1G 20A MPI fuse keeps blowing

[DeadlyScone]

I have a fuel pump re-wire, AEM WB simulating 02 sensor, and DSMLink v3 full, and HKS full auto turbo timer. I haven't had this issue in a long time (4-5 months) but my MPI fuse keeps blowing. I can start the car and drive it for a couple mins and it blows the fuse.

The first time it did it 4-5 months ago it blew and I replaced it and it didn't give me a problem. It happened tonight on the way home and replaced it, drove 2 miles, parked, started it then drove for a couple mins and it blew and now it just keeps blowing quicker. Side note I was getting a DTC for 0021 (Engine coolant circuit malfunction) and I have had to redo some wiring at the connector for the temp sensor on the thermostat housing. The DTC is not on anymore.

What can cause it to blow?
Does it have to be within the MPI circuit?

 

[stars]

Try this first. Find and unplug the M.P.I control relay, with relay unplugged check to see if it blows the fuse, the fuse that blows is it #1 10 Amp fuse? Located inside under drivers side kick panel in that P.D.S? Go back and check over that fuel pump re-wire, if it that fuse and it keeps blowing. Also swap out M.P.I relays if you have a spare one around.

That is the easiest first to do for troubleshooting this problem. Keep in mind there is fuses #19 10 Amp, Fuse #11 10 Amp and Fuse #4 10 Amp fuses involved in the M.P.I circuit diagrams. It would help to know which fuse Number you are frying in order to help further troubleshoot.

 

[DeadlyScone]

Try this first. Find and unplug the M.P.I control relay, with relay unplugged check to see if it blows the fuse, the fuse that blows is it #1 10 Amp fuse? Located inside under drivers side kick panel in that P.D.S? Go back and check over that fuel pump re-wire, if it that fuse and it keeps blowing. Also swap out M.P.I relays if you have a spare one around.

That is the easiest first to do for troubleshooting this problem. Keep in mind there is fuses #19 10 Amp, Fuse #11 10 Amp and Fuse #4 10 Amp fuses involved in the M.P.I circuit diagrams. It would help to know which fuse Number you are frying in order to help further troubleshoot.

the 20amp mpi fuse. The one on the battery cable.

 

[stars]

O.K. found it. it is Fuse #1 20 Amp Fuse; Black/Red Wire coming from battery and going to Pin #10 @ the M.P.I relay. Output from Pin #4; Red Wire outputs to Pin #107 @ the E.C.U. It supplies power to the E.C.U thru the M.P.I relay. Either it is going to be a relay problem or E.C.U problem is the cause. Check the wiring for continuity at the Pins, and check all connectors for proper connection.

The best i can do is narrow it down to 1 of 3 causes.

#1 Wire short to ground
#2 M.P.I Relay faulty
#3 E.C.U internally shorted

Only way to troubleshoot from here and find out the cause is to unplug the M.P.I control relay and the E.C.U. Figure out which one blows the fuse when you plug them back in. The proper test equipment from here will be needed before you can troubleshoot any further from here; if what I have mentioned has failed to find the root cause of the blown fuse.

Side Note: Since you have had the problem before and it went away, and now it is back there is a very good chance that the problem is in the wiring. Continuity test of the wiring will let you know if my guess is correct.

 

[DeadlyScone]

Thanks. I'll look into it.

 

[wrencher]

The 20 amp fuse supplies power to multiple components.
The MPI relay is the "switch" that controls the power flow to these components.
The relay is activated by the ECU to turn on pretty much all 12 volt/battery voltage powered engine control component under the hood.
The MPI relay is a dual relay, with one part doing the function above.

The other part of the relay is fuel pump control. (this is not part of the MPI/main 20 amp fuse's circuit)


Follow the power flow through the relay, once activated the fuse sends power to (in no particular order);

waste gate solenoid
idle speed control motor
mass air flow
ECU (key on system power input)
fuel pressure solenoid
EGR solenoid
purge solenoid
fuel injectors (power to resistor pack)
oxygen sensor (power to heater circuit)
crank angle sensor

My bet is there is a harness issue.
Possible one of the above components is causing a intermittent short,also.

Print these 2 diagrams too, to help guide you along to find the short.