To all, This is my first post here. My Father in Law has a 1994 Z28 Camaro with T-tops and automatic. I am quite familiar with small blocks etc. I just sold a 1968 Camaro Coup with a 523 horse 383 small block that I hand built myself. That being said, the LT1 is new to me, and this car has me stumped.

When cold, she starts right up. She runs hard and makes plenty of power. As soon as it gets warm, it would just shut off. No poor running, just shut down and wouldn't start until it was cool. My first thought? ICM, so I put a new one on, along with a coil. (the old ICM failed the Advanced auto tester High rpm after 2 test also) She idles better and pulls through a few hundred more rpm. It also doesn't shut itself off, but if you shut it down then try to restart it after 5 or so min (like getting lotto tickets at the gas station) she will not restart for 20 min or so. I have verified that when it doesn't start it has no spark to cylinder #1. I have cleaned all connections, made sure the ICM has good grease under it, tried a new ICM etc. I am stumped, what else can get heat soaked and cause no spark?

 

Have you scanned it for codes? The optical cam position sensor in the Optispark distriburor can heat soak. If it does it will set codes.

Could also check the fuel pressure to see if the fuel pump has a problem when it gets hot. But that wouldn't cause "no spark" condition.

 

Thank you, Its definitely a no spark issue. It has plenty of fuel pressure to start. When cold she throws a beautiful 1/2 long blue spark, when she will not start, its either no spark at all, or a very intermittent very weak spark that occurs once every 10 or so crank revolutions. As far as codes, The SES light is not on, and I do not have a code reader that will work with a 94. I have an OBDII scanner but not one for this 94.

I am surprised that the optical cam sensor is susceptible to heat. In the morning I will do the Opti tests with my multi tester.

Thanks again!

 

I just went thru the same problem. Its the optispark optical sensor. Just rebuilt my opti and it fired right up

 

The code that keeps it from running is DTC 16. That code does NOT turn on the SES light.

There is a link to a download of free OBD-1 scanning software in a sticky at the top of the "Computer Diagnostics and Programming" forum. Also has a guide to cables.

You need to scan it for codes before jumping to conclusions.

 

If t was my car I would jump all over the scanning software but it isn't. I am doing him a favor by fixing it myself. There is no way to flash the 94 is there? Advanced said they can only read codes that kick on the SES light (but I don't think he really knows).... I am about to have my son help me test the ignition as layed out on SHBOX.com. I will let you know what I find.

 

Can't short the ALDL connector pins to flash the codes on anything after 1993. Most auto parts stores won't even scan OBD-1 cars. And of course the SES light does NOT have to be on to scan for codes. And the scanner will pick up the codes that do not turn on the SES light.

 

Well I tested the ignition based on the procedures at the top of this forum and SHBOX. The White wire has no voltage when hot, but when cold has an AC voltage of about 4 volts. This tells me the PCM isn't sending out a signal to the ICM. Another indication it could be the camshaft sensor in the Optispark. I hate to do such major surgery without conformation but short of buying a patch cable I am not sure of any more tests I can try.....?.? Unless there is someone local with the software! (Bonita Springs FLorida) that could help another car lover out!

 

Check the signals at the gray Opti test connector on the bracket on the passenger side of the intake manifold. As you slowly rotate the engine, the signal should switch back and forth between 0V and 5V DC.

First check to see that you have 12V DC between the red wire and a good engine ground. That is the power supply to the cam position sensor.

Then work on the pulse signals. The key signal is the low resolution pulse. That would be measured between the red/black wire and the pink/black wire. The low res singal will have four variable length 5V DC pulses per crankshaft revolution. If those aren't present, the PCM shuts down the fuel system, and can't send the signal on the white wire to the ICM.

If you connect between the purple/white wire and the pink/black wire you will see the high resolution pulse, but that switches very rapidly, because there are 180 5V pulses per crank rev. If you switch the meter to AC voltage, you should see something in the 2.5V range. The PCM can run the engine without the high res pulse, with a minor loss in timing accuracy and increase in spark scatter. But nothing you would notice in the way the engine runs. Won't keep it from starting.

 

I broke down and replaced the whole optispark unit. IT WORKED! it must have been the optical sensor going out when hot.

 

typical opti problems.

someone is having this issue on a facebook forum and everyone want to argue with me that it cant be the opti.