Front O2 sensor wire short to ground, then odd aftermath.

[dogtail]

Trying to figure out what got F'd up from my front Cali 02 sensor wire that broke off and shorted to the transmission. Not sure how its all related but here's what happened. Had a EFI 20 amp fuse blow from I think the front O2 sensor wire hitting ground, replaced fuse, then blew again and I found the wire and taped it off, replaced fuse hasn't blown since in like 400 miles, so thats all set. Having weird running issues now, like starving for fuel intermittently, can drive down highway fine, but after idling in parking lot for a bit, runs like super crap. New fuel pump, fuel filter, MAF, plugs, wires. I tried swapping out the coils from my parts rig, no change.
While it was running like crap, I swapped out the EFI relay, and then it ran great, so I thought I fixed it, then it came back next day. No idea whats going on.
I think the short may have damaged something in the circuit connecting to the front O2 sensor. Anybody have a diagram for that circuit, 99/5spd/3.4L? No idea whats going on.

 

[hamsandwiches]

If it shorted, the o2 sensor wire likely got very hot for a moment which could have increased the internal resistance of the wire and transmit unusual signals to the ECM. Is it currently throwing o2 codes?

I would bet the sensor is ruined or at least the wires are.

 

[dogtail]

That O2 sensor not even currently hooked up, so yeah related codes.....Issue not coming from the lack of a sensor hook up either, its intermittently running really really really bad, like starving for fuel. I can drive thousands of miles without an O2 sensor just fine. Had a few 3rd gens so I know how those issues. I have to run a new section of O2 harness for sure, there is no more connecting plug. Right now I have it isolated and taped off. Trying to fix this while I'm working 12+ hr days 7 days a week not helping. Would like the related circuit diagram who ever has one.
I replaced the fuel pump (Denso), wondering if that's the issue, its acting like its running out of fuel. Seems like running lower RPM parked for extended times triggers issue. While driving highway it runs fine.
I have parts vehicle at the house to pick from, just tried fuel relay, no change.
I'll try ECU I guess, I'm poking and hoping replacing and ruling things out at this point.

 

[Bad Luck]

That O2 sensor not even currently hooked up, so yeah related codes.....Issue not coming from the lack of a sensor hook up either, its intermittently running really really really bad, like starving for fuel. I can drive thousands of miles without an O2 sensor just fine. Had a few 3rd gens so I know how those issues. I have to run a new section of O2 harness for sure, there is no more connecting plug. Right now I have it isolated and taped off. Trying to fix this while I'm working 12+ hr days 7 days a week not helping. Would like the related circuit diagram who ever has one.
I replaced the fuel pump (Denso), wondering if that's the issue, its acting like its running out of fuel. Seems like running lower RPM parked for extended times triggers issue. While driving highway it runs fine.
I have parts vehicle at the house to pick from, just tried fuel relay, no change.
I'll try ECU I guess, I'm poking and hoping replacing and ruling things out at this point.

The front oxygen sensor controls/monitors the air/fuel mixture. I'd start with replacing that first since you know it's not functioning properly.

 

[dogtail]

The front oxygen sensor controls/monitors the air/fuel mixture. I'd start with replacing that first since you know it's not functioning properly.

I'm gonna replace a large section of that harness cause it got damaged, it looks as it runs over to the battery area. The issue is something different cause it won't run like that with the O2 unplugged, but I think it was triggered by the short to ground.

 

[Bad Luck]

I'm gonna replace a large section of that harness cause it got damaged, it looks as it runs over to the battery area. The issue is something different cause it won't run like that with the O2 unplugged, but I think it was triggered by the short to ground.

You don't think something that adjusts the amount of fuel injected into the cylinder could cause a rough running condition?

 

[JohnMc]

I'd suggest getting an OBD2 scanner (they sell cheap ones that work with a phone) and see what the engine is doing.

The front O2 sensor is a fairly important sensor in the grand scheme of things. With it malfunctioning (probably worse case) the ECU gets sent on wild goose chases trying to correct the mixture. With it unplugged the ECU just has to revert to open loop running, no ability to sense fuel mixture problems and try to correct them

 

[hewitt-tech]

I'm gonna replace a large section of that harness cause it got damaged, it looks as it runs over to the battery area. The issue is something different cause it won't run like that with the O2 unplugged, but I think it was triggered by the short to ground.

:brick:
Your engine WILL NOT run correctly without proper signals from the upstream 02 sensors and will do exactly what you are describing.

This is what I call the gas cap syndrome. It is where people ignore the most obvious problem and instead search for another reason for the problem. I call it the gas cap syndrome because a lot of people will have trouble codes for something completely unrelated to the EVAP system and will blindly take the advice of someone online who recommends replacing the gas cap like that will somehow magically cure a CEL for something like an engine sensor.

You need to repair the obvious damage to the wiring first, replace the Heated 02 Sensor(aka A/F sensors) and plug them back in. Your 02 sensor is likely shot as well. The wire damage could have caused the damage to the sensor or the shorted sensor could have damaged the wiring, fix/replace both. It is also fairly common for one sensor to go out and take the other with it. In the case of a v6 or v8 engine they should also be replaced as a pair since this will keep your bank 1 and bank2 fuel trims as close as possible to each other. Think about it like a carburetor tune up but for your fuel injection.

 

[dogtail]

You don't think something that adjusts the amount of fuel injected into the cylinder could cause a rough running condition?

I'd suggest getting an OBD2 scanner (they sell cheap ones that work with a phone) and see what the engine is doing.

The front O2 sensor is a fairly important sensor in the grand scheme of things. With it malfunctioning (probably worse case) the ECU gets sent on wild goose chases trying to correct the mixture. With it unplugged the ECU just has to revert to open loop running, no ability to sense fuel mixture problems and try to correct them

Yes I have a scanner. I had the front O2 sensor disconnected for 3 months without this issue, cause need to replace harness, plug got wrecked on a cat breaking in half. So after the fact, plug looked innocent enough sitting there and didn't look like it would hit anything or short til I got time to replace. Time went too long, for some reason the remainder of the plug came off and that made the wires bare and hit the transmission and shorted. I know its my fault and I need a face palm with a cactus. But here I am.
Overworked with very little sleep and havn't had time to fix. Now I just have to get the time to do everything right, instead of working on it 30 minutes here, and an hour there. Its been a my DD so it never stops, til now 360K+, so if ran with a little hiccup and would drive, no issue if it got me on my way. But time to get serious, and give it some attention.

 

[TheDurk]

Trying to figure out what got F'd up from my front Cali 02 sensor wire that broke off and shorted to the transmission. Not sure how its all related but here's what happened. Had a EFI 20 amp fuse blow from I think the front O2 sensor wire hitting ground, replaced fuse, then blew again and I found the wire and taped it off, replaced fuse hasn't blown since in like 400 miles, so thats all set. Having weird running issues now, like starving for fuel intermittently, can drive down highway fine, but after idling in parking lot for a bit, runs like super crap. New fuel pump, fuel filter, MAF, plugs, wires. I tried swapping out the coils from my parts rig, no change.
While it was running like crap, I swapped out the EFI relay, and then it ran great, so I thought I fixed it, then it came back next day. No idea whats going on.
I think the short may have damaged something in the circuit connecting to the front O2 sensor. Anybody have a diagram for that circuit, 99/5spd/3.4L? No idea whats going on.

Here is the engine control EWD for 2000 V6. I have the '99 on paper as that is my year and it is the same.

I agree with the rest. Get the sensor fixed so that you are running in closed loop before you go chasing anything else.

 

[dogtail]

Here is the engine control EWD for 2000 V6. I have the '99 on paper as that is my year and it is the same.

I agree with the rest. Get the sensor fixed so that you are running in closed loop before you go chasing anything else.

Thanks, much appreciate the diagrams, that's what I wanted. I'll just have spend the time to tear into it and get it done.

 

[Myjar89]

My issues

I have an 01 limited. These sound about like my issues. Running ridiculous. I have replaced-plugs,wires, coil, tps, cleaned throttle body. My O2 is also unplugged, has been for a long time. 4Runner ran great for two days after coil replacement. Then terrible again. Ran great after the plug/wire. Next day, back to terrible. I also am wondering if there is something electronic. I had a small fire underneath, near transmission pan. and I’m afraid it burned something up. Not sure what to do next.

 

[dogtail]

I have an 01 limited. These sound about like my issues. Running ridiculous. I have replaced-plugs,wires, coil, tps, cleaned throttle body. My O2 is also unplugged, has been for a long time. 4Runner ran great for two days after coil replacement. Then terrible again. Ran great after the plug/wire. Next day, back to terrible. I also am wondering if there is something electronic. I had a small fire underneath, near transmission pan. and I’m afraid it burned something up. Not sure what to do next.

I meant to followup on this thread but forgot. Mine is all fixed, I spent a day just going thru everything. I have well over 1,000 miles on it since fix, so I know its 100% solved. It runs very good now and hasn't blown a code.
Here's what I did. I replaced the section of harness at the front O2 sensor, essentially I just soldered/shrink tubed a new plug on that was missing. I scalped it from my parts rig. I replaced the front temporary old cat I swapped out after new one broke in half (I had new one sitting in my garage for a while I got on a warranty replacement on one that broke in half, just never found the time to replace). I installed two new Denso O2 sensors. I loosed up all exhaust bolts and tightened it back up again. Reason I did this is I think my previous cat that broke had to much strain on it when I replaced it, so by loosening the whole exhaust and tightening it together and make sure no exhaust stress. So after this it ran pretty good, idle was a tad rough, and threw a code for the TPS, so I scalped one from my parts rig. Then all has been great since then.
So what I think happened, is something happened to my rear O2 sensor, that was really messing with the ECM. It was intermittent at 1st, then it went full death spin. Cause I know my harness did short to ground and its was in the O2 loop, and had been running a while fine without the front O2 sensor even hooked up, I think like 3 months. My temporary cat wasn't clogged. Everything points to rear O2 sensor, something in it fried from the short.
Moral of my story is - I was pushing it by not attending to maintenance I knew I had to do. My longtime loose free willy O2 plug somehow came off and wires hit the transmission, based upon an ignored repair I needed to do. My heavy 7 day work schedule is valid, but I should have been more attentive. This I use for a DD and do over 1,000 miles per week in it fully loaded with heavy gear. The thing is a work horse, it never lets me down, unless I let it down.