I was reading in a another thread where someone was having problems with the engine running weird and someone said to replace the coil. Is there any way that I can check it using a voltmeter or ohm meter or any other test? In my endless effort to fix the rough idle, I am trying to eliminate the coil. I can't seem to figure out what's going on with this engine.
How can you check the coil?
Umfan92
1 - 20 of 28 Posts
Joined
·
401 Posts
I was reading in a another thread where someone was having problems with the engine running weird and someone said to replace the coil. Is there any way that I can check it using a voltmeter or ohm meter or any other test? In my endless effort to fix the rough idle, I am trying to eliminate the coil. I can't seem to figure out what's going on with this engine.
Joined
·
12,382 Posts
Two things come to mind, off hand.
1. You can test it for continuity and an OHM test. But, you'll need to know what Ohm reading you need to see. Someone, no doubt, chime in, But, you could Google for ideas.
2. If you connect your wiring in "reverse" on the terminals, the engine will start and run and you will not know the difference..........until you enter higher RPMs. At some point the engine will start to break down as a result of the reversed connections.
With rough idle, the coil is not the first thing I think of. The output quality is easily checked through grounding the cap lead and using a remote cranking switch with the ignition switch on.
Plug wire quality, (check at night and look for leaks) and looking for "tracking" within the cap are first. Second, check for manifold leaks and adjust the carb with a vac gauge, would be the next couple of tests.
Good Luck!
Joined
·
5,791 Posts
i always have a friend hold the cable disconnected from distributer . turn the engine over if he screams it's working ..
Joined
·
12,382 Posts
Also, check the color in his eyes. If "blue", the spark quality is perfect! LOL
Happy Motoring!
Joined
·
3,131 Posts
An ohm meter will show an open coil, but can't detect a shorted turn. A single shorted turn in a coil will kill the Q of the circuit, rendering it almost useless. However, an ohm meter test will reveal a resistance well within normal range for a shorted turn. If the coil is receiving proper voltage and the points gap is correct (and the capacitor is good), you should get a nice spark out of the coil. If you are getting a weak spark, a sub coil is the best test.
John
John
Joined
·
590 Posts
hahaha
irate:LOL! I guess this ends up being a new friend or a soon to be former friend.
Joined
·
401 Posts
Ok my friend screamed so it should be good. Lol Jk. Well I'm pretty sure the coil is fine but I still have a rough idle problem. I have a new Edelbrok 289 intake that someone gave me. I think I'm going to install that this weekend and rebuild the carb (even though it's new). And I'm going to change the fuel filter and make sure there are no vacuum leaks. Does anyone advise against changing the intake manifold?
Joined
·
12,382 Posts
Hi
With any intake manifold, the key is in the installation, not it's execution. Be sure to follow best practices, in sealing the front and rear block rails.
I would follow my tuning advice before tearing into a "new" carb.
Was this "rough" idle occur overnight? What are circumstances leading up to it?
Well I use a coil tester.
The only way to test a coil is with the tester. As pointed out you can not ever check a coil with meter as it is rare you will see a difference. Yes, failures do happen that could be found with a meter, but I could make a pile of bad coils that test fine to your one.
The coils usually fire good when cold. You let them heat up and the spark gets worse as they get warmer.
A coil tester is just a make and break circuit with an adjustable point gap. There is a switch to let current flow through the coil to let it warm up. The testers also allow you to test condensers.
The coil on my 65 failed during a parade one year. It ran fine for the first half of a mile parade. Then it started running rough and then just died. I let it cool and drove home. Put a tested good coil on and it has been fine since.
I have included a picture of some commercial units I own or have owned.
Here is a link a to a cheap way to build your own:
Model A Restorer's Club - Coil Tester
The only way to test a coil is with the tester. As pointed out you can not ever check a coil with meter as it is rare you will see a difference. Yes, failures do happen that could be found with a meter, but I could make a pile of bad coils that test fine to your one.
The coils usually fire good when cold. You let them heat up and the spark gets worse as they get warmer.
A coil tester is just a make and break circuit with an adjustable point gap. There is a switch to let current flow through the coil to let it warm up. The testers also allow you to test condensers.
The coil on my 65 failed during a parade one year. It ran fine for the first half of a mile parade. Then it started running rough and then just died. I let it cool and drove home. Put a tested good coil on and it has been fine since.
I have included a picture of some commercial units I own or have owned.
Here is a link a to a cheap way to build your own:
Model A Restorer's Club - Coil Tester
Attachments
Joined
·
12,382 Posts
I do so appreciate the scientific approach to coil testing. If I were in a position to have the opportunity to coil test, then, the coil testing diagram would e super addition to my tool crib. It's an inspiration to the culture of our craft.
But, sometimes us guys at the bottom of the food chain, can only sub out and try a new coil as the quickest alternative.
But, sometimes us guys at the bottom of the food chain, can only sub out and try a new coil as the quickest alternative.
Joined
·
5,791 Posts
thought i'd get a laugh out of it , my older brother did that to me when i was 10 , i didn't bug him as much to help on his mustang after that .
Joined
·
1,086 Posts
im so doing that to my friend the next time he holds down the horn while im trying to fix somthing
Joined
·
1,883 Posts
1 - 20 of 28 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
