93 4Runner EFI Blowing when shifting to reverse???
 

Just looking for pointers. My son was going to drive my 4Runner to work the other day. And he backed out of the driveway and once he was in the street he stalled.........He moved the truck to the side of the road by pushing it. And it would not turn over.

Did some research everyone was saying if EFI fuse if blowing could be the O2 sensor wires burned out on the exhaust.......or the fuel pump is bad. Had a mechanic friend come over and after dropping $150 for a new Fuel Pump we dropped the tank and put in the new one. We had rolled the truck in reverse into the my drive way so once we had it all buttoned up they followed me to the gas station and I put some fuel in it and the drove home......I parked front end in, which means in the morning I'd have to put it in reverse to get out. I wake up to go off to work fired up the 4Runner with no issues and went to back up and "POP" goes the 15 amp EFI fuse.

I had to get to work so I went.

Got back home today and unplugged the O2 sensor as that was the next in line to see if that was the culprit........put in a new 15 amp fuse and I let it warm up.......pulled forward and it was idling. I was going to take it for a spin.....put it in reverse and "POP". Put in another fuse put it in reverse and "POP".

I did replace the reverse switch in the side of the trans that signals the revers lights to turn on a few months back.

To me this is just strange that the reverse light electric system is popping the EFI. Also, the back up lights are not turning on.

BTW, I tested the EFI relay and that is in tip top.....did the battery with voltmeter test......and it's a-okay.

Any thoughts?

93, 4 Runner, 4x4, V6, Manual Transmission

You have a short on your wiring to back-up switch OR your back-up lights. Pls see my signature

Toyota engineers had the bad practice of taking power from fuses named after the wrong systems. For example on the 22RE, power window, neutral safety sw, O/D indicator, back-up light sw, and alternator excitation ( nothing to do with the engine at all.) take power from ENGINE fuse- DUH!
I'm pretty sure your back-up switch/light system also takes power from wrongly-named fuse.

Nice I'll start there tomorrow. Crazy that the reverse light line would be hooked up to the EFI.

2nd what Ray said!!

If this was your issue how might you go about finding the short?

If you have trailer lights start there, they may have used tape which fell off.

Visually inspect, the rear corners where the harness exits the cabin, along the trans.

If you can not find anything visually use a voltmeter set for resistance (ohms scale), fuse out engine off wheel chocks in place, measure at the fuse, switch, and both lights. The power wire will show the least resistance to body ground nearest to the short.

Hmmm. Yes, this could be a clue.

It shouldn't be. I show the reverse switch powered by Gauge and Cig.
https://cimg1.ibsrv.net/gimg/www.yot...1dc9f73ddb.png

Good advice (as usual).. But it seems more likely something happened with your switch replacement. Like tangling up the transmission harness with the O2 sensor wire.

I'm not surprised with Toyota... See scope's post above? Gauge AND CIGarette fuses power the back-up light system.

Anyway, it's most likely a short on the wiring.

Yup. Mine blows the gauge fuse when I put it in reverse. I've been mostly lazy trying to find the issue, so I just unplugged the wire from the tranny. Bad fix but it works.

I have unplugged the wire from the transmission and there is no issue as it is out of the equation (like 128keaton did).......but this is my wife's vehicle and I need her to have those back up lights.

At this point I am getting the truck ready for smog......and we are in SoCal.....so for the time being I am going to leave it unplugged. Once we pass smog and get past that I will start in on the wiring issue.......I also need to replace the switch to the back window in the center console and get that damn thing going again.

I did however go under to investigate........and I've never done any real electrical (save for installing a stereo or two) on a vehicle before so I am a bit intimidated at taking everything apart to trace two wires and re-run them with fresh wires.

Any advice on the job?

Locate the problem before doing anything !!

Cutting and hacking the wiring harness just makes a big mess !!

You DO have a multimeter, don't you? If not, do that first, figure out how to use volts and ohms (continuity).
https://www.harborfreight.com/7-func...ter-90899.html

I have ground continuity on both sides of the backup switch wire........so would it be safe to say that there is a sleeve worn on either of those wires? Everything is tucked in really well and covered with a plastic sheath. So I am assuming that I am to start undoing all of that and replace the wires.......?

do both wires show a similar resistance, this indicates they cut through in the same place. "It is tucked in really well", yep sort of the problem in a nut shell.

You want to follow that loom visually, inspect every place it contacts metal, sharp bits, or hot bits. Since it is fully loomed it should be easy to find the damage, its a lot harder on bare wires without loom because it only takes a pinhole.

If you have power windows, you should have a back-up light relay, and on the R-W wire out of the switch you should get measurable resistance to ground; at least 25 ohms. All that is there is the coil of the relay. So "zero" ohms to ground should be a short.

But the B-O wire goes to a fuse, then the ignition switch! You should get infinite ohms there! That, coupled with your blowing the EFI fuse rather than one that has something to do with the back-up circuit, tells me something got REALLY screwed up. Almost certainly when you replaced the switch.

Check your wire colors to start. If not R-W and B-O, you're real close. If you have the right colors, pull the backup relay and re-check R-W. If still zero ohms, you have a short in that direction.

Pull your EFI fuse and check for continuity from the fuse to the switch. If they're connected, that's clearly not right.

Your problem is not inside the harness; you DID something when you replaced the switch. Maybe as simple as getting a wire caught in the shifter linkage. It should be visible.