1994 Z-28 cranks hard but no startin wet weather. The exhaust
"coughs" as you let go of the key. Multiple trys = same disappointing result.
The motor as been turning over first try with no problem for weeks in dry weather.
The car is parked outside and of course gets wet.
Any ideas!!?? Has anybody elsehad this same problem?

 

sounds like a fuel pump problem, have you checked the fuel pressure?

if it only happens when its wet then make sure that there is no water dripping in the engine near the computer or near the front of the motor by the distributor(opti)

 

I would like to know what you find, as I have a very similar problem. Thought it was an Opti-spark problem until I replaced it and still have problems.

 

Unfortunately I have yet to find the solution to the problem. Like you, I also have a new Opti-spark ignition system. It has been 3 weeks since the car would not start but it has also been mainly dry, no rain. I will let you know if a cause is ever determined. Please keep me updated on your situation too.
Best of luck.

 

Finally got my '94 Z28 running. Was hesitating, cutting out and check engine light was coming on once and a while. It finally died on the road, once before and once after the new Opti-spark. It ended up being the coolant temp sensor. I should have known, as I had same problem with my '91 Silverado. For $11 it is worth buying one and plugging it in to see if it starts. I dissected the old sensor to find the internal connections rusted through. I was not able to get any error codes out of the PCM, still trying to figure that out.

 

Sometimes you need to look at the sensor output with a scan tool, & see if the readings make sense. Some silly thing like ECT sensor showing -30 temp when it 85 outside.