I have an 1989 4 runner (22re) . My has been knocked out and is just a straight pipe. A friend who a toyota guy said this burns out the O2 sensor. Is this really true? What are the signs of a burned out o2 sensor? I have no "check engine" light. T

 

Well, is he talking about the absence of the converter affecting it or just because it has no back pressure? I havent heard of any O2 sensors going bad because of anything like that, only thing i would think would get burned is your valves if you dont fix your exhaust.

 

No, there is back pressure. I have a complete exhuast system with a muffler and a tail pipe after the empty catalytic converter. The O2 sensor is in the exhaust pipe right before the converter.

 

No, an open cat won't effect the upstream oxygen sensor.

If you're worried about it test it per the manual.

 

I'm having an issue related to an o2 sensor and lack of cat too. I bought this truck right after the cat. had been stolen. Then the PO had an exhaust shop just bypass (IE: only a muffler, no cat) and a new O2 sensor. Well, now with the O2 sensor in the truck runs very poorly and when it is unplugged the CEL is on and the ECU (presumably) defaults to a failsafe setting. I'm getting pretty bad gas mileage now and think it is related to this.

I do have the FSM and will check the O2 sensor for proper functionality, but the guy who installed the exhaust said to just leave the O2 sensor unplugged because the fact that there is no cat. will mess up the readings anyway (which doesn't make sense to me as the O2 sensor was upstream of the cat. to begin with).

Any thoughts/advice on this?

 

I have the same problem with 87 4runner, 22re. just replaced new 02 sensor due to rough idling. it fix the idle problem but it burns lots of gas. need help

 

I have an '89 truck with no cat and 22RE.

It's an interesting question, about whether no cat could burn out the O2, but I'm guessing it shouldn't have anything to do with that, as Co_94_PU says.

My truck just rolled over 236K miles. The kid I bought it from was a big junkyard parts fan. He had put a new manifold in it before I bought it, but (I assume) the downpipe where the O2 sensor attaches was original. I put a new exhaust on it about 10 months ago right after I got it, and had the cat left off.

Some time ago my CEL started blinking on and then off even as I drove down the road. I pulled codes and saw O2 sensor stuff. Friends told me that new O2 sensors tend to make vehicles run better and get better mileage even if the old one hasn't failed. So I figured I would just replace it. I got one and saw that the mounting bolts were completely rusted.

I took the truck to a guy hoping he'd be able to remove the hardware and install the new sensor. He found that the wires to the sensor had gotten too close to the exhaust and melted. He just fixed the wires and declared it fixed since the CEL would stay off.

Next long trip I took, after about 2 hours on the road the CEL came on and stayed on. During that trip I got amazingly sheety gas mileage. On one windy stretch of NM highway I got LESS THAN 14 MPG.

So I dug into my wallet again and got a new downpipe and sensor.

CEL was off, and the truck ran like gangbusters. But then on the second trip the light came on again!

So I crawled under there and un-taped the splices in my wiring. They were way sloppy. So I stripped the wires and spliced them really clean (I'm generally an idiot with vehicles, but have done phone and computer wiring, so I have some mad skillz in that area).

So all that was about 500 miles ago. The light is off. Mileage has gone from no better than 20 (usually high teens) to solid mid-20s even in the mountains and cold air.

To anyone who has issues with O2 sensors, I would urge you to look at the way the wires are routed to them. Obviously those wires have to be reasonably close to the exhaust (right over the cat if you have one) since that's where O2 sensors live. A couple clips go bad, a ham-fisted mechanic doesn't put the wire back into the clips... whatever. The wires don't have to move very far before they are close to the exhaust.

I fixed my splices. Actually shortened up the wiring because there was too much. Taped it all up with electrician's tape. Then I went to the parts store and got some heat shield tape and wrapped it up with that. Finally I rigged up a good, solid method for zip-tying that sucker up as close to the underside of the body and as far above the pipe as I could.

Will my new O2 sensor die prematurely because there's no cat downstream of it? If it does, you'll hear about it here first!

 

Straight pipe or no CAT does not affect the O2 sensor, Location does.
In later models with a after CAT O2 sensor the ECU will CEL with a bad or removed CAT, That's what its suppose to do is let you know the CAT is bad.


The O2 sensor is extremely important on EFI engines and must be working correctly to keep efficiency of the air/fuel and detect problems of the engine, Its not some EPA conspiracist idea to make you get bad performance and buy more gas.
The O2 sensor is very susseptible to damage by antifreeze coolent, It can weaken or render non op, As also the CAT.


For Toyotas is has been proven that the Denso O2 sensor is the only one that works correctly and that the Botch are insufficient.


As mentioned above check the harness to the O2 sensor for breaks and shorts, Most problems accure where the harness crosses over the exhaust pipe and where the harness comes loose from the passenger side engine compartment fender and brush up against the exhaust manifold or rubs against the bellhousing.


I am not going to even touch into the argument of back pressure, scavenging effect and the PAIR valve.

 

I've also been running with no cat on my '89 'Runner (5-speed, V6). I'm still using stock pipe diameters and muffler. I have yet to encounter a CEL due to no cat.

 

I ran my 22rec with a modified Cat for years no problem

I did notice these O2 sensors if they sit for a long time a few months will cause a the CEL to light .

Cleaning them on a wire wheel seems to cure the problem at least in my case I am talking about the older single wire ones.

 

I should clarify:

When my O2 sensor is plugged in I have NO CEL, but the engine runs terribly; rough to the point where I have to unplug to O2 sensor.

When the O2 sensor is unplugged I get a CEL (as one would expect) but the truck runs much more smoothly.

I still haven't had a free moment to test the O2 sensor and look over the wiring, but that is step 1 & 2. If that doesn't do it, step 3 is a new Denso O2 sensor (not sure what "new" O2 sensor the PO put in, so it may be something sub-standard). I'll post results when I finally get a chance to look at it.

 

I would definitely check the wiring, one day I noticed my mileage got really ˟˟˟˟ty, and it kept up, the truck seemed to be running fine, I was under the truck and notice the O2 harness looked burnt, so I rewired and rerouted that part of the harness away from the exhaust, replacing the O2 Signal wire solved all my problems.

Also make sure you run the O2 signal wire separetely from the rest of the harness, if you dont have shielded wire to replace it.

Running with no cat will absolutely NOT damage the O2 sensor. Have been doing it for many years. Also it is upstream of the catalytic converter. Unless you also have the one that is after the cat, well then, I dont know anything about that.

 

You're running open loop with the sensor unplugged, you should be running rich, smelling fuel in your exhaust etc. If it runs better this way you may be getting unmetered air in the mix which is balancing out the excessive fuel. Worth checking for cracks in the intake hose or other leaks.

Could be as simple as a really bad sensor which can't switch fast enough to give the CPU the correct mix numbers, as others have said. Check switching rate with an analog voltmeter before buying a new one though.