My '93 won't crank. It acts like it wants to just a little at first, but I don't see any arc at the plugs when I spin it over. NO CODES. Possably due to the fact that I keep having to disconnect the battery to keep it from draining it down. (I know, I don't have just one problem, it always come in multiple multiples! Such is my lot in life). I assume disconnecting the power clears the alarms. I can't get it started, so it sees no problems to report.
I replaced the opti about a year age, about a 1000 miles on the new opti. It ran great up until now. I didn't replace the coil, or the ignition module. I thought about buying a new coil to try, it's only $15 at autozone, then the ignition module later (at $75, that will have to wait). Should these components have been changed out when the distributor was changed? What is your guess as to what the problem is?
Thanks for your help.

 

Check the wiring harness that goes under pass side fuel rail cover to the opti, check the coil wire. After that the ignition module wiring and take the module to an autoparts store and have it tested. With no codes that would seem a logical path for checking the no spark situation.

 

Yes, I agree. Check the wiring connections.

 

If I can ask a dumb follow up question, Where is the ignition module? How can I identify it?
Thanks for your help...

 

oh, dear... you need a book... the Helm Factory Service Manual is your friend... www.helminc.com. GET IT!!!!

As for the ignition module... it's on the right head, under the coil, at the front, behind the PS resevour.

Check the coil wire, too. They have a tendency to chaffe.

Check the harness to the coil and ICM. They are prone to wearing out. If you can clean the contacts, and manipulate them to fire, I would get a new harness pigtail (I know ecklers sells them).

 

Here are a few tests to get you started on the problem since you don’t have your book as of yet as recommended.

Remove high voltage coil wire from coil. Attach another wire from coil and hold near ground while some one cranks engine. If is arks, coil wire could be bad. If it does not, then continue trouble shooting.

Be the utmost of careful not to short anything to ground. ING key off, remove (ICM) ignition module connector and check the ground connection on pin C - BLK/WHT wire, (resistance about 0) .

Next, “Key on”, check for 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 ECM could be source of problem. Figuring out which one might take further troubleshooting.

If AC volts are good, the IGN coil should put out spark. If it does not, there is a small chance the coil is bad. The ICM might be a higher probability.

Don’t know why you disconnect your battery but it would be a good idea to get the codes if any are present, it might help.

 

The first suprise was how weak the spark at the coil was. Very small. The wires are fairly new, 8mm Taylors, about 30K miles ago. Ground was present on pin C. Key on position put 12V to pin A and D. Fuse 25 OK. (I pulled out every fuse in the panel, checked each one just a few days ago, but I checked again) Good check. With the meter on term.B and the moter turning over I saw a fast flutuation from V-mv. I saw it go up in the volts range, but hard to see how far. Maybe I need to find my old Simpson 260 Analog meter. My problem is that I'm between moving. I did find my manual, sorry for that.
I still don't know where to go next. I'm still thinking coil, try, then ICM. I called autozone and advanced, there's some confusion about weather they can test the ICM. I'm looking at the process. Maybe I should remove the Pwr strg pump, and hoses? Does the coil have to be removed before the ICM?
The problem with these cars is that the go together in layers. You gotta remove one thing to get to the next. On and on.
I really appreciate your help pcolt94. It gave me a better understanding.
The battery has to be disconnected because it drains down the system when left connected. It's another problem for me to solve. Right now, there's nothing sadder the a vette that won't run, and I'd like to at least get it to run. Thanks again....

 

I have heard from other posts that Autozone can check the ICM. It is basically an amplifier which takes the 4 to5 volt square wave pulse from the ECM (pin B) and amplifies it to about 40 volts peak to peak (as read on a o-scope) and drives the coil. If the ICM is bad and does not drive fully, the spark can be weak from the coil. Also, if the pulse from the PCM is not enough, it can cause your problem, lets hope not.

Coils are cheep but a pain to change. The ICM is expensive and easy to replace. Since you have a solid problem, I would at least try to get the ICM checked. They are separate installations.

By the way, you can get a coil, don’t mount it, but you can electrically hook it up (all plugs) and just let it hang, (have done it). If that is not the problem, just return it clean, no marks.