My 99 Honda will not start after being driven for a while. It will turn over but not hit. After 15 min it will start. It always starts the first time if try it with no problems. What could it be?

 

It could be fuel vaporizing in the fuel rail. It usually happens in the transition from winter to summer fuel supplies. The winter type vaporizes more readily. With that type of fuel in hot weather, when you shut off the engine, the rail heats up, fuel vaporizes and the result is similar to vapor locking.

If you crank the engine over several times it purges the vapor in the rail, brings in liquid fuel which the injectors can work with and the vehicle starts.

Another possibility would be an ignition module or coil/coil pack that acts up when it gets hot.

Hope this helps,

Bob

 

Basic first step - narrow it down to fuel or spark. When it won't start pull a spark plug wire and check for spark. Got spark, continue troubleshooting fuel system; no spark, work on ignition system.

 

turn the key on don't crank, turn off for 30 sec, then on again, due this about 3 cycles when it doesn't start, if it is vapor lock this should build enough fuel pressure to overcome the vapor lock. when you pull a plug wire use a old spark plug in the wire touching ground to test for spark.
life begins when the kids leave home and the dog dies

 

Do you have a check engine light. While I would not rule out the vapor lock scenario (a very good chance), it sounds like something that happened with one of our cars when the temp sensor went bad. When the car was warm, it still thought it was cold and thus flooded the engine out when we tried to start it hot. We could get it to start if we let it sit OR if we floored the gas (just as you do with a flooded vehicle).

It could be a few other things as well.

 

vapor lock is more a thing of the past. it's caused by fuel being boiled in the fuel line or float bowl on carbureted engines...this could be caused by high under hood temps during a hot soak or if a fuel line was actually touching hot engine parts.

fuel injected engines, for the most part, maintain some pressure in the fuel line after shutdown. the positive pressure in the lines raises the boiling point of the fuel just like the pressure cap on your radiator raises the boiling point of the coolant. not only this, but the boiling fuel has no where to go, unlike carbureted engines, fuel boiling in the fuel line would relieve it's pressure into the float bowl.

while boiling fuel in the line may be a potential cause of your hard starting problem...i'd concentrate on doing as tow_guy said...take it out and make it happen, then test for lack of spark or lack of fuel (whether it be lack of pressure or lack of injector drive, that's still a fuel related cause). you have to separate the 2 first and then you can concentrate on the actual cause.

turning the key on and off a few times may tell you something about the fuel system...but installing a pressure gauge will tell you more.it would be nice to know if the pressure drops to zero as soon as the pump quits running...