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Premium Member
1,652 Posts
Discussion Starter · #1 ·
Ran the car Wed and it just felt weak. Pulled the plugs and found 2 wet ones, 3 and 6, on the same coil. I suspect I have a weak coil. How do I check it and what numbers am I looking for? If it is bad, is it normal to just change 1?



Scottie's GNZ

71 240Z/GN Power/Corvette IRS

Premium Member
43,735 Posts
well, you can try the resistance test and see if it reads 11-13 ohms between the front and rear terminals of the coil.

If it is far off of that, then the coil is bad but you have to replace the coil pack completely, not just one.

if the resistance is in the range, then it could be the module, or it could be the coil as they don't always flunk the test.....I would try it hot.

Resident Idiot
11,462 Posts
KDK has the Caspers coil pack tester. Or you can just try this coil I have here. It's for the mazda and not being used yet.


Stock Block, Stock Cam, PTE-52, Champion Heads, V4, MSD50's, TH DP, JayJackson 62mm TB, 16position MaxEffort Chip. 3680# with Driver
12.0 @ 116.5mph w/20psi using 17.9* timing

mailto:[email protected][email protected]</A>

46 Posts
ignition coils must be able to pass three tests: #1 secondary resistance cold #2 available voltage test using ST125 (spark tester ) #3 secondary resistance hot (operating temperature)
secondary resistance @ 75 degrees F
TYPE 1:10,000-13,000 OHMS ,called MAGNOVOX
coil which is used on TR's
TYPE 2:5,000-7,000 OHMS
it is imporant to check secondary resistance
when the engine is cold,and then again when
the engine is hot. remember that a coil's
resistance will increase somewhat with tem-
perature.at operating temperature,look for
no more than 2,000 ohms variation between
coils rather than strictly using the above
in some cases,it is best to leave the ST125
attached to the coil being tested for up to 10 minutes to make sure the coil's internal
insulation does not break down.
if a coil fails the ST125 test,make sure the
plug wires do not have excess resistance.
TYPE 1: .35-1.5 ohms
TYPE 2: .35-1.5 ohms
this is measured under bottom of coil at
secondary is measured across coil towers.
this information taken from BUICK driveability quick reference sheet.
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