hey guys,
my 16 year old son has a 1994 Camaro z28 that we rebuilt for him. it is a work in progress. 188K on the body, but 92K on the engine we installed. when i installed the engine, i installed new plugs, wires, Opti spark, coil, water pump, alternator, ac compressor, new belt new fuel pump and few misc. pieces. he has been driving it since January. it runs great, but now have the problem that every once and a while, it won't start. you can crank and crank and crank, and it won't start. come back out there an hour later, and it will start. there is no rhyme or reason. it has done it twice now in last week. i thought it might be the ignition control module when it threw the fit last night, so i changed it , and it still wouldn't start. came back out an hour later and fired right up. i did test for spark, and when it doesn't start, no spark. anyone else have this problem? i am at a loss.

 

Does the "SECURITY" light stay on after the initial 3-second "bulb check", in cases when the engine does not start?

Have you scanned for codes? DTC 16 sets if the PCM does not see the low resolution cam position signal from the optical module in the Opti. DTC 16 shuts down the fuel system, and does NOT turn on the SES light. Additionally, the code can't set if the high resolution pulse signal from the cam position sensor is also not detected, and engine will not start. Even if the high res pulse is present, the PCM requires an extended cranking period to set the code.

Check to see if the cam position signals are reaching the ICM:

4th Gen LT1 F-body Tech Articles

What brand was the Opti you installed? Most of the ones available presently are cheap, unreliable Chinese junk. Even the expensive MSD can be a problem, depending when it was produced.

 

the opti, spark plugs, wires, coil, and icm are less than 3 months old. I had a problem with the passlock system a month ago but bypassed with a resistor. I don’t remember what brand optispark it is. It was off rockauto. I didn’t go cheap. These cars have a cam position sensor or crank position sensor? Like I said it has only pulled this stunt twice in last week where it won’t start. Then you go out couple hours later and it will fire right up and be fine for a few days

 

94 LT1 only has a cam position sensor in the Opti. But the pulse signals are encoded to identify which cylinder is approaching TDC on the compression stroke. If effect that is a pseudo crank position, and the PCM knows the position within 1°. This approach provides extremely precise spark and injector timing. That allows for more ignition advance, due to reduced spark scatter. Also reduces emissions.

In 1996 model year they added a crank position sensor to the LT1, but it is only there to detect misfires as required by OBD-2. It is not used to run the engine, and if it fails will only eliminate misfire detection.

Not uncommon for the Chinese rip-offs to be bad out of the box. Outfits like Cardone and AIP appear to sell this stuff under their brand name. The fact that an Opti is only 3-months old does not mean it can’t be failing.

 

I just looked. It is a cardone brand optispark

 

When it's not starting, you need to do the test I linked in post #2. If you don't have the correct voltage on the white wire from the PCM to the ICM pin B, you won't have spark. The PCM uses the Opti cam position lyses to determine when to tell the ICM to fire the coil.

If it fails the first part of the test (ICM Harness), proceed to the second part of the test (Optispark Harness). This checks to see if the PCM is providing the Opti with the reference voltage it requires to produce the cam position info. If the PCM test passes, the Opti is the problem.

Last step would be checking the actual pulses from the Opti, but that is best done with an oscilloscope.

A quick check of the Opti harness connector for corrosion or pin damage, and a check of the harness wires for damaged insulation is worthwhile.

 

well i tested everything and it pointed to Opti spark. i wasn't getting the 1 to 4v ac from PCM to igntion control module, so i changed optispark. still no start, and no spark.

 

Did you do the second part of the test (as I recommended) to prove the PCM was providing the Opti with the 12 volts is requires to operate, and a 5 volt reference voltage for each of the cam position signals? Did you inspect the wires and connectors for damage (as I recommended)?

What Opti did you install? There are only two sources that are currently recommended - Petris, and AC Delco reman. Most others, particularly the cheap Chinese junk they sell on eBay, or the rebranded stuff like Porter or AIP are unreliable and can be faulty when you take them out of the box.

 

yes did all the opti test and just bought new cardone optispark in there yesterday. All the wires check out for optispark

 

When the Opti is off the engine, but still connected to the wiring harness, key on, you can test it for the high and low res pulses, simply by turning the drive shaft slowly and looking for the voltage to switch back and forth between 0 volts and 5 volts.

Cardone is not a reliable unit.

 

this optispark tests out fine. it is brand new out of the box.

 

How did you test it? Did you test the old one in the same way, before discarding it?

The only other possibilities at this point are a failure of the white wire from PCM pin B5 to IDM pin B, or a PCM failure, which is rare.

 

I tested same way as old one. Per shoebox diagram site

 

But no part of Shoebox's test procedure actually tests the Opti. As he mentions at the very end, you need to test the Opti with an oscilloscope. I mentioned that in post #6. Since that's not something most people have in their tool box, the alternative way is the one I just described, with the Opti off the engine.