines that were tested, that showed a faint light flash, yielded easy starts (and strong light flash) once that plug was replaced. Cracked, soiled or oily plugs wouldn't generate a flash at all. Really nice; the device flashes strong enough in daylight to be seen easily and ostensibly to confirm current or lack of but at the same time (because it's in line and the still-installed plug is part of the circuit) does tell you much more. If you specifically want to test a plug (and you already know the wires are good) then swap in a new and properly gapped one for comparison! Can't get much simpler than that.

[Movin]

The oscilloscope of old provides a visual track of both current and voltage....how high the in voltage is the up and down track, duration or volume of current is shown by how far across the screen the spark travels before the fire goes out. The exact shape of the entire event would tell us if the coil is healthy, the plug gap normal, dirty or worn out. Bad wires are easy to spot. Lots of other variations all easy to read.

The RFI generated by the ignition varies depending if the plug is shorted down the insulator or partially by deposits or firing normally. The testers that straddle the wire or are plugged in both blip a light that varies depending on how high the voltage goes. A slow dull blip would indeed show the condition of the plug to be fouled or shorted. A robust blip is all well. A short quick blip would indicate too much gap to fire either in the wire or the plug.

These testers are not the same as spark gap testers. The spark gap testers have proven more valuable as they stress test an ignition system to find problems that causing a miss only 50 miles away on some really big pass. Or they find problems that have no symptoms yet.

Really, you want both types of testers and others hanging on the wall...

[WmWatt]

I now have one of those testers. Could only find one outlet who carries them so spent the whole morning riding my bicycle to the other end of town and back to buy one. They had the one that lights up for $6 and two kinds that just spark but have an adjustable gap for $10 each. I got the one that lights up. Thanks for the suggestion.

BW for those who own Festivas like me because they are cheap, allow me recommend the economic and health benefits of a bicycle.