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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8608
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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20 amp engine fuse keeps blowing when car starts

Customer Question

20 amp engine fuse keeps blowing when car starts
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.

Hi,

If the fuse is only blowing when the fuel pump is plugged in and cranking, and unplugging the fuel pump prevents the fuse from blowing even while cranking for several seconds, the only expectation here would be a fuel pump problem.
It is important to note that there are two ways to replace the pump... you can get just the pump motor or you can get the complete pump module assembly. This is important because we have run into issues in the past where the connector on the top of the pump module shorts internally causing problems... when this happens putting a new pump motor in of course would not fix the problem.
I would be pulling the pump module out and disconnecting the pump motor and putting a different load there (old fan motor etc) and seeing if the fuse still blows. If it does not, then the motor is at fault; if it does, then it is likely that the pump module (the housing) connector is causing problems.

If I misunderstood and the fuse only blows while the engine has been running (and of course does not blow when the pump is unplugged since the engine won't run), then more precise isolation of that circuit would be in order... specifically unplugging individual sensors and evap solenoids etc on the engine to see if the problem can be eradicated that way, indicating a shorted component.

Customer: replied 1 year ago.
The car was out of use for about 8 months as the timing belt and starter were bad. These parts were replaced about a week ago and the car was doing fine until yesterday when it started blowing the engine fuse, could there be a different load causing the problem i.e. Alternator?
Expert:  Doug replied 1 year ago.

Alternator... not likely. The only way that would happen would be if you were also seeing very high voltage (and likely would be seeing multiple other problems).
If the engine is running for a time without popping the fuse, then I would start isolating one sensor at a time (less the cam and crank, since they are required to run) and see if you can get it to not blow a fuse that way, indicating a trouble part.