I have a bit of a problem efi fuse blows when turned to ON position

 

my battery/ brake light came on while driving home , checked it with multi-meter it was getting 16.5 to battery terminals. next day drove vehicle into my garage. replaced alternator. went to crank vehicle it will turn over but wouldn't start. found EFI 15 amp blows when turned to ON position. I checked O2 sensor appears fine but disconnected anyway, still blows fuse, looked for dead shorts none found yet. disconnected air flow meter still blows, disconnected COR and LB1 still blows, if I unplug CPU it doesn't blow. more tinkering and found if I have everything hooked back up except last port on CPU it wont blow . that port is closes to passenger door. Stumped

 

Did you check the wiring to the O2 sensor connector? This wiring often rubs and melts on the exhaust causing a short.

The EFI fuse connects to the BATT terminal on the ECU. This terminal is on the ECU connector closest to the passenger door.

 

I checked O2 good and took insulation off! no burnt spots on wires, I separated them from each other. I have removed every connection from transmission to fuel rail and lefted them disconnected , turn key to On it blows if EFI fuse. If I disconnect ECU last port it doesn't .I have a power probe coming to help look for dead short . it has me on the ropes right now

 

I jumped a headlight to the EFI fuse spot and it shines bright and wont go off when I unhook components are shake wiring harness. Which if I am right means there's a dead short ??

 

That depends on how exactly you hooked the wires up when you did this test. More detail is needed.

Did you connect both fuse terminals into the headlight, or just the positive into one terminal?

I hope you had the ECU disconnected when you did this test. You don't want to bypass a fuse with a headlight. Depending on where the short is, it may allow too much amperage into the ECU.

 

ecu was disconnected. I used a low amp light 12v, it was in fuse slots. didn't use more than 2 mins. felt is was wasting time

 

I believe power probe will assist me a little. I am going thru every wiring harness on engine section first, removing flex tubing a checking all wiring and connection while I have it top side. nothing is hooked to engine components/ sensor, except starter.


if its in the harness that leaves the fuse box that travels to injectors, sensor,transmission I should find melted are bare wiring.

 

Did you have the ignition on? If it was the light could be grounding out through another component such as the Circuit Opening Relay coil.

If you remove the EFI main relay and redo the test, that would help narrow down the problem area. With the EFI main relay removed (and ECU disconnected of course) the light should NOT illuminate when the ignition is on.

 

will do tomorrow, decided to get nasty outside. I will let you something

 

EFI relay removed and ECU disconnected light didn't illuminate when ignition in ON position

 

Sounds like the short is downstream of the EFI relay. This circuit goes to several components with the previously mentioned O2 sensor wiring being the most common problem area.

I would unplug all 3 of the ECM connectors, unplug the O2 sensor, remove the EFI relay and see how much resistance you have between ground and EFI relay terminal 3. This is the relay socket terminal that has a white wire with a red stripe. There should be infinite resistance between ground and this relay socket terminal.

If there is any continuity with ground, that verifies a short. You may have to jiggle wires while someone watches the multimeter to figure out where the short is.

Just remember to remove all the ECM connectors and O2 connector so the multimeter will not find continuity to ground through one of several components on this circuit. You never want to check for continuity when the harness is hooked up to the ECM because the multimeter would then input voltage into the ECM possibly damaging it.

 

thanks! I will give it a shot tomorrow, hope I find it. update you tomorrow

 

the efi relay fuse has had some rewiring work in the past, it outside the fuse box which has nothing to do with the efi 15 amp fuse blowing, it been that way for the 5 years that I have had truck but two terminal came loose while I was searching for short. is there a diagram that shows which color wires hook to which terminal on the relay fuse or does it matter

 

The fuse doesn't care which way the current flows through it if that is what you are asking. The 15A EFI fuse should have a white wire with a red stripe and a black wire with a green strip going to it.

Alldatadiy.com has a diagram that will tell you where every single wire, splice, connector and terminal pin you can think of goes but you have to pay for it. That is what I use. It is worth it if you work on cars a lot.

 

thanks will check that out,

 

well! I have been working on this one since I got it, thought I had most of it figured out, but this electrical problem is kicking my butt

 

well! don't know if I found the culprit or a secondary fault from the primary problem. the white / black strip with red circle every couple inches, that come from one terminal off the EFI relay is burnt up good. this travel from EFI relay out of fuse panel crosses in front of radiator burnt to driver side so far. still unwrapping

 

Any thoughts?


I have been searching with battery disconnected, hooking up to perform test, then I disconnected battery, yesterday left battery hooked up, ignition off . noticed my error when closing hood for the night and disconnected battery.


this morning noticed wire melted just short of EFI relay and started tracing it out.

 

traced out the white with black strip with red dash or circles to a multi ground on drivers side under coil bolted to frame. then travels down thru fender heading to cab area, luckily it stopped where the factory attached other ground