How do I test coil with digital multimeter.

[Bob in Tennessee]

Pete and Hobo, I bypassed resistor and ran 12v direct to coil and spark was no better. The coil was getting hot so I shut her down and left her alone for a couple of days. I went fishing in the Tennessee river yesterday and me and a buddy of mine filled the livewell with Blue's and Channel cats. The biggest weighed nine pounds. I dug out my mulimeter but I've never learned to test for resistance. Took off my 12v square can and hooked leads to top and spiral wire, put it on 20k ohms and registered nothing. Moved leads to top of coil and front distibutor cap contact and got 10.4, am I in the right direction.
Thanks

 

[Bob]

"am I in the right direction."

NO!

"hooked leads to top and spiral wire, put it on 20k ohms and registered nothing"

By NOTHING, do you mean "zero Ohms", or "infinity"? (It HAS at lest SOME continuity there, or it wouldn't be overheating.)

The primary winding, which is between those terminals SHOULD have a resistance of 1.5 to perhaps 3 Ohms (depending upon whether it is "original 6-Volt", or some version of a "so-called 12-Volt coil".

"Moved leads to top of coil and front distibutor cap contact and got 10.4"

10.4 WHAT... Ohms, K Ohms, Meg Ohms?????

At BEST, testing a coil with an Ohmmeter is nearly MEANINGLESS, unless it shows a "dead short" or an "open".

A single sorted turn in the windings will hardly affect the Ohms readings at all, but will greatly reduce spark intensity by dispating energy as heat, rather than spark.

A coil tester functions by measuring how the coil "rings". Any shorts will greatly reduce "ringing", and cause the tester to "flunk" the coil.

 

[Bob in Tennessee]

Thanks Bob. Right now I'm grasping at straws. My spark won't jump 1/8, much less 3/8, and I haven't stumbled across the solution yet, even with all the help I'm getting from this board. The coil I referred to is one of those aftermarket, black, squarecans that fit on top of the distributor, and it is labeled 12v. I am running the hot from the switch, to a resistor, then to the coil. I have bypassed the resitor and it makes no difference in the spark. That's why I'm suspicious of the coil.

 

[Bob]

The coil LIKELY is bad.

Try replacing it with a new one, with the appropriate resistor to limit non-running primary current into the 3 to 4 Amp range.

APPARENTLY, the OEM resistor/terminal block is a GOOD match to many of the "so-called" "12-Volt coils being sold today.

 

[Pete Cowart]

So you had much better luck fishing than getting #4 to fire. Good for you, it often helps to step away from a problem for awhile. I know I'm going backwards again but I don't remember you posting this. One of the first posts I saw was that you had "totally gone though the engine". Correct? Now, what was the reason you went through the engine? Was it missing on #4 before? Not running completely? Just trying to help find some direction.

Pete

 

[Hobo,NC]

Nuttin else i can add,,, Bobs got ya covered,,, your coil can not deliver a Knock out punch,,, it needs a knock out punch to git the engine running,,, the coil needs to have the ability to deliver a knock out punch under different operating conditions,,, thats why how far a gap it can jump and continue to jump a wide gap is more important than the color of the spark,,, A coil does not work any harder than it has to,,, a weak coil can beat the best mechanic if he's only look'n for spark

 

[Bob in Tennessee]

No Pete, I didn't go back throughthe engine. I just re-lapped the valves, and checked tappet clearance. My compression is good and Hobo and Dunk don't think it is an internal problem. Bob thinks it's the coil, so tomorrow, it's TSC again. Dell say's to use the OEM resistor but this tractor didn't have one on it so I have an aftermarket. The spark is still very weak. 1-2-3 are firing but sooting up the plugs, and #4 is getting weak spark and no fire, even after bypassing resistor with 12v from switch to coil.

 

[WhiskyDog]

last year one of the neighbors here, had a problem like that no fire to #4 . the distributor cap had no connection in the cap for #4. The wire hole was blank. took him awhile to figure it out.

 

[Pete Cowart]

According to the TSC website it's their part number 0236588, $34.72.

good luck,

Pete

 

[Dell (WA)]

Bob.........yer squarecan ignition coil is technically an "auto-transformer", meaning ALL the coil windings are electrically continuous. This means with one ohm-meter lead connected to the top terminal, you should read continuity to either and both of the bottom terminals. (the springy-thingy and tab) and you should also read continuity between the springy-thing and the tab.

Current specifications of the modern 12-volt squarecan ignition coil call for about 2.5-ohms between top terminal and springy-thingy. Make certain iff'n not auto-range, yer digital ohm-meter is on LOW-RANGE, other wize, the digital HIGH-RANGE readout will tell you NO-OHMS (zero-ohms) between the top and bottom. (its a technical thing) which indicates a SHORT.

Iff'n yer fancy-spancy digital ohm-meter has a LOW-RANGE and you measure and you measure between the top terminal and the tab, the digital readout will indicate INFINITY or OPEN CIRCUIT. (no sparkies) This ain't necessarily true. The correct specification for the secondary is about 6800-ohms.

This is why you can't really tell much about enny sparkie coil with ohm-meter.

But my "calibrated" sparkie tester ALWAYS tells the truth. Just take enny ol'sparkie and bend the side electrode out for full 3/16" gap. Then clamp the metal shell to continent metal bracket. Plug enny sparkie wire to top of calibrated tester. Now with ignition ON, crank yer starter motor so engine turns. Do the sparkies jump the 3/16" gap with blue-snott authority or are they weak wimpy yellowish-orangish? See how eazy that is?

For reference purposes, my eazy starting 6-volt 52-8N sparkies will jump a full 3/8" gap ......Dell, yer self-appointed sparkie-meister and former electronics calibration lab ENGINEER (retired)

 

[Phil (NJ,Az,Sask)]

(quoted from post at 15:27:37 05/10/08) Pete and Hobo, I bypassed resistor and ran 12v direct to coil and spark was no better.

Bob,
It sounds like your Condensor may be Bad or not making good Contact
Use an Old one & make sure you have a good Ground etc.