So yeah I have a 93 22re, recently rebuilt the timing chain. Now at random times I think it happend about 3 times in the past month the 15a efi fuse blows. The first time was the day after the timing chain was replaced I checked the ground for the efi by the manifold nothing checked all the obvious things nothing tryed another 15 that it promptly blew in half.
Called my friend and we started talking about what else ran off that fuse, yeah stupid o2 sensor so I disconnected it put a new fuse in reconnected it and bam truck starts right up. The two other times this has happened were while I was driving these times I did not have to disconnect reconnect o2 sensor just replacing the fuse was enough. Additionally visually the o2 sensor looks good not melted no broken wires In fact it appears to have never taken any extensive heat. Any ideas ?

 

so are you saying when the o2 sensor is disconected it doesnt blow?

 

No when I disconnected it and reconnected it it started and dident blow the fuse

 

My brothers truck was doing this too. It would randomly blow. He replaced the o2 sensor (which had 250k miles on it) and the wires were pretty worn down, and it hasn't happened since...like 6 months ago or so.

 

well it hasent blown again yet but i still cant find why it was.

 

Dont know if the affected it but I had realized after I got the truck back the shop had put my ignition timing back to 5 btdc where normaly the truck ran at 8 btdc. It has downey header and cut back flowmaster it always ran better advanced (actually a difference from 11-13 mpg and about 20-25 mpg) with 5.29s and worn ass 33 bfgs.
Well since I have returned it to where it was the efi fuse has stopped blowing and I got the pep back. Coincidence ??

 

Check the wiring from the alternator. Take off your air box and look at the wires under it and follow them to the place it meets on the inner fender, I had a fire the other day ! And it was a cross short from that! My whole harness is screwed!

 

hmmmI havent checked there yet and I dont want anything to catch on so Ill probly look at that tommrow when it gets light

 

Also it is not uncommon to have the EFI fuse blow from shorts in the O2 wiring due to it laying on the exhaust & burning thru....double check all the wiring.

 

x2 this is what blew my EFI fuse.

It sounds like you've checked the little pigtail that goes to the O2 sensor, it could be anywhere along that circuit - that wire goes in and out of all kinds of places!

 

Kinda late but..............I recently had a problem with my 15 amp EFI fuse blowing at random times on my 91' 3.0. I found that my O2 sensor wires were rubbing against my exhaust pipe near the manifold and rubbed a hole to where the wires were grounding out. If you changed your 02 sensor and now it runs, the 02 was probabally not the problem. I think you just moved the wires while changing the sensor and now it is not shorting out. I would fallow the wires from the sensor as far as you can and see if there are any exposed wires that may be rubbing and shorting.