Spark plug/wire tester

[chuckwagon101]

Is there a tester that you can clip to the spark plug wire to tell if it is firing at optimum performance?

Thanks, Chuck

 

[koda2000]

you test plug wires by measuring OHMs resistance with a VOM. you look for so much resistance per foot of wire, but if your plug wires have over 75k on them i suggest you just replace them.

edit: for typical plug wire you're looking for 10,000-15,000 OHMs per foot. if more that that, the wire is probably bad.

 

[deweyville65]

I do not know of a tool that will do that, but, the old school way is to pull a plug, or use a spare, ground it and observe the spark. My 96 will jump spark a good two inches at the coil. You don't have to ask how I found that out. Anyway, the plug should have a bright blue healthy spark.

 

[jremington59]

My wife bought me this little tool that looks like a pencil with a half moon end at one end and a light at the other. You lay the half moon end on the wire and the light pulsates with the spark. It doesn't tell you how good of spark, only if there is spark.

 

[BrooklynBay]

This tool will help find a break in a spark plug cable: http://www.northerntool.com/shop/to..._sku=9094058&gclid=CP2O2czEl7oCFUOe4AodylsAkQ

This tool is good for comparing the spark energy of each cable:

This tool is the best but the most expensive:

It has a digital display for reading the actual voltage of each cable.

 

[chuckwagon101]

Those tools look great!

I think I will replace the spark plug cables.

I just finished replacing the spark plugs but there is a "little bit" of a "miss" at times that I can definitely detect with just my own senses.

Question.....is it very difficult to replace those wires?

Just from looking...it seems like a lot of twists and turns around hidden parts!

Let me know.

PS....I am a "shade tree" mechanic.......

 

[BrooklynBay]

Did you check the gap on the plugs before you installed them? Which brand did you use?

 

[chuckwagon101]

I gapped the plugs to the book specs....I think it was 54 thousandths

The plugs were Autolite platinum

 

[BrooklynBay]

Those plugs are good. They are the same as the Motorcraft plugs.

 

[chuckwagon101]

Those plugs are good. They are the same as the Motorcraft plugs.

Thank you, that's good to know because I was beginning to wonder if I should have gone with Motorcraft.

Question....Why would I be getting a very slight "miss" at idle? Just a little "stumble" and not all the time.

I DID ruin the left front boot with a screwdriver getting it off but I cleaned and wrapped the torn place with black electrical tape.

I looked under the hood at night, total black in garage.....could not see any spark jumping from any of the boots.

 

[BrooklynBay]

The old cables might be going bad with a different amount of resistance on each one. Test each cable with an Ohmmeter, and compare them to a new set of cables. I'm sure that the old wires will vary in resistance, and be much higher than the new ones.

 

[chuckwagon101]

How difficult is it to replace those wires?

Will I need to remove components from the vehicle to do the job?

 

[BrooklynBay]

Some of them might be a little difficult to reach but it's not impossible.

 

[shucker1]

I have a 98 Explorer 5.0 that did the same thing after about 60K miles. Only did it for my wife and not me.
I thought she was nuts!

Brought it to the dealer finally, to keep the peace....

Tech found the problem and explained it as an "On Demand" Ignition system. The more you mash the gas the more spark the PCM puts out. She is a light driver, I'm heavy foot.
That is why I could never duplicate the problem.

Either way a new set of wires and the problem was gone.

 

[chuckwagon101]

I have a 98 Explorer 5.0 that did the same thing after about 60K miles. Only did it for my wife and not me.
I thought she was nuts!

Brought it to the dealer finally, to keep the peace....

Tech found the problem and explained it as an "On Demand" Ignition system. The more you mash the gas the more spark the PCM puts out. She is a light driver, I'm heavy foot.
That is why I could never duplicate the problem.

Either way a new set of wires and the problem was gone.

Thanks Shucker........looks like it's a new set of wires for me.

Question.....If it is tooooo difficult to run the wires in the same places that the other wires are located.........can I just re-route the new wires, leaving the old wires in their place. Maybe even clipping the old wires that are "easy" to get to.

Would this affect performance by having the wires run in a different route?

 

[BrooklynBay]

Get rid of the old cables & install the new cables the same way as the old cables.

 

[shucker1]

I agree with BrooklyBay. No need for all that old stuff hanging around. It just creates clutter.

I've also always used the practice of never running wires side by side on sequential firing cylinders.

Electro magnetic interference does some strange stuff.

That's just me though.

 

[Runnin'OnEmpty]

Just to add; you can also check sparkplugs with
an ohmmeter. If you probe the tower terminal and
the tip, you'll get a resistance reading. It's about
5-6K ohms on a good plug.

 

[1998Exp]

I have replaced several very bad cables, and all had perfect resistance. Not saying that deterioration of the conductor is impossible, but pinhole defects in the insulation appear to be a much more common source of trouble as it dries out and starts cracking after few years of service. Not easy to diagnose without an oscilloscope, unless the defects are big enough to create visible arcing. Swapping cables between cylinders will eliminate the coil and the plug as the culprit if you can see the misfire following the suspected cable. Replacing the set of cables every few years (3-5) seems to be a good preventive strategy.

The COP (coil on plug) system in newer vehicles eliminates the cable problem, but judging by the amount of postings about those on the other forum that I am following, it's definitely not a perfect solution either.

The old cables might be going bad with a different amount of resistance on each one. Test each cable with an Ohmmeter, and compare them to a new set of cables. I'm sure that the old wires will vary in resistance, and be much higher than the new ones.