My '93 LT1 shut down on me the other day while I was on the highway. Everything just shut down and I coasted off the road to teh shoulder. I tried to restart the car and it started right up, just like it always does. About 3 seconds later it comletely shuts down again. So I call AAA. Then I decide to try agian, the car started great with no hesitation then about 6 seconds later it shut down yet again.

Once I got the shop we plugged in the computer and gt code 16 whcih had a reference to some connection, everything was cleaned and the connections checked. We turned the car on and it idled for about 15 minutes then shut off, this time code 42 came up. The mechanic checked into this code and restarted the car. Everything was fine for a while then it shut down again, this time no code. What gives? Is it the CPU? We took the aftermarket piggyback chip off and it made no difference.

Has anyone had this mysterious problem?

PS- I didn't think this was related at first but who knows...last week my 'brake' light came on and when I depressed the brake pedal it dropped to the floor like it had lost pressure. I pulled over and checked the master cylinder, everything checked out ok. For 4 more days the light remained on but the brakes works perfectly. Then Monday when I started the car up I was expecting the light to come like had been for days, but it never did.

So I think it might be th CPU meesing things up.

 

mine started doing that before the opti died.

 

On my 93Z, it was the OPTI........

 

The tab in the rotor of the opti usually gets a hole worn thru it at around 90k miles. When that happens it acts exactly as you describe.

 

The 16 is a loss of low resolution pulses from the opti. This signal tells the computer where the mechanical rotating assembly is to reference fuel and ignition. When it looses this signal it is catostrophic and the PCM shuts off the fuel pump and injectors.

The 42 is indicating that the (IC) line that "triggers" the ICM is shorted to ground. This is solely the "high" voltage side of the ignition. The 42 will cause the PCM to shut off the injectors also. Even if the 42 weren't set, the loss of the IC signal would cause the ignition to shut down anyway.

You need to focus on the connection at the opti, the ICM and at the PCM.

 

DTC 16 is the code for loss of the low resolution pulse from the Opti. When the PCM can't find the low res pulse pattern for two revs of the crankshaft, it shuts down the fuel system, including fuel pump and injectors. Could be a faulty optical sensor, or a corroded or damaged connector on the Opti, or the second Opti harness connector on the passenger side of the intake manifold.

The "BRAKE" light has nothing to do with the ECM (CPU), it has its own computer. If the pedal went to the floor, the differential pressure switch in the block on the side of the ABS unit activated, because it sensed different pressures between the front and rear braking circuits. It isn't unusual for the switch to "stick" when this happens, and eventually work its way loose under a hard stop.

Perhaps there was a problem with the ABS that caused the pedal to go to the floor, and you might be seeing some sort of a low charging system voltage, or some broken or correded engine and chassis grounds, affecting both the ABS control computer (EBCM) and the ignition system.

 

Thanks for the input, I just replaced the opti in 2005 so I hope it is a sensor or connector.

 

my 93z did the same thing and it turned out to be a bad msd coil

 

Sensor

16 = Distributor to PCM. Only 3 things here to look at. distributor, wiring or PCM.
I guess technically the optical encoders in the distributor is a sensor. Either way you still have to replace the opti if the encoders are defective.

42 = PCM to ICM. 3 things here to look at also. Guess which 3.

 

1-PCM, 2-ICM, 3-Wiring

That's my final answer.

 

I had that problem off and on for years. As I went through setups and mods, I redid grounds, swapped batteries, had 3 optis in, 4 coils, 2 ICMs, 3 computers...MSD opti, MSD coil, etc etc problem remained intermittenly. I ended up swapping out my engine harness and the problem hasnt reoccured in 2 months now.