truck wont start, how do i test coil? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

datguysaL · 06-02-2010, 07:42 PM

my 85 chevy wont start, i checked and its gettin power to the distibutor, but its not putting anything out, no spark no where.

i took the coil and module to get tested at the parts store,

the module tested good.

they didnt know how to test the coil.
how can i test this?? i have a dmm, ohmeter.

Pyrotechnic · 06-02-2010, 08:00 PM

Check the resistance between the yellow and red wires, then check the resistance between the red wire the the brass button in the center of the coil where the spark comes out.

The yellow and red wires is the primary resistance, it should be somewhere around 1 Ohm but could possibly be as low as tenths of a ohm. The red wire and center button is the secondary resistace, which will be somewhere in the thousands of ohm's range.

If either one is infinite or zero resistance, the coil is bad.

datguysaL · 06-02-2010, 08:08 PM

thanx Pyrotechnic

check and got this

red and yellow wires got .4 ohms
red and button got infinate or "OL"

time for a new coil.. thanx alot...

Pyrotechnic · 06-02-2010, 08:16 PM

Actually try that again for me I think I may have given you bad info. Try the yellow wire and button and see what you get.

datguysaL · 06-02-2010, 08:23 PM

checkd again.

red to button- "OL" or infinate
yellow to button- "OL" or infinate

red to yellow- .04 ohms

Pyrotechnic · 06-02-2010, 08:27 PM

It looks like it's bad then. I can't ever remember which wire you test with the center button, but one of them should have given you a resistance.

datguysaL · 06-02-2010, 08:40 PM

thanx,

James McClure · 06-03-2010, 07:48 AM

Sal, Pyro has it right kind of. There are 2 coils inside the coil itself. One is primary (12 V) the other is secondary that goes to the plugs. Each has to be a complete circut to function properly. Yellow and red wires are primary. The center hub on the coil and the black wire are the secondary. Basicly the black wire is the ground side of the sparkplug. I have seen this before. If you changed the cap or the coil you might have missed the steel tab that sits under one of the coil retaining screws between the cap and coil and goes to the wire connection lug on the side of the cap and from there is grounded. Let us know what you find. Jim

Slonaker · 06-03-2010, 11:35 AM

When my module went out, I had it tested. The first store tested it multiple times, and it tested good as many times as it tested bad. Then they tested one off the shelf, and the same thing happened. The second store didn't do much better. Apparently testing modules is beyond the abilities of the parts store counter people. Keep that in mind if the coil doesn't fix the problem...

Slonaker

datguysaL · 06-03-2010, 06:54 PM

thanx errbody

i went today and got me a new coil, put it in and started up on the first crank.

i didnt get a chance to test the black wire to the tab, awready had bought the new one and trashd the old one at the autoparts trash can.

73chevyman · 06-03-2010, 09:29 PM

hahahaha sounds like me datguy get the new part and while heading back to your truck throw the old 1 in the trash lol glad you fix your problem...........

06-02-2010, 07:42 PM	#1
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	truck wont start, how do i test coil? my 85 chevy wont start, i checked and its gettin power to the distibutor, but its not putting anything out, no spark no where. i took the coil and module to get tested at the parts store, the module tested good. they didnt know how to test the coil. how can i test this?? i have a dmm, ohmeter. Attached Images

06-02-2010, 08:00 PM	#2
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: truck wont start, how do i test coil? Check the resistance between the yellow and red wires, then check the resistance between the red wire the the brass button in the center of the coil where the spark comes out. The yellow and red wires is the primary resistance, it should be somewhere around 1 Ohm but could possibly be as low as tenths of a ohm. The red wire and center button is the secondary resistace, which will be somewhere in the thousands of ohm's range. If either one is infinite or zero resistance, the coil is bad. __________________ 1977 GMC Sierra Grande Last edited by Pyrotechnic; 06-02-2010 at 08:01 PM.

06-02-2010, 08:08 PM	#3
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: truck wont start, how do i test coil? thanx Pyrotechnic check and got this red and yellow wires got .4 ohms red and button got infinate or "OL" time for a new coil.. thanx alot...

06-02-2010, 08:16 PM	#4
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: truck wont start, how do i test coil? Actually try that again for me I think I may have given you bad info. Try the yellow wire and button and see what you get. __________________ 1977 GMC Sierra Grande

06-02-2010, 08:23 PM	#5
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: truck wont start, how do i test coil? checkd again. red to button- "OL" or infinate yellow to button- "OL" or infinate red to yellow- .04 ohms

06-02-2010, 08:27 PM	#6
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: truck wont start, how do i test coil? It looks like it's bad then. I can't ever remember which wire you test with the center button, but one of them should have given you a resistance. __________________ 1977 GMC Sierra Grande

06-02-2010, 08:40 PM	#7
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: truck wont start, how do i test coil? thanx,

06-03-2010, 07:48 AM	#8
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: truck wont start, how do i test coil? Sal, Pyro has it right kind of. There are 2 coils inside the coil itself. One is primary (12 V) the other is secondary that goes to the plugs. Each has to be a complete circut to function properly. Yellow and red wires are primary. The center hub on the coil and the black wire are the secondary. Basicly the black wire is the ground side of the sparkplug. I have seen this before. If you changed the cap or the coil you might have missed the steel tab that sits under one of the coil retaining screws between the cap and coil and goes to the wire connection lug on the side of the cap and from there is grounded. Let us know what you find. Jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

06-03-2010, 11:35 AM	#9
Slonaker Insert Witty Text Here Join Date: Oct 2002 Location: San Antonio, TX Posts: 3,415	Re: truck wont start, how do i test coil? When my module went out, I had it tested. The first store tested it multiple times, and it tested good as many times as it tested bad. Then they tested one off the shelf, and the same thing happened. The second store didn't do much better. Apparently testing modules is beyond the abilities of the parts store counter people. Keep that in mind if the coil doesn't fix the problem... Slonaker __________________ '86 Chevy C10 (Sold 04/19/13 ) Stock '01 Silverado

06-03-2010, 06:54 PM	#10
datguysaL Registered User Join Date: May 2009 Location: Houston, TX Posts: 155	Re: truck wont start, how do i test coil? thanx errbody i went today and got me a new coil, put it in and started up on the first crank. i didnt get a chance to test the black wire to the tab, awready had bought the new one and trashd the old one at the autoparts trash can.

06-03-2010, 09:29 PM	#11
73chevyman Registered User Join Date: Nov 2008 Location: Lusby, MD Posts: 563	Re: truck wont start, how do i test coil? hahahaha sounds like me datguy get the new part and while heading back to your truck throw the old 1 in the trash lol glad you fix your problem........... __________________ http://67-72chevytrucks.com/vboard/group.php?groupid=37 73 C10 Fleetside If it ain't a Chevy it's foreign http://hotridesmag.com/



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