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coil testing

4K views 18 replies 7 participants last post by  SickDog 
#1 ·
any one tell me what the ohms should be and how to test the coil to see if its bad :eek:
 
#2 ·
;)
 

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#4 ·
#5 ·
ok tried 3 different coils and no go have 12 volts at both terminals of coil when key is on so i'm thinking its a bad ecm becouse don't they controll the on off trigering of the coil.
 
#6 ·
cookjer24 said:
ok tried 3 different coils and no go have 12 volts at both terminals of coil when key is on so i'm thinking its a bad ecm becouse don't they controll the on off trigering of the coil.
Yes they do, and they are known for going bad.
 
#8 ·
The ECM grounds to the firewall where it bolts up. Poor grounding there can cause it to fail. What I've done in the past is sand the firewall where it bolts down to bare metal to make sure it had a good ground. After that mine has lasted ever since. I went threw a good handful of the at one point
 
#9 ·
phillip637 said:
The ECM grounds to the firewall where it bolts up. Poor grounding there can cause it to fail. What I've done in the past is sand the firewall where it bolts down to bare metal to make sure it had a good ground. After that mine has lasted ever since. I went threw a good handful of the at one point
He's right, it may not be grounded. Didnt think of that :p
 
#12 ·
cookjer24 said:
its grounded made sure of that. pretty sure it is stock from the factory back in 78 so its time for a new one.
Yea I'd go get another one. They should be in stock at your local parts store. And even if that's not the problem it's never a bad idea to have a spare one around.
 
#13 ·
phillip637 said:
Yea I'd go get another one. They should be in stock at your local parts store. And even if that's not the problem it's never a bad idea to have a spare one around.
X2.
 
#15 ·
hoov100 said:
Let me rephrase that :D

Make sure the dizzy is getting 1.5 volts and make sure the ignition module is grounding the coil.
Where is the dizzy getting 1.5 volts from?

The distributor does not "get" any voltage (except the cap and rotor end). The magnetic pickup generates a very low voltage pulse signal to tell the module to fire the coil.
 
#16 ·
cookjer24 said:
ok tried 3 different coils and no go have 12 volts at both terminals of coil when key is on so i'm thinking its a bad ecm becouse don't they controll the on off trigering of the coil.
i think what the OP is saying is that the ECM is failing to provide the grounding cycle for the coil. are these known coils that your are testing with?

however you will get voltage on both posts if the primary winding is ok. there is an ohm spec for the seconadary to primary windings so check that too.

if the coil tests good hook up your test light in series after the coil. like this:

Power wire -> Coil -> Test Light -> ECM.

crank the engine and watch for a flashing test light. if it flashes with no spark induced, the coil is no good and the electronics are ok. if is doesnt flash, the electronics are suspect and need further testing.

either the sensor in the dist. is bad or the ECM is bad. it is possible to test the output signal from the dist. if that tests good, its the ECM.

its a process of elimination because testing the ecm circuits is impractical

hoov100 said:
Let me rephrase that :D

Make sure the dizzy is getting 1.5 volts and make sure the ignition module is grounding the coil.
the ecm controls the ground to the coil via a transistor thus eliminating points and a condensor. the dist. has a sensor that generates a reference timing signal for the ecm to do its magic.
 
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