Car is bone stock. Started fine last week, now turns over well but no attempt to fire. Checked all obvious parts of the FI system and found no problem. Now looking at electrical. Using inline spark checker the spark seems very weak. Battery shows 12.63 volts but the high side of the ballast resistor is only 11.88 (low side is 5.67). Any thoughts would be appreciated. Thanks
sampanjohn
Condenser or weak battery (enough volts but not enough amps) on those things 9x's out of 10.
Next in line is coil. (unlikely)
Charge battery and try.
Change condensor.
Next in line is coil. (unlikely)
Charge battery and try.
Change condensor.
5.6 volts is not going to produce much of a spark. The hot side of the balast resistor should be the same as the positive side of the battery. If it isnt you need to fix that first, the low side of the balast should be around 9-10 volts. I would guess you have a bad connection somewhere either on the hot side or the ground. Vettes are known for grounding and electrical problems. You can prove if the resistor is the issue by running a wire from the a hot lead directly to the + side of the coil and try to start it. It wont hurt it to run this way to test. You could also have a bad ignition switch that is dropping voltage.
If the above test works and it starts, start checking the battery voltage through the harness to see where it is falling off and you will have found your bad connection. My bet is at the positive post of the starter or the ignition switch is no good.
Dont forget to check the grounds also between the battery and the engine block.
Chet
If the above test works and it starts, start checking the battery voltage through the harness to see where it is falling off and you will have found your bad connection. My bet is at the positive post of the starter or the ignition switch is no good.
Dont forget to check the grounds also between the battery and the engine block.
Chet
Doc here, 
imp:
BE SURE your secondary Ignition wire is hooked up and correct.
It runs from the "I" or "R" side of the starter solenoid, to the Coil side (past the ballast) of the coil.
This wire will only have 12 volts in CRANK mode and 0 volts in Run, If it is missing the car will either be a "Hard Start" or not start at all..
IF that is good...
Open the points up, and with a DVOM set to Vx50 or autorange, measure the COILSide of the ballast resistor.
It SHOULD read the same as the Battery side or ignition wire side of the ballast. Or, if it's 12.63 Volts, at the ignition wire side it should be the same on the Coil side. If not the ballast is bad.
NEXT, CLOSE the points (turn the key off first .. or you'll be cussing me out..) then turn it on, and measure again, It should read 12.63 Volts (or thereabout) on the Ignition side of the ballast, and between 6 to 9 volts on the coil side. If it is lower, test the coil primary.
Disconnect the coil, measure the primary side of the coil. DVOM set to R X 1 , Calibrated to 000, It should read LESS than an ohm, BUT more than 000, If higher or 000, toss the coil, it's bad.
You SHOULD also check the Secondary side, with the DVOM set to Ohms, R X 10K or higher, It should read Between 10,000 and 11,000 ohms, out of that range toss it, it's bad.
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If all checks good, Take a Jumper cable and clamp it to the battery ground , and clamp the other end to the engine block and see if that doesn't correct the problem, If it does Install a PROPERLY Bonded central Ground buss system at or near the starter on the block from the battery.
Docimp:
imp: BE SURE your secondary Ignition wire is hooked up and correct.
It runs from the "I" or "R" side of the starter solenoid, to the Coil side (past the ballast) of the coil.
This wire will only have 12 volts in CRANK mode and 0 volts in Run, If it is missing the car will either be a "Hard Start" or not start at all..
IF that is good...
Open the points up, and with a DVOM set to Vx50 or autorange, measure the COILSide of the ballast resistor.
It SHOULD read the same as the Battery side or ignition wire side of the ballast. Or, if it's 12.63 Volts, at the ignition wire side it should be the same on the Coil side. If not the ballast is bad.
NEXT, CLOSE the points (turn the key off first .. or you'll be cussing me out..) then turn it on, and measure again, It should read 12.63 Volts (or thereabout) on the Ignition side of the ballast, and between 6 to 9 volts on the coil side. If it is lower, test the coil primary.
Disconnect the coil, measure the primary side of the coil. DVOM set to R X 1 , Calibrated to 000, It should read LESS than an ohm, BUT more than 000, If higher or 000, toss the coil, it's bad.
You SHOULD also check the Secondary side, with the DVOM set to Ohms, R X 10K or higher, It should read Between 10,000 and 11,000 ohms, out of that range toss it, it's bad.
If all checks good, Take a Jumper cable and clamp it to the battery ground , and clamp the other end to the engine block and see if that doesn't correct the problem, If it does Install a PROPERLY Bonded central Ground buss system at or near the starter on the block from the battery.
Doc
imp:-
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