I keep blowing the 20amp Start/Fuel fuse and the car won't start. I've replaced it before, and the car will start and run for a week or two, then blow the fuse again. I replace it again and it may work for a few days before blowing again. Then i've had to replace it a couple of times a day to drive. Now it blows several fuses and will not start at all. I was hoping problem was just a loose or coroded wire at the fuel pump but wires are on and appear in good condition, HELP. Why does my car keep blowing this fuse?
If that fuse is for the automatic shutdown (ASD) relay, it feeds the ignition coil, injectors, alternator field, and oxygen sensor heaters. The most common cause of a blown fuse is shorted wires at the oxygen sensors, particularly if the harness fell down onto hot exhaust parts.
If the wiring looks okay, the goal is to get it in the bad state and stay that way so you can diagnose it. Don't wiggle wiring harnesses around in hopes of getting it to not blow another fuse because then there's no defect to find.
Once it is in the defective state, insert a pair of spade terminals in place of the blown fuse, then use a pair of jumper wires to connect them to a 12 volt light bulb. A brake light bulb will work fine but a head light bulb is better in this application. When the short is present and the circuit turns on, the bulb will simply be full brightness and it will limit current to a safe level. Now you can go around and unplug things until the light becomes dim or goes out. That's what will happen when you unplug the shorted item.
Note that if this really is the ASD circuit, the relay only turns on for one second after you turn on the ignition switch. It won't turn on again until you are cranking the engine. That means you'll have to bypass the relay to troubleshoot the circuit. If you want to pursue that, I'll post a drawing of the relay terminals and tell you which ones to jump. You can also pop the cover off the relay and install it that way, then squeeze the contact.
March, 3, 2011 AT 8:36 PM
Thanks for the info, please post the drawing
March, 3, 2011 AT 10:18 PM
Depending on which style relay you have, jump terminals 30 and 87 together or the two with the arrows. I use a stretched out paper clip but you can use any piece of wire. A head light bulb in place of the blown fuse will let about five amps flow. The paper clip can handle that without getting hot. A brake light bulb only draws about one amp.
If the bulb is dim when you do this, you may indeed have a separate fuse and relay just for the fuel pump. In that case, jump the fuel pump relay the same way instead of the ASD relay. That one also only turns on for one second until you crank the engine.