I have a 95 chevy 1/2 that is my mud truck. Had a 350 tbi in it. Pulled it out and swapped in a 97 vortec 7.4 with a 4l80e tranny.Put a new vortec big block fuel pump,got 65 psi to the rails. Replaced the oil pressure sensor that I broke when it was installed. New crank sensor also.swapped the wiring harness in. The truck starts right up no problem. Sounds healthy. But as soon as I stop cranking the key, it shuts off. Cuts out. I had it running for 5 minutes when I pulled the relay for the starter,so I wouldn't burn the starter out. But I had to hold the key forward the whole time. Any ideas?

 

I would look at the VATS. Which computer are you running, the one from the 97?

 

Yes i am. Complete harness swap over.

 

I don't believe it would be a VATS issue as usually that kills the fuel pump. I would say your 12v switched is suspect as you clearly have cranking voltage.

 

That right there says ignition switch to me.

 

Nope! It's the oil pressure circuit. The computer thinks the truck has no oil pressure and is shutting down. I'm assuming you have access to schematics, looks at the oil pressure circuit and trace how yours is set up. It will do EXACTLY what you're describing.

 

That would make sense. IIRC, the LT1's are wired the same way with the oil pressure protection circuit. It'll crank but won't stay running unless it senses pressure from the OPSU.

 

No, they're not. I broke mine installing the engine once but it still fired right up.

 

Is the l29 a good candidate for a 2nd gen f body project or should I forget about it and move on. Some guy is selling a truck with the engine no trans for 599. I was gunna convert to carb and go from there

 

Heads suck, but there is an aftermarket.