The PCM seldom fails. But pulling codes would sort that out. Not starting, no spark, and no indication of activity on the tach are common indicators of an Opti optical module failure, or corroded Opti harness connector terminals, or damaged wires in the short Opti harness connector from the bracket on the passenger side of the intake manifold to the Opti.

http://shbox.com/1/evap_sol.jpg

Loss of the low resolution signal from the Opti can cause a code for that loss. Problem is the code sets based on the PCM counting high resolution pulses, and if neither high nor low res signal is present, the code can’t set. Additionally, the code does not turn on the SES light. When the code sets it shuts down the fuel system. And, issues with the signals from the Opti can cause the CKP sensor code to set, because the PCM is comparing the signals from the Opti to the signals from the CKP sensor to determine if there is a misfire, but the two signals are too far out of phase.

When your buddy shows up with the volt meter, go right to the white wire on pin B of the ICM connector. This is the wire that carries the pulse that tells the ICM to fire the coil. You want to see a reading in the range of 1 to 4 volts AC. If that signal isn’t there, the ICM can’t fire the coil/no spark. Finish checking the 4 wires in the ICM module.

Then go to checking the 4 wires on the Opti harness. The red wire on pin A is the key, because that is the wire that carries the low resolution pulse to the PCM. This tells us if it’s the Opti or the PCM (unlikely).

 

It is not your PCM but the optispark that will be the problem. The PCM is not getting necessary sensor information to run the engine so from what you have found, it is now pointing to your distributor being the problem.

As you have mentioned, wait for your friend to help you diagnose the optispark and verify that the sensor is bad. The test that Injuneer mentions is one I was never aware of but given how often I have had to replace optisparks I would just spend the money to replace it.

I hope you get your Trans Am running again, soon.

 

My buddy can't come. So I'm going to start taking the Opti out.

I've heard that is easier from underneath with the car up on stand? This way you don't have to take the fans or radiator Out.
I figure this way I can replace all coolant and the water pump while I'm at it.

 

I will be glad to help you and give advice. Taking the Optispark out is not too bad but remembering how everything goes to put it back in may be an issue! I also need to warn you that will have to remove the power steering pulley to access the water pump bolt directly behind it on the right-most side of the pulley. I tried to remove the bolt without removing the pulley and ended up damaging the pulley but thank God I didn't ruin the pump shaft for the pulley. You will need a power steering pulley remover/installer kit which they sell at Harbor Freight for a cheap enough price. If you watch some youtube videos they show you how to work this kit since you won't get any good instructions on how to use it to remove and reinstall the pulley.

You will also need to remove the mounting bracket for the smog pump since one of water pump bolts is directly behind this as well. It is not that much of pain as is the power steering pulley but be sure not to lose the smog pump screws and be careful of how the bracket bolts come out because they are different sizes!

You are also going to want to check the timing cover seal for the water pump shaft. Over time they deteriorate and WILL leak oil which will cover and seep into your new Optispark. These are cheap enough to replace and if you feel yours may be showing signs that the seal has worn down and has a coating of oil I strongly recommend changing it. It is easier than you think and one youtube video made it harder than it should be to remove! I can help you with the process if you need it.

For changing your coolant, don't forget to flush the heater coil. Over time coolant will gunk up in it and since you probably never use the heater in your car but are changing the coolant I recommend cleaning out the connections to the heater coil as well to do a thorough job!

Keep us posted on your progress and don't feel shy to ask for help if you run into problems. This job can seem daunting and WILL get frustrating at times, especially with the install! I recommend using water pump gasket seal, a red tacky substance that needs to be spread lightly on the surface of where you mate the water pump gaskets to the pump. It helps with the installation and keeps the gaskets from moving. DO NOT USE RTV GASKET MAKER or any silicone based! Coat your water pump bolts and threads with the water pump gasket sealer as well to keep coolant from running out the bolts when the engine heats up. It will save you frustration and keep your Optispark safe.

There is much I am trying to remember but as I said, let us know and I will get back to you as soon as I can.

 

Thank you for the advise. I was going to replace the seals. I think there is 3 behind the opti and water pump. I have to look up them. I never heard of removing the power steering pulley until you just mentioned it. But that's really good information too!
I'll let you know how I make out.

 

OK so my shopping list consists of
New Opti
New water pump
Jug anti-freeze
Thermostat gasket
balance puller
power steering pulley remover/installer kit
Seal,Water Pump Drive Shaft
Distributor drive Seal
Water pump gasket sealer
Am I missing anything?

 

I have had my opti off a few times and never have I needed to remove the power steering pulley. I use a short socket with an extension. That allows me to get to the bolt head. The pulley may be in the way of the socket for the final threads, but you should be able to turn it out with your fingers. Install would be reverse order.

Just try it yourself before removing the pulley.

 

Before you buy the PS pulley puller, see if you can get a socket on the semi-hidden bolt. Its hard to get to, but if I recall correctly from 18+ years ago (old age is taking its toll), if you use a 3/8" ratchet, with a 6" extension (smaller diameter than a 1/2" extension), and a short socket, you can just edge past the pulley. If that fails (maybe there are subtle differences between my 94 and a 97), look to see if it might be easier to loosen the two bolts that hold the PS pump, allowing the pump to be moved slightly to the side.

You need thread sealer for the water pump bolts that go into the water jacket.

There is no separate gasket on the thermostat housing. The seal is make by a rubber O-ring that surrounds the edge of the thermostat. You need two water pump gaskets, if they don't come with the pump.

You don't need to pull the complete damper (its not a balancer) off the crankshaft (unless you want to replace the crank seal as well). You need to remove the 3 bolts that hold the pulley/damper on the crank hub. It may be hard to get the pulley off the hub - its not an interference fit, but rust may make it difficult. Shoebox shows how to use a 3--jaw puller if necessary. Do not try to remove the pulley by hitting it, or pulling on the outside edge of the pulley. You will damage the rubber ring that hold the inner and outer damper steel rings together.

Shoebox has a lot of useful info:

Cam remove/install procedures - they cover removal of the water pump, Opti and pulley/damper

4th Gen LT1 F-body Cam Removal
4th Gen LT1 F-body Cam Install


Picture of LT1 thermostat, showing rubber ring

http://shbox.com/1/tstat.jpg


Water pump and Opti factory manual diagram

http://shbox.com/ci/water_pump.jpg
http://shbox.com/ci/opti_mounting.jpg


Damper/Pulley removal:

http://shbox.com/1/pull_pulley.jpg

 

I really appreciate the comments thank you. Hopefully tomorrow will be the day, I will update!

 

I forgot to add 1 more comment.... it really would have been a good idea to find a way do the final verification check involving the voltages on the Opti connector and the ICM connector. And to inspect the connectors for bent pins, corrosion, and other damage.

 

I'll check the pins on the ICM connector tonight. That is a good point. But I feel that they way it happened was the Opti failing. Just because it was running fine, then would start stalling, now won't even start. I have the coolant drained and the hoses loosen off. and the coil and ICM out of the car so it won't start now for sure, lol

 

5 hours later and she lives!

Thank you all that supplied great input

 

I am glad you got her back up and running! The feeling is wonderful isn't it?!


You can cut out your own with gasket maker sold by Autozone. It was a royal pain to trim and get my cut-out to fit the housing but I am glad I did it when I had to replace my thermostat. No leaks with the gasket sealant!

 

The rubber ring on the LT1-specific thermostat provides a perfect seal. You should not need sealant or a home-made gasket. Mine hasn't leaked in 25 years. If you buy the wrong t'stat - one for a Gen 1 SBC - it won't have the rubber ring, but it also isn't the correct t'stat.

All clearly shown in the Shoebox link above:

http://shbox.com/1/tstat.jpg

 

Sorry to hear you are having problems, it may be pointing to the Opti Spark unit, I have not read all the answers to this thread. Good luck