Strange TPI Ignition Coil Problem
Thread Starter
Burning Brakes
Joined: Nov 2005
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From: Leander Texas
Strange TPI Ignition Coil Problem
I took the Corvette out for a drive today. I was about a mile from the house when the engine began to have an intermittent misfire, and the tach started to jump. I turned around an went back to the house.
My first thought was a lose coil feed wire, but when I popped the hood I heard a strange rhythmic electrical chirping noise coming from the remote coil/distributor area.
I found a crack in the distributor cap near the coil tower when I stuck my finger on the top of the cap to see if it felt like it was being hit by the rotor (the visible spark jumped 1/2 inch).
I changed the cap and rotor, and still had the jumping tach, and the electrical chirp. I started listening with a piece of rubber hose, and could hear the chirp coming from the coil in the tach lead connection area in time with the jumping tach.
I'll change the coil in the morning, but this experiance is a first for me. I have never heard a coil make any noise in all my 15+ years of turning wrenches.
DR.Jay the baffled.
My first thought was a lose coil feed wire, but when I popped the hood I heard a strange rhythmic electrical chirping noise coming from the remote coil/distributor area.
I found a crack in the distributor cap near the coil tower when I stuck my finger on the top of the cap to see if it felt like it was being hit by the rotor (the visible spark jumped 1/2 inch).
I changed the cap and rotor, and still had the jumping tach, and the electrical chirp. I started listening with a piece of rubber hose, and could hear the chirp coming from the coil in the tach lead connection area in time with the jumping tach.
I'll change the coil in the morning, but this experiance is a first for me. I have never heard a coil make any noise in all my 15+ years of turning wrenches.
DR.Jay the baffled.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
YES, if you take a HEI outta the car, and hook it up to 12 volts, clipped across a battery....and spin the shaft, looking out for the cap leads, you will hear a distinct clunk from the coil for every pulse......
second off, check your grounding on that, sometimes forgetting the ground strap/clip/wire off the coil frame to that center terminal on the 3 wire plug and the coil then arcs to the bat or tach terminal with HV....see the burn marks.....
another thing to watch for is the crimped leads on the HV coil...the red and yellow/white lead...they are not soldered from the factory, but crimped right through the formvar of the copper wire, can be a lousey connection...caught one some years ago, pants down/proved it...and soldered it for several years use outta that coil....
I solder all them now....
second off, check your grounding on that, sometimes forgetting the ground strap/clip/wire off the coil frame to that center terminal on the 3 wire plug and the coil then arcs to the bat or tach terminal with HV....see the burn marks.....
another thing to watch for is the crimped leads on the HV coil...the red and yellow/white lead...they are not soldered from the factory, but crimped right through the formvar of the copper wire, can be a lousey connection...caught one some years ago, pants down/proved it...and soldered it for several years use outta that coil....
I solder all them now....
Thread Starter
Burning Brakes
Joined: Nov 2005
Posts: 1,143
Likes: 0
From: Leander Texas
YES, if you take a HEI outta the car, and hook it up to 12 volts, clipped across a battery....and spin the shaft, looking out for the cap leads, you will hear a distinct clunk from the coil for every pulse......
second off, check your grounding on that, sometimes forgetting the ground strap/clip/wire off the coil frame to that center terminal on the 3 wire plug and the coil then arcs to the bat or tach terminal with HV....see the burn marks.....
another thing to watch for is the crimped leads on the HV coil...the red and yellow/white lead...they are not soldered from the factory, but crimped right through the formvar of the copper wire, can be a lousey connection...caught one some years ago, pants down/proved it...and soldered it for several years use outta that coil....
I solder all them now....
second off, check your grounding on that, sometimes forgetting the ground strap/clip/wire off the coil frame to that center terminal on the 3 wire plug and the coil then arcs to the bat or tach terminal with HV....see the burn marks.....
another thing to watch for is the crimped leads on the HV coil...the red and yellow/white lead...they are not soldered from the factory, but crimped right through the formvar of the copper wire, can be a lousey connection...caught one some years ago, pants down/proved it...and soldered it for several years use outta that coil....
I solder all them now....
This was a first for me. The noise coming from the remote coil was loud enough that it could be heard over the side pipes when the hood was up. It was a sound like the crack of a high voltage arc.inside the coil itself.
I just found it strange that this noise is the sign that the coil was begining to fail. Usually they just leak oil, or don't produce a spark.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
OH, you got a small cap HEI, I missed that, my comments are not valid then....sorry....yeh, an arcing inside that external type coil is terminal failure....but how do you know it's clunking or an actual sound of an electronic arc?? if you sure ti's a high freq sound of a arc...well, time for a new coil....IMO....damn surely try one anyway....
Thread Starter
Burning Brakes
Joined: Nov 2005
Posts: 1,143
Likes: 0
From: Leander Texas
OH, you got a small cap HEI, I missed that, my comments are not valid then....sorry....yeh, an arcing inside that external type coil is terminal failure....but how do you know it's clunking or an actual sound of an electronic arc?? if you sure ti's a high freq sound of a arc...well, time for a new coil....IMO....damn surely try one anyway....
Thread Starter
Burning Brakes
Joined: Nov 2005
Posts: 1,143
Likes: 0
From: Leander Texas
update: Problem Solved
I was able to get the coil swapped out this afternoon. The tach works correctly now. The noise is gone also, and I only spent $15.oo instead of $40.oo since they were out of the more expensive coil. The car is running better also. The intermittent trouble code #43 ( ESC fault ) that I would get when I was hard on the accelerator didn't rear its head during the test drive. So the problem is solved, and I'm Happy with the car again. 
