Starts sometimes

[histapp]

My 2001 has a starting issue. About 50 percent of the time I turn the key and it starts right up. The other half of the time I turn the key and hear a humming sound from some kind of vacuum motor attached to the passenger side engine compartment. If it makes noise the truck will not start without a jump from my battery charger. Does it hum because of low voltage, or do I have low voltage and that makes it hum. If the heater fan or other accessory is in the on position when the key is turned on it usually will not start and the batteries pull down really fast. Dash guage shows alternator with normal output. I am thinking some weird random occurring power drain Please help thanks

[mschn99]

the humming noise is just the vacume pump. Its normal for them to come on if the truck has sat for a while. In no way would this affect it starting.

Have you tested your glow plug relay??

[histapp]

That pump sometimes runs on hot startups, maybe after hot engine has set for only 5 minutes. If it does not hum the engine will allways start, but if I turn the motor over and I can hear it the motor will not start and I can not detect any pattern for if it will or wont do this thanks

[silverF250]

Sounds like you have some sort of constant draw, how old are the batteries? Did you check what marc suggested?

[redstroker_2002]

check your batteries sounds like low batts

[histapp]

The batteries are always low. I put them in about a year ago. A couple times when the vacuum pump was running with the key on I got ahold of it and wiggled it and it stopped running, so another time I did the same thing and it stopped running that time too. Would that indicate an intermittent leak in a vaccuum hose? I still can't make the connection between the pump running with the key on and the engine not starting.

[pipelayerjdh]

PSD's need over 10V while cranking to fire the injectors, so a weak battery that will turn the engine over may not be enough to crank it.