Plug Wire & Coil Checking

"Snuffy "Hub Cap" McKinney" wrote in message news: snipped-for-privacy@earthlink.com... What's a good way to test plug wires and coil without buying new parts? Parts stores around here only sell full sets of wires. I guess I could get one from a junk yard but would still want to test it.

OBD2 shows cylinders 1 & 4 are misfiring. That's only when starting - after warming up runs smooth. Checking with ohmmeter, both wires are

=====

Gave up on the shade tree troubleshooting. Had it checked at a reliable mechanic. Compression was 1.2 - 1.3 on all plugs. Head gasket was not leaking. #1 plug, possibly other, was cracked. Replaced all plugs. Runs like a sewing machine. EGR was fine.

So much for T/S by internet and "brand name" shops. Don't know why OBD gave bad info.

"Snuffy "Hub Cap" McKinney" OBD2 shows cylinders 1 & 4 are misfiring. That's only when starting - after warming up runs smooth. Checking with ohmmeter, both wires are

=====

Gave up on the shade tree troubleshooting. Had it checked at a reliable mechanic. Compression was 1.2 - 1.3 on all plugs. Head gasket was not leaking. #1 plug, possibly other, was cracked. Replaced all plugs. Runs like a sewing machine. EGR was fine.

So much for T/S by internet and "brand name" shops. Don't know why OBD gave bad info.

OBD was correct.

One trick to nail bad wire is to look at them under hood in the dark when engine is running. Bad wire will cause mini fire work.

I can see it was right about the #1 and #4 misfires. Why was it correct about EGR having insuffient exhaust flow?

"Snuffy "Hub Cap" McKinney" <

I can see it was right about the #1 and #4 misfires. Why was it correct about EGR having insuffient exhaust flow?

You did not say anything about EGR codes, only misfiring!

Different thread :-)

I save some of the previous set of wires, in case my girlfriend's brother steals some of mine. But they're useful for testing too.

Even from one car to the next. I save the longest ones, plus a center one.

longer or shorter wire. The resistance should match length.

I once had a leaking head gasket according to the compression test. Two adjacent cylinders in a V-8 were low. Car ran fine for 3 or 4 more years. I think there's a difference between air escaping to the next cylinder at cranking speeds versus running speeds. Much harder at running speeds.

Although maybe if it were two diferent cylinders leaking hot exhaust stroke gas would have ignited input or compression stroke gas in the other cylinder. Can that happen?

Oh,yeah, that's right. Sorry about that!

- Oh,yeah, that's right. Sorry about that!

I noticed today there is still a miss at 40-50 mph. Low speed is smooth. Will check the codes again tomorrow....

"Snuffy "Hub Cap" McKinney"

- Oh,yeah, that's right. Sorry about that!

I noticed today there is still a miss at 40-50 mph. Low speed is smooth. Will check the codes again tomorrow....

It 'could' be a bad coil.. This happened on my '03 Buick.

It MAY give fireworks. If the insulator is leaking. If the conductor is open and the insulation is good you will see NOTHING.

Likely. With 2 bad plugs the vacuum is low and incosistent, causing low EGR flow. The cause was bad plugs, but the result was low flow. Knowing how emission controls work, and why, allowa a REAL mechanic to determine what the problem really is. a 1 and 4 miss will virtually NEVER be a head gasket..When there are multiple codes, you need to figure out what can cause what - bad mixtures and bad flows can be caused by misfires - and can also cause misfires - but generally not consistent localized misfires.

Fix the simple obvious stuff first and most often the "strange" stuff goes away as well.