Author Topic: Coil Issues  (Read 441 times)

sixt9x33rs

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Coil Issues
« on: March 10, 2018, 06:24:06 PM »
I wanted to share a problem that I had and the end result to fix. I had a misfire at 4500 rpm seemed like a lean problem. So I checked the carb, and ended up rebuilding it which was not the problem. Then changed the fuel pump which resulted in me removing the smog pump to get to the fuel pump. Still not the problem. So I changed out the old 293 coil with a Mallory coil that I have had for 24 years. Bingo bad coil. Since I did not have the correct number coil, I ordered a repo coil with the "298" embossed on the part, correct for a 69 Z28. I thought new coil should take care of the problem. Nope, same misfire at 4500 rpm. Put the old Mallory coil ran great. I thought maybe my plug wires had aged so put in good relatively new wires with the new 298 coil...misfire. So this told me the coil was bad for sure. So put the Mallory coil back in the car, and then put the crappy "correct" date coded Packard wires back on. Car runs great now. But previously I had the old 293 coil on the car with the Packard wires and the car ran fine. Just over the time has this problem surfaced. So I am wondering if I still have a problem masked by the better high output coil?
'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles

KevinW

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Re: Coil Issues
« Reply #1 on: March 10, 2018, 08:56:48 PM »
I had a similar issue, random misfires. Changed a lot, but they went away when I put in a Pertronix flamethrower coil (the black one and I removed the label).  works much better now.  The new coil is a tad bigger in diameter, so I had to get a longer clamp bolt

L78 steve

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Re: Coil Issues
« Reply #2 on: March 11, 2018, 09:02:47 PM »
Its probably the coil. If you test a stock dist. with points on a Sun machine the points will start to bounce at around 4500rpm.
This causes a weak waste spark ATDC and a weak coil cannot recover from this.
With a strong coil this waste spark has no effect on performance.
This can be clearly seen on the Sun Dist. scope.
69 Z/28 Dover White. SOLD
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C. SOLD
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B