weak spark

Tom H · Post by **Tom H** » Wed Jul 10, 2002 8:45 am

Help!

We recently replaced the engine in a 72 Super with a rebuilt longblock 1600. (The old engine ran but was fairly weak.)

In the R&R, we installed with new parts the generator, voltage regulator, points, plugs, condenser, cap, rotor and coil. The distributor is mechanical rather than vacuum. All of the tin was removed and painted, and new rubber seals and firewall insulation installed.

Here's the problem: The spark coming from the coil, when tested by putting the coil wire next to a ground (the distrib hold-down clamp), is blue to white but very, very weak -- the wire end needs to almost touch the bolt.

We're stumped. One theory suggests that the paint on the new longblock where it mates to the transaxle is preventing a good ground. We did not mess with the grounding strap on the transaxle.

Any ideas? Your help is greatly appreciated.

Thanks!

Bucko · Post by **Bucko** » Wed Jul 10, 2002 9:23 am

The coil needs a good ground also. To test your theory, attach a wire that can connect the coil hold down clamp to a good ground such as the trans (bypass the painted part). Then check your spark again. It should jump at least a 1/4 gap.

I suspect that the coil is not getting a good ground.

Post by **Marc** » Wed Jul 10, 2002 9:52 am

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Bucko:
<B>

I suspect that the coil is not getting a good ground.</B><HR></BLOCKQUOTE>

Nonsense, it's an autotransformer and will work whether grounded or not.
It'd be simple to test your block-not-grounded theory by connecting a jumper cable, but if the engine's bolted to the trans it'd more than likely get a good ground through the mounting bolts if nothing else, (like the throttle cable).
I think you'll find it something much more mundane like points that need cleaning or a defective condenser or coil.
Try this - disconnect the Term 1 wire from the coil, leaving only the power from the ignition switch hooked up to Term 15. Using a jumper wire between Term 1 and ground, see if you don't get a decent spark each time you disconnect it. (If not try another coil).
Next hook the Term 1 wire back up and see if you can get a good spark each time you open the points; also try rotating the engine so that the points are open and then bridge across them with your screwdriver tip. If the screwdriver makes better points than the points do, they need attention. If you get a good spark under these tests but not when the engine's cranking, and the voltage to the coil isn't being dragged down excessively while cranking, then the condenser is suspect.

captCRUNCH · Post by **captCRUNCH** » Wed Jul 10, 2002 3:40 pm

might sound silly...but what about the plug wires themselves??? you sure that they don't have a crack in them??? double check the points. if you have anouther dist & coil kicken around, you could always switch them and see if the spark improves. if it does you know what your problame is.

rich2481 · Post by **rich2481** » Thu Jul 11, 2002 6:29 am

i always check out spark by holding the wire in one hand and putting the other hand on the bumper, Oh wait I get a friend to do that

RICHARD A HUNT · Post by **RICHARD A HUNT** » Fri Jul 12, 2002 9:17 pm

You may consider checking that you have 12v to the coil first. If you think a bosch blue is narly, try a 911 coil or a Dyna ign coil, BZZZZZZ. I have, DAMN!!!!! That HURTS!!!

Rick (M.C. Drag Racer).