scotts492000

I have a 99 K2500 Sub with a 454 with 95,000 miles , Im trying to figure out a hot start problem , Im a mechanic by trade so Im not new to this but it's driving me crazy . The engine starts fine when cold runs great , no codes , When I drive it and get it hot then shut it off and let it sit for an hour or so sometimes when it starts the idle goes up and down - surging between 400-600 rpm then clears up and runs fine . If it sits for less time it's fine . It's intermitent . It's not blowing black smoke on start up when it does it - Im aware of the origanal injector issues . I have installed Bosch 19lb yellow top injectors 4 years ago to solve that issue , In the last year I have changed out , Plugs, wires , fuel pressure regulator, complete new distributer, new cap and rotor , ecm coolant sensor , egr valve, IAC valve , New upper and lower intake gaskets , 4 new o2 sensors ,Delco fuel pump 3 years old with 12K miles on it , Fuel pressure @ 60-63 psi running , holds 45-50 psi over night . Cleaned the throttle body , Ive done the crankshaft camshaft correlation re learn with my scan tool , crank retard set at 0 degrees , It really only has this issue in the summer , winter it's fine , The only thing I cant rule out is vapor lock when it sits when parked hot . I have a Maxdius scan tool and everything checks out . Im out of ideas . Im AZ we have 10% ethanol blended gas that may be the cause ? I really think the fuel in the rail is boiling when it sits when it hot , I would like to hear any ideas you have on this .

kevinkpk

I don't think the fuel in the rail is boiling. Has there been anything done to the fuel lines?

scotts492000

No modifications to anything , all stock .

kevinkpk

Vapor lock can happen with fuel lines routed too close to a heat source, and or tight bends. This is factory, so therefore I cannot see that being the issue, same with the fuel rail. You also have a pusher fuel pump, not a puller (mecahnical) pump drawing gas from one end to the other. Only thing at this point I'd suggest is pull the fuel line off both ends, and with compressed air blow the line out. I have had experience with "older" cars with puller (mechanical) fuel pumps do what these same symptoms are, pin hole in the gas line. Pulling air into the fuel line.