I drove about 158 miles at 2500RPM with the AC on from Columbus yesterday. I have no DTC's. The wife and I arrived at our destination and shut off the car. The car ran perfect, as always. 1.5 hours later, we come back to the car and it will not start. It turnes over just fine, and once in a while it back fires like a shot gun ,but it won't start up. So I called dad and we trailered it home.
Here's what I've done last night and this morning and the car still won't start:
---Plugs were fouled (2weeks old platinums gapped at .050), so I changed the plugs and put a new coil on it just since I had never replaced it before.
---Put a gauge on the shrader valve
---It read 20 or so when I turned the key and prime the pump
---It reads and holds 43psi when I turn over the engine.
---Opened throttle body
---Seems to be excessive carbon/oil buildup in the intake
---PCV still rattles
---Cleaned air filter.
---Checked for spark (only pulled one wire)
---spark was orange and not blue
---I suspected weak spark and replaced coil
---Pulled o2's, they're literallly, clean as new
---Tried to start car
---No start. just turns over and pops a little.


I'm clueless because this car hasn't missed a beat in 3.5 years (35,000 mi). The opti was replaced with the cam about 25,000 mi ago.
I just had it on the dyno for some tuning on friday. All I changed was MAF calibration for equivalent RPM range of 3400-6800RPM--Not cruising RPMs. The car had been running 13.8:1 AFR at WOT so I bumped it down to 12.4:1 and made 349 ft.lb of torque and 308 hp. I don't believe this has anything to do with the problem since I drove it all saturday and again sunday morning.
I have class tomorrow back in Columbus (Finals are next week!) and have no car unless this runs...please help! If any other info is needed, ask. I'll be around all day.

 

sound like opti

 

even though it didn't sputter or miss while it did run, you think it is opti? Opti seems like the next link to check but it just seems odd that it would instantly stop working. It has not been driven in the rain nor has ANY water been in that area. A local guy here who builds race motors and owns a shop thought it sounded like the timing is out of sink. He does not have any experience with the LT1 but wondered if we had a cam position sensor or crank sensor that may have failed.
Am I correct in saying that we have a cam sensor and not a crank sensor?

 

Verify that the coolant sensor in the waterpump (the one the the PCM reads) is working. Also might see if it starts by holding the gas pedal to the floor (flood mode).

 

No crank sensor and no cam sensor that I know of. Unless there is one in the opti itself. It does sound like a timing deal, but that's either the chain or opti. Maybe an ignition switch? I'm just throwing ideas out there.

 

The cam and crank sensor are functions of the optispark.

 

I'm pretty sure the OBD2 cars came with Crank sensors and maybe the OBD1 cars did not. A guy brought his Snap-on diagnostic tool in case it offered help over freescan and datamaster and found nothing. He did however offer knowledge from some classes he went to years ago when these motors came out. Apparently an engineer from the manufacture taught the class and stated that if the crank sensor goes bad while driving, the car will die immediately, but if the cam position sensor goes bad while driving, the computer will still know where it's at in the timing and continue running the engine, but once you shut off the engine it will fail to restart until repair. It makes sense to me, and he further believed this to be the problem after I told him the car ran fine before I shut it off.

I searched and found an optispark thread defining the two major causes of failure as: (1) Water in the optispark (not in my case) and (2) High RPMs causing things to break apart in the opti, in which case the guy stated he has to replace his once a year (rotor only). Considering my dyno runs Friday night, if (2), above, is true, then I believe this is my problem. I lost the thread concerning this, but can anyone tell me which part it is in the opti that would break apart from high RPM's? Is it the rotor? If so, is the MSD one made of materials which will better withstand the high RPM?
I would like to minimize my probability of failure by replacing the broken link with a stronger one.

 

I thought 96-97 had a crankshaft positioning sensor on the bottom of the timing cover?

 

I know the 96 GS LT4 Vettes had a crank sensor, but I'm not sure about the 96-97 LT1's.

 

The crank position sensor in the 96-97s has nothing to do with spark delivery. It was only put there as an OBD-II requirement for misfire detection. If it was broke or even totally missing, the engine would still run (not the same as most other cars that use a crank sensor).

So...for spark delivery purposes, the opti does all the crank and cam position sensing.

 

Well I know my 97 SS does. Cuz I replaced it right before I started driving it.

 

Come to think of it I had a car in the shop a couple weeks ago that kinda did the same thing. It ran good all night and all of a sudden it died and wouldn't start at all. What happened was the rotor came loose inside the opti and fell off its mounts. Didn't hurt anything, but it wouldn't run at all.

 

I'm willing to bet that as soon as we get this pulled apart, it will be the same case. So was the opti repairable with a new rotor or did you have to put a new opti on?

Does anyone know about the new Accel optispark offered in Summitracing? I will make some phone calls this week to Accel and MSD to try and get a technical person on the phone. I want to know if they've used stronger parts so the rotor does not come off.

 

I've had that pile come aprt on me too, but who hasn't.

 

def not something you want to happen 158 miles from your house!!!!!!!!


im taking a trip this summer, btch better not leave me!!!!!!!!!!!!! Keep us posted on what you find!