When spark plug wires go bad....

[Orlando_87GN]

I was messing with the car today (hybrid) and it wouldn't run for crap. Did the usual blips while idling and reving it up in park usually resulted in a stall. Car was undriveable, barely got it back in the garage from a short trip to the store. So in my usual thrash of replacing parts and checking all my harness connections I started to get really frustrated when nothing was helping. I changed the crank sensor first because I saw spikes in the RPM via DS and PL. Problem persists so I changed the coil/module, ESC, ECM, chip, checked the cam sensor, disconnected my Dakota Digital Tach adapter, got rid of some spade connectors under the dash, replaced all my relays under the hood, provided the ECM with an external 12v from a jump box and basically pulled my hair out all day. After each change it was the same thing. Car would barely run.

Then I changed the plug wires to a different set (nice used ones) that was given to me because I figured the problem isn't the wiring, it's got to be interference of some type. Sure as $hit, problem solved.

Now what in the world would cause a spark plug wire to completely screw up the whole car? What should I expect if I ohm these out or what happens to them when they go bad?

I am lucky I figured it out, I was getting ready to push the car out in the street with the keys in it. Unbelievable that a plug wire could cause such a waste of time.

[87natty]

I've heard of plugs wires crossfiring and jumping signals, etc. Usually it's when they contact metal (valve cover, etc) or overlap each other a certain way. I think the shielding inside breaks down and they almost arc, but without an arc, if you can picture that. I remember a shop teacher telling us about a guy who just changed his wires and the car wouldn't run.

[The Radius Kid]

I would say a break in the core conductor on one wire.
That's a nice source of RFI and weak spark to the cylinder.
Did you have any spark leaking to ground from any of the boots?

[The Radius Kid]

Originally Posted by 87natty

I've heard of plugs wires crossfiring and jumping signals, etc. Usually it's when they contact metal (valve cover, etc) or overlap each other a certain way. I think the shielding inside breaks down and they almost arc, but without an arc, if you can picture that. I remember a shop teacher telling us about a guy who just changed his wires and the car wouldn't run.

You can get inductive cross fire.
For the naysayers,I PROVED IT in an impromptue parking lot demo one night[you should have seen their faces!].
What happened was a friend had a Cavalier with a 2.2 in it and one of the wires had been replaced due to a boot being pulled off.
His car didn't seem to run *quite* as well as he would like.
The bad wire was still in the harness and another one run next to it.
The bare end was just hanging there,so with the engine running,I pushed the bad end down towards a bracket on the engine........................[remember this wire was NOT connected on either end].
A spark jumped the gap to ground[the bracket].
It just goes to show you.

[87natty]

Originally Posted by The Radius Kid

I would say a break in the core conductor on one wire.
That's a nice source of RFI...

THAT'S the term I forgot. You can do a resistance test on the wires to check them, right? I did cylinder balance tests by using vacuum hose between the (Chevy) distributor cap and plug wires, then grounded out each cylinder by tapping the vacuum hose to a ground while watching an RPM gauge.

Did your radio pick up any noise Mike? Like a winding sound?

[The Radius Kid]

Originally Posted by 87natty

THAT'S the term I forgot. You can do a resistance test on the wires to check them, right? I did cylinder balance tests by using vacuum hose between the (Chevy) distributor cap and plug wires, then grounded out each cylinder by tapping the vacuum hose to a ground while watching an RPM gauge.

Did your radio pick up any noise Mike? Like a winding sound?

The best test is to slip an inductive pickup from a timing light around the wire just above the boot,while the engine is running.
Watch for consistent spark flashes.
Resistance measurements can be misleading because the internal core can be compromised in one spot along the wire and still show decent conductivity[ohms].
Spark transmission produces heat stressing the wire's conductor much more strongly than a volt/ohm tester.
That's where the timing light tells you what's going on.

[Orlando_87GN]

That is the thing. The radio gave no clue to a spark plug wire problems.

[99ssconv]

Rule of thumb for spark plug wire resistance is 1,000 ohms per foot.

[Black Car]

Originally Posted by 99ssconv

Rule of thumb for spark plug wire resistance is 1,000 ohms per foot.

This isn't correct for Jascob's blue wire. 100 ohm per foot. When any mine get above 200 ohm, I usually have a mis.
Best way to test is with Casper coil/ign/wire tester.

Gary

[turbofabricator]

Another good rule of thumb, on turbo cars, is just replace them every year. Cheap way to insure they are in good shape. Keep them (old ones-yr old) in your trunk for the odd chance of failure and you have something to throw at it. Plugs and wires are usually the FIRST things to go bad. If you are having prolems, change them FIRST. I've been were you are, so I'm speaking from experience. I'll bet you won't do that again. Just another learning curve you tackled.