topspin

On a 96 LT-1; if the crank sensor is bad will this engine allow the ign coil to spark? What is the cause normally for the digital tach to not function? Could my crank/cam sensor in the opti be causing these two mal-functions? What about a wire shorting which would cause these? Engine cranks over and has about 42 lbs of fuel pressure. I feel like something is grounding or shorting out the spark. Can I unplug the ign coil connector and ohm the two wires? My connector has 3 pins but only two wires going into it. With the key in the on position can I put my meter on the two wires ( with it unplugged from the coil ) and check for 12 volts? If so do I check just between these two wires or can I put the red probe of meter on the pink wire and the black lead to engine ground? The manual I was looking in ( Haynes ) says I can check these two wires for 12 volts but I don't beleive both wires shold have 12 volts on them in the on position. I also metered these two wires for ohms with ign switch off and both were reading no resistance when checked to the engine. It appears both are grounded in the off position but I thought only the green wire should read groung. I beleive these two wires are the input voltage to the primary side of the coil so how can 12 volts not be shorting out if both wires read grounded in the off position. So could my pink wire be shorting to the engine and causing the no fire from my coil and also related to the tach not working the last time engine ran. If my battery voltage only shows 11.1 volts at the crk fuse while engine is cranking could it not fire? I feel maybe something is causing to much of a voltage drop because it goes from 12.3 to 11.1. Another theory is maybe my battery does not have quite enough voltage to properly fire the system. Should the battery be 13 volts or more in the on position and while cranking it would loose 1 volt thus giving it 12 volts to fire???

Casethecorvetteman

12 volts is enough to fire, the thing that makes it drop is the starter motor.

Check all the related wiring, make sure its not chaffed through somewhere,
Check all the connections at the ECM,
Check all the connections to the distributor,
Check the ICM and its connection,
Check for any DTCs

pcolt94

There are many places to start, hear is one to check part of the ignition circuit.

Here are a few tests to get you started on the problem. Be the utmost of careful not to short anything to ground. ING key off, remove Ignition Control Module connector and check the ground connection on pin C - BLK/WHT wire, (resistance about 0) .

Next, “Key on”, check for about 12 volts at pin A - PNK /BLK wire and pin D – Dark green wire. If no voltage check the coil fuse 10A, (#25?), or wiring.

If all is good, set meter to read AC volts and connect probe to terminal B – white wire. Have some one crank engine, meter reading should be between 1 to 4 volts. Key off! Put connector back on. If OK, this indicates opti and PCM are probably working. If not, opti or PCM could be source of problem. Figuring out which one might take a shop to do this. Both are expensive parts and you just can’t guess at it. If all is good, the Ignition Control Module could be defective. Although the coil could cause the same symptom, the ICM is more of a likely candidate.

To eliminate the coil wire, attach another wire from coil and hold near ground while some one cranks engine. If is arks, coil wire could be bad usually near the water pump.