Crank no start, everything fixes for a day

[92rcsb]

Ok, so I had a crank no start issue after some troubleshooting changed the fuel pump ant it ran great for the day, next morning didnt start again. Changed fuel pump relay and same thing ran great, next morning no start. Now I've changed fuel filter, fuel pump fuse, ign coil, cap & rotor, plugs, wires, checked for codes and got nothing but a 12 obviously while not running. After every part that I've changed the truck has ran great for a day, no issues while running whatsoever but the next morning refuses to start. I'm at an absolute loss on this thing

 

[HotWheelsBurban]

Did you ever figure it out? What did it take to fix it & how much $$? Thanks

 

[Schurkey]

Stop looking at "codes", start looking at the data stream, and the engine itself.

Do you have spark when it won't start? Do you have fuel spray/fuel pressure when it won't start? Does the fuel pump prime? What is the cranking compression of all eight? What is the cranking vacuum in the intake manifold? What temperature does the coolant temp sensor say the coolant is, BEFORE the engine starts? What is the RPM reading on the data stream when the engine is cranking?

 

[HotWheelsBurban]

What year is your truck? Might be the VATS factory anti theft system acting up, if it's 96-up. I think that is what my issue was. Finally found a tuner that could electronically disable the VATS and so far, so good. If it stays fixed it will be $250 well spent.
If your truck is 95 or older then it's not the VATS but some other electric issue. Then you have to look at everything and start eliminating parts.
That's one of the things that my truck did; start and run great all day and then not want to go the next day. All the computer controlled stuff gets finicky after 20 years or so, especially in high humidity

 

[df2x4]

What year is your truck? Might be the VATS factory anti theft system acting up, if it's 96-up. I think that is what my issue was. Finally found a tuner that could electronically disable the VATS and so far, so good. If it stays fixed it will be $250 well spent.
If your truck is 95 or older then it's not the VATS but some other electric issue. Then you have to look at everything and start eliminating parts.
That's one of the things that my truck did; start and run great all day and then not want to go the next day. All the computer controlled stuff gets finicky after 20 years or so, especially in high humidity

VATS (technically PassLock for these trucks) didn't start until '98.

 

[HotWheelsBurban]

IIRC 96 and 97 had a version of it, 98-99 is 2nd generation and the GMT 800 trucks are different yet and more complicated

 

[df2x4]

IIRC 96 and 97 had a version of it, 98-99 is 2nd generation and the GMT 800 trucks are different yet and more complicated

I have two '97s and neither of them have any form of PassLock/VATS.