Hard start at operating temp.

[icthus]

My 780 Bertone, v6, is causing me some greif. I finally got it running pretty good, O2 sensor was the main problem but the cat was clogged. good thing they are ceramic. Flushed it out and let it dry by slow moving compressed air. Cat flows wonderfully now. Now for the main issue.
when I start it in the morning if fires right up. No excessive cranking. After it runs for 10 minutes or so the problem starts. If I shut it off then try starting it again it takes roughly 10 seconds of cranking before it tries. It will start, run rough for 4 or 5 seconds then it's back to normal. I've cleaned the Mass air (correctly), changed the fuel pressure regulator. I know that more than likely isn't it but it's better to give more info than not enough. New in tank fuel pump. Both pumps are working fine.

I drove it about 330 miles friday and it ran fine. Shut it off and back to the long cranking.

I'm at a loss here. Coolant temp sensor is new too. What could it be?

thanks in advance. I really appreciate all the help you guy's give.

Casey

[jimmy57]

Retained fuel in fuel lines and fuel rails at engine is held by FPR and the check vsalve in the main pump. Pump can pump fuel perfectly but not keep it from back flowing to tank. Check fuel pressure runiing and then monitor when you shut off engine. Should hold at least 150 kPa/22 psi for 20 minutes. IF not repeat test and immediately after shut off use needle nose vise grips to close rubber hose behind main pump going back to fuel tank. If it holds pressure you have a 100% proof of fuel pump check valve.
When cold there is no heat in fuel lines at engine to vaporize fuel so fuel pressure loss like this usually has liitle or no cold start symptoms.
Could also be a leaking injector.
IF it is a leaking injector you could have the same symptoms but when it does start after long cranking you'd have black smoke discharge and it will run roughly for a minute or so until it clears the flooding out of the cylinder with the leaking injector. Other cylinders get vapor flooded with the affected cylinder getting the liquid.

[icthus]

Thanks. Won't the pump preload the fuel system? I'll check it anyway. Stranger things can happened.