coil resistance

[L.C.Gray]

I'm trying to get a machine started for the first time and can't seem to get any fire.

In checking the coil, should you be able to read resistance or continuity across the + and - terminals?

What about between the + or - and the high tension side?

I would think you should beable to get continuity betweeen the +/- terminals and between the - and HT unless the coil is open.

I have 2 coils, one off a running engine and one off an unknown and I can't decide whats what with them.

 

[Bob]

A typical "Kettering" ignition coil will have between 0.5 Ohm and 4 Ohms of resistance beteen it's primary terminals.

Typical secondary resistance will be in the 4000 Ohms to 10,000 Ohms range, measured from one of the primary terminals to the secondary connection in the "tower".

There will be a difference (equal to the primary resistance) in the secondary Ohms measurement, depending upon which primary terminal you measure it from, NOT enough to be significant, or likely even MEASUREABLE by all but "lab grade" equipment.

HOWEVER, just because the measured resistance seems on the OK range, it DOES NOT mean the coil will make a good spark. Even ONE shorted turn, which isn't even enough to noticeably affect the resistance reading will GREATLY reduce the spark output.

Also, a crack, or "carbon tracking" in the high-tension area will bleed off spark, but probably NOT show up as a change in winding resistance readings.

 

[Tom43]

Bob has a great response. An ohmeter will tell if a coil is bad. You must have both primary and secondary continuity; however these checks will not tell if a coil is good. When warm and under load the coil can arc both internally and externally. The only definitive test is an ignition scope, coil tester or substitution with a known good coil. Remember you MUST HAVE THE RIGHT COIL FOR THE APPLICATION.

 

[L.C.Gray]

Thanks y'all. I did check again and got comparable readings between the coil known to be good and the unknown one. I re-gapped the points and checked manually that it was actually firing the coil. I put fuel in, clicked power on and hit the switch and she fired right off first try.

Darn! Its so good to be so good!

Long live "Project: Orange Crush!"

 

[Bob]

"I checked manually that it was actually firing the coil."

How loud did the wife/gf SCREAM? Or, did you hold the coil wire yourself???

 

[ScottyHOMeY]

What are wives, gfs for?

Mine's real good for checkin' out mags.

Ain't sayin' she likes it, but she's as good as any meter and he ain't caught on yet!

 

[L.C.Gray]

I held the coil wire near the distributor body while opening and closing the points with a screwdriver. I didn't have anyone handy to hit the starter button for me.

Just split with the g/f last night..... she sure would have come in handy to hold that wire today.... oh well!

 

[Bob]

LOL!