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Ohming A Coil Question
Thread Starter
Racer
Joined: Sep 2005
Posts: 385
Likes: 8
From: north branford ct
Ohming A Coil Question
I was going to ohm the coil and both my FSM and chiltons show a picture of how to ohm the coil, that would be good if you could see the picture. I can make out the pick up pics and the ohms where ok, but the other one sucks even with a magnafing glass. It shows the cap and coil upside down. does anyone have a closeup of which terminals you do the two tests on---Thanks guys for any help
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
If you're trying to check the coil, you just use the two probes one to the battery side, the other to the tach side, there are only two wires-it should read zero or nearly zero. If you're talking pickup there is only 2 terminals there also, that should read at a steady value between 500 and 1500, but you have to wiggle those wires while testing.
BTW, I see you're going through most of the tests I've already been through. Post your injector ohms here. I know there's some bad ones (most of em) but you might get more feed back on this post-the other is waaaaaay to long.
BTW, I see you're going through most of the tests I've already been through. Post your injector ohms here. I know there's some bad ones (most of em) but you might get more feed back on this post-the other is waaaaaay to long.
Last edited by rick lambert; May 9, 2006 at 07:22 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Measuring the dc resistance of a coil or windings of a transformer will only show gross coil failures. A much better test would be to measure the inductance and the "Q" of the winding and compare it to the measurement of a known good coil. A Maxwell connected wheatstone inductance bridge which measures low "Q" coils is best.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
well, jfb knows a hellava lot more than me about the electrical side of our vettes, and yes, the test only tells you if the coil is bad, the one I helped you with. But, if you're going all the way through your ignition system..then take the ignition module to someone like autozone and have it checked too.
So far, you've found at least 1 bad plug wire, and if you do post the injector ohms you found here..well, I'm sure most will concur...you have some bad injectors also. Why these animals can run strong as hell when there's a definite problem with 1 or more cylinders,only goes to show why these are such strong engines.
So far, you've found at least 1 bad plug wire, and if you do post the injector ohms you found here..well, I'm sure most will concur...you have some bad injectors also. Why these animals can run strong as hell when there's a definite problem with 1 or more cylinders,only goes to show why these are such strong engines.
Thread Starter
Racer
Joined: Sep 2005
Posts: 385
Likes: 8
From: north branford ct
injector ohms
Quote:
Originally Posted by rick lambert
Hey, when you ohm your injectors do it hot and cold..belive they should ohm around 14, and they all should be within .5 ohms,if memory serves, just check to make sure.
Good Idea rick to post this again as the other is so long -Thanks again
After reading your post again I see you ohm injectors hot and cold--didnt see the hot part yesterday but I ohmed them cold and they look screwed up to me, but why does the car run so good under full power. Here they are.
#1-16.5
#2-4.7
#3-16.4
#4-16.4
#5-5
#6-12.3
#7-8.1
#8-7.2
I will try them hot and see if there is a difference---Boy would it be nice to just have to worry about cleaning and waxing this car some day--its black but I refuse to clean it till Im done working on it.
Originally Posted by rick lambert
Hey, when you ohm your injectors do it hot and cold..belive they should ohm around 14, and they all should be within .5 ohms,if memory serves, just check to make sure.
Good Idea rick to post this again as the other is so long -Thanks again
After reading your post again I see you ohm injectors hot and cold--didnt see the hot part yesterday but I ohmed them cold and they look screwed up to me, but why does the car run so good under full power. Here they are.
#1-16.5
#2-4.7
#3-16.4
#4-16.4
#5-5
#6-12.3
#7-8.1
#8-7.2
I will try them hot and see if there is a difference---Boy would it be nice to just have to worry about cleaning and waxing this car some day--its black but I refuse to clean it till Im done working on it.
Thread Starter
Racer
Joined: Sep 2005
Posts: 385
Likes: 8
From: north branford ct
Originally Posted by rick lambert
If you're trying to check the coil, you just use the two probes one to the battery side, the other to the tach side, there are only two wires-it should read zero or nearly zero. If you're talking pickup there is only 2 terminals there also, that should read at a steady value between 500 and 1500, but you have to wiggle those wires while testing.
BTW, I see you're going through most of the tests I've already been through. Post your injector ohms here. I know there's some bad ones (most of em) but you might get more feed back on this post-the other is waaaaaay to long.
BTW, I see you're going through most of the tests I've already been through. Post your injector ohms here. I know there's some bad ones (most of em) but you might get more feed back on this post-the other is waaaaaay to long.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
I'll see if I can explain, once again this is a good ..bad test....no in betweens.
with the cap and coil still assembled put your ohm probe...black to the center buttom of the cap, inside the dist., put the red probe to the tach spade (that's the place your tach plugs into the dist.) if you see OL on the meter that means it's shot, if you hold both probes in the air it should read the same, that's called infinite. The other test you asked about, you put the probe to the same button (electrode) in the cap, the other goes to the center spade (there's three), once again, if you get OL, it's shot. HOPE I explained that clear enough.
One thing I should say is, if the coil was shot-you wouldn't be going anywhere.
with the cap and coil still assembled put your ohm probe...black to the center buttom of the cap, inside the dist., put the red probe to the tach spade (that's the place your tach plugs into the dist.) if you see OL on the meter that means it's shot, if you hold both probes in the air it should read the same, that's called infinite. The other test you asked about, you put the probe to the same button (electrode) in the cap, the other goes to the center spade (there's three), once again, if you get OL, it's shot. HOPE I explained that clear enough.
One thing I should say is, if the coil was shot-you wouldn't be going anywhere.
Last edited by rick lambert; May 10, 2006 at 09:07 AM.
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Thread Starter
Racer
Joined: Sep 2005
Posts: 385
Likes: 8
From: north branford ct
Thanks rick, It was the middle one that I couldnt see. I just bought a new gm cap and figured to check it while doing the swap. I know what you mean about the coil being bad and the car not going anywhere, but Im running out of things to check. I noticed the aftermarket cap I bought last week,all the posts where loose and wiggleing--thats the only reason the cap and coil are off. By the look of things so far it looks like the injectors(OH MORE FUN)
Thanks
Thanks
Thread Starter
Racer
Joined: Sep 2005
Posts: 385
Likes: 8
From: north branford ct
Put the new coil in( ohmed it first, got some readings on this one ) It starts right up when hot again just like it did before the coil went south. Injectors are next
Last edited by mudslide; May 12, 2006 at 08:21 AM. Reason: miss spell