EFI Fuse problem (1 Viewer)

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Joined
Dec 23, 2015
Threads
6
Messages
24
Location
Arizona
93 fzj80
I'm having an issue with the efi fuse in the engine compartment popping and killing the engine. I was way out on the back roads and was stranded for 2 hours with a dead cell phone and no service anyway. Finally got it back up and running got out of the nasty stuff only to have it die again on a better road about 5 miles from home. Had to leave it on side of road and get a ride. Need some ideas. EFI relay? Bad ground? It was running great all day engine just died.
 
Check the wiring to the O2 sensors. The exhaust and engine heat can destroy the protective covering and clips and the wires could be contacting the front driveshaft.
 
Don't see anything noticeable there but not sure. When I broke down the first time I replaced the fuseable links off the battery and that and a new fuse was what got me going the first time. Now the fuse pops as soon as I try to start. Could the new fuseable link still be something to look at here. I have another spare. What feeds the power to the efi fuse that would be causing it to trip? Relay?
 
Check the wiring to the O2 sensors. The exhaust and engine heat can destroy the protective covering and clips and the wires could be contacting the front driveshaft.

This and the main engine harness where it goes by the EGR are the most common. It could be a short anywhere in the engine harness. Some have had a problem near where the harness plugs into the ECU, the harness shorting on the glove box frame work.
 
Ok I will try to check those areas. in these situations would the loom on the harness look damaged in any way or do I need to just pull it apart. Is there any areas I can check continuity between to trace the issue.
 
Wire color downstream of the fuse depends on whether it i before or after the efi main relay.

Between the fuse and the relay, and for a leg from the relay to the ECU to provide constant battery + for ECU memory it is red/yellow. This wire runs across the engine bay inside the main engine wiring harness on 93-94, on 95+ it goes along the drivers side inner fender then under the dash to the ECU area. After the relay it is yellow/red and in both cases it joins the main engine wiring harness via a connector behind the distributor.

To narrow down which circuit it is see if the fuse pops as soon as you put a new one in, or waits until you turn the truck on and the ECU energized the EFI Main relay. If the latter it is the yellow/red or something downstream of it. After the IH1 connector near the ECU portions of the yellow/red circuit become straight yellow for things like the circuit opening relay (iirc)
 
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Status update
I checked the o2 wiring and is still pinned up correctly and doesn't appear to be damaged in any way. I replaced the main efi relay as it was $11 and I can always use as spare. Still no luck. The fuse blows when I try to start it up. I seem to be able to turn the ignition on without trying to start and it won't blow. I've done hunting online and I'm going to look at the fuel pump as someone else had an issue with the wires there. I'll probably pull the relay for that and see if it pops the fuse and that should isolate the problem if it's there. If that's not it I'm probably looking at the harness in the egr area.
 
Wires for the inboard O2 sensor are routed above the starter and over the top of the transmission. I know for a fact that the plastic wire loom that once shielded those wires against chafing has long been cooked to a crisp and has crumbled and fallen off leaving only the wire insulation to protect against a short on the top of the transmission. You might want to check more closely.
 
I'll check those areas. On the inboard o2 sensor by the starter is the loom on on driver side then? I did look behind glovebox but didn't know where to look so I'll take a closer look at that area. Hopefully I'm getting it towed home tomorrow afternoon after work with my inlaws truck so I can look into it at home instead of the side of the road.
 
I pulled the connector at the fuel pump to test if it would blow the fuse and ... it doesn't. I'm going to pull the pump assembly and check for issues with those wires. Could be the pump maybe? Or any wiring up to that point but I think I isolated the circuit.
 
Here it is

IMG_3429.JPG
 
The glove box thing doesn't apply to OBD rigs, only OBD2. Have you checked the harness by the EGR pipe? There was a harness clip that held it away, now most of then have broken, allowing the harness to touch the pipe, sometimes shorting whatever wire happens to touch.
 
Actually looks like a PO had had a similar issue and used hi temp silicone to cover the offending area and it wore through that too. I'm going to file down the edges of the bracket. Any opinions on the best way to repair it? Don't want to try to source a new part unless necessary.
 
I just had the same issue. Popping EFI 15amp fuse. I checked the fusible link, the o2 sensors, the harness behind EGR valve, chased all wires to ECU....

Turned out to be yellow wire on my fuel pump/sender unit. Rubbed the bracket just a tad, but that's all it takes. I just cut the wire and but an insulated butt connector on there. Good to go.
 
Mine ended up being the wire going into the main fuse box under the hood. The factor gauge wire was not big enough to withstand the heat by the exhaust manifold. I was told it was a common problem. After the wire was replaced with a thicker gauge, the problem stopped. I still carry extra EFI fuses just in case....
 
Just found the inboard O2 sensor wire rubbing on drive shaft. Took it all apart and fixed. We will see if this is it. Thanks all for the advice!!!

20253264-3012-4C8C-88FB-18A626EFBDD0.jpeg
 
Mine ended up being the wire going into the main fuse box under the hood. The factor gauge wire was not big enough to withstand the heat by the exhaust manifold. I was told it was a common problem. After the wire was replaced with a thicker gauge, the problem stopped. I still carry extra EFI fuses just in case....

That weakness is unique to the 3FEe, not a problem in the 1FZ.
 

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