The problem with using a bike pump is that the volume of air that comes out is very small. So even the smallest leak will just bleed off any pressure you can build with ease. I would highly highly highly recomend using an air compressor. One that shuts off when it is full, so you can hear for leaks. In the absense of one of these, a 3-5 gallon air tank from walmart will work. Go down to the gastation or where ever, fill that bitch up, and take it back to the car. Pain in the ass, but cheaper than buying a compressor if you dont have one and none of your useless friends have access to one
Edit> With really big leaks a compressor may not even be able to keep up, because of the restriction caused by the shrader valve (valve stem type valve). My current leak tester has an airline fitting on it, one of the quick disconnects you put on all your air tools so you can swap them out. I fill the 6 gallon compressor and let it shut off so its quiet, turn the output regulator all the way down, connect that hose, then gradually turn it up to 20 psi or so. Even a massive leak will become readily apparent since there is such a huge amount of airflow available with this tester setup. Intake pressure testing, POSr Stylee.