My '88 Grand Caravan does that too. It always starts instantly in the morning, but once warmed up, it must crank about five seconds before it starts if it sits more than ten minutes. After watching how it acts for the last ten years, I figured out it's a leaking injector. In the morning that fuel in the cylinder has condensed to a liquid that doesn't cause a flooded condition. That's why it starts right away. When restarting it hot, not much fuel has leaked yet so the engine starts quickly, but longer than about ten minutes, and the excessive fuel vaporizes. That causes a flooded condition that has be be cleared out first by cranking. In addition, fuel pressure has dropped. Other than the first second after turning on the ignition switch, the fuel pump doesn't run to build pressure up until you start cranking the engine. Between clearing the flooded condition and building pressure until it's high enough to spray from the injectors, that can take a good five seconds of cranking.
There could also be a small piece of varnish or dirt holding the pressure regulator partially open. That would not be noticeable while driving, but fuel pressure will drop off instantly when the engine is stopped, and it will take a long cranking time to build back up. That can be intermittent depending on how the valve seats when the engine is stopped. About the only way to find that is by connecting a fuel pressure gauge and watching how it responds over many days. If you do my cycling the ignition switch trick, the pressure will only build very slowly during cranking if the regulator is leaking. It will build very quickly and stay up if a leaking injector is the cause.
Sunday, August 14th, 2011 AT 6:07 AM