Fuel pump doesnt prime

[twiztidglory]

I have a 3.8 2012 and I have noticed recently that it is hard to start after if has been sitting for a few hours. With the key on engine off and the clutch in I dont hear the fuel pump priming. But it will start once I crank it over. I think the fuel pressure bleeds down after sitting and takes a second for it to build up which is causing a hard start. I have been looking but I wasnt sure if this is normal. The car drives fine.

 

[mikec]

Not sure how Hyundai does it on the coupe models... on many cars you won't hear the fuel pump run with the key ON & engine OFF. Pretty much all fuel injected cars have some "kill" logic on the fuel pump power to make sure the pump doesn't run if the vehicle has been in an accident with potentially busted/leaking fuel lines. Those strategies include:
1: Many ChryCo/Jeep vehicles and other brands run the pump for about 2 seconds when the key is first turned to ON - enough to prime the system - and then run the pump once sensors indicate the engine is actually turning.

2: Some vehicles run the pump when the key is in the START position, and then keep the pump ON when the computer knows the engine is turning via cam or crank position sensors, monitoring ignition pulses, etc.

3: Some vehicles won't run the pump until a specific sequence of engine sensor outputs are detected, typically seeing one or two pulses from the cam or crankshaft position sensors. These cars often crank for a second or two before starting, like an older carb'ed car that sat for a while and the gas in the carb had evaporated.

4: a dirt-simple technique (Ford used this for a few years, I'm sure others did as well) is to include a pressure switch in the engine oil system. As long as the engine is running there is enough oil pressure to close the switch which in turn feeds power to the fuel pump. Such systems typically also supplied power to the pump with the key in the START position since oil pressure is darn low while cranking.

Many fuel injections systems attempt to trap pressurized fuel in the system when the vehicle is turned off: the injectors are all shut (since the engine isn't running) and a check valve at the fuel pump outlet prevents fuel pressure from backflowing through the pump. These check valves often fail after a few years leading to longer and longer cranking times since it takes a bit of time to build the fuel pressure back up once it's bled down. Cars with dying check valves will often start quickly when restarted an hour or two after being shut down (a slowly leaking check valve won't have let too much fuel pressure bleed away...) and will crank for a much longer time after sitting overnight or for a few days.

My 2009 4.6 sedan (~33K miles) has the pushbutton start; it's never failed to start on "one push" but there is some variation in how long it cranks before it actually catches. It varies from a fraction of a second if I've driven the car recently, to maybe half a second if it's been parked a day or two. So I'm sure some of the fuel pressure is bleeding off but it's been pretty consistent since the day I bought it new. It's when you notice it takes longer to get the vehicle started that you need to be concerned - that means something has changed and is likely dying.

mike c.