Cascade Crew

91RSVert · Posted: Tue May 28, 2013 5:06 pm Post subject: Spark plug wire question....

So I went to start hunting for a missfire today. Not having any tools to test that kinda spark except a timing light, I used it to find one wire not flashing at all.

Now I'm questioning....
I the plug is bad, will it still flash? Or if no flash, it means the issue is the wire/before the wire?

Also, does anyone know of any type of heat resistant loom I could run the wires thru?

chevymad · Posted: Tue May 28, 2013 5:13 pm Post subject:

If the plug is completely grounded or shorted out it won't flash because it will never build up a high enough voltage.

You can buy woven fiberglass boots that go about 8" up the wire from the plug. There is also heat resistant wraps, but you'll need to take the boot off one end to put it on. Both are kind of expensive, so if at all possible good looms are usually cheaper. I usually use a good loom but still end up using 1 of the heat boots and each side. This is on my 70 truck, the car looms up really well without the boots.

aaron_sK · Posted: Tue May 28, 2013 5:35 pm Post subject:

chevymad · Posted: Tue May 28, 2013 5:44 pm Post subject:

If this is on his truck he may need 2 of the boots. My truck's headers had 2 wires that the tube went right over the top of. With regular plugs the boot would only be maybe 1/8 to 3/16 away from the tube. Wouldnt touch but after a few weeks the boots would dry up and crack.

91RSVert · Posted: Tue May 28, 2013 6:05 pm Post subject:

It is on the jimmy. On the right rear, I forgot to tye wrap one back and it burnt.

However, the wire in question is on the left middle #3. I changed the wire out with another I had laying around. It now blinks on occasion, but still not as often as the others. Confused

:edit: also, what do you call good loom. That plastic stuff for putting wires in is melting and its still 2-3" away from the manifold.

chevymad · Posted: Tue May 28, 2013 6:12 pm Post subject:

Don't trust a timing light to check spark. Inductive pickups arent the most accurate way to test.

Low compression will also cause weak voltage on a wire. Since it takes a higher voltage to jump a gap in a compressed gas then it does at normal pressure.

Ignition voltage will increase until it reaches the point it can either jump the plug gap or cross the point of least resistance. If you ever have access to a scope and put it on the coil wire, you can see the voltage go very high when a plug wire is either bad or disconnected. You'll also see voltage very low if the wire or plug is shorted, or if the cylinder has no compression.

91RSVert · Posted: Tue May 28, 2013 6:17 pm Post subject:

the only tool I know I have access to is the timing light. I know dad has a few gadgets, but I have no clue what they are called Laughing

However, if I get what your saying. If there is debris, fubared gap, completely carboned up plug, my timing light method could be giving me false readings?

The truck ran grate last night, and this morning. I doubt it could have fubared compression that fast.

aaron_sK · Posted: Tue May 28, 2013 6:17 pm Post subject:

Does your Dad have a spark light you can throw on it?

91RSVert · Posted: Tue May 28, 2013 6:18 pm Post subject:

91RSVert · Posted: Tue May 28, 2013 6:24 pm Post subject:

chevymad, i google searched "coil wire scope". What I saw come up picture wise, we do not have.

Twilightoptics · Posted: Tue May 28, 2013 8:22 pm Post subject:

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_22989180-P_x_x?cm_mmc=ACQ-_-Google-_-enhancedRM-_-22989180&ci_src=17588969&ci_sku=22989180&ci_gpa=pla&ci_kw=&gclid=CNyHyNC7urcCFYiDQgodC10ANg#utm_source=acq&utm_medium=google&utm_campaign=enhancedrm&utm_content=22989180

91RSVert · Posted: Wed May 29, 2013 3:55 am Post subject:

Yes, I got one of them a few years ago. I dunno where I put it. Dont remember moving that into my tool box, but I might have. Will hunt tonight for it.

aaron_sK · Posted: Wed May 29, 2013 7:38 am Post subject:

Just buy a new one. HF sells them for like three bucks. Razz

I've had mine for years, very handy bottom-of-the-box tool.

91RSVert · Posted: Wed May 29, 2013 5:39 pm Post subject:

HF is about 45min away from me. I have an oriellys thats about 5min away.

Anyway, new cap and rotor botton, and swapped the one sp wire. All are lighting up the same now. I think I need to pull the plugs and possibly clean them. It still doesnt run like it did on the one trip. But alteast all are saying its firing now.