Please confirm my diagnosis of one bad O2 sensor

[Timbert]

Solved. Thanks to everyone for the help.

Finally got a second set of legitimate Bosch 13806 sensors from Rockauto and installed them after the cats. All four that I replaced (no-name sensors) were either shorted on the heater circuit or at more than 12 ohms (the Bosch ones were 2.5 to 2.8 out of the box and my Durametric report on the resistance with the four Bosch ones installed is right at spec). Plus, at least one had a shorted signal lead that threw lots of errors and Durametric showed a negative voltage rather than the proper swings of positive current. All four of the bad ones would generate voltage with the propane torch, but that's not good enough to keep the CEL off.

I now have proper voltage swings, and the idle fuel trims are .08 and .12 or so, so I may have a very small vacuum leak but not enough to cause a CEL.

So case closed, I hope, on the major issue of rough idle and bad sensors causing the CEL. Note this was a car I purchased recently as a known basket case, so normal troubleshooting procedures had to be modified. I didn't know what had been done to the car, but I learned right away the sensors and the MAF were suspect, and all non-Bosch, but I also had a major vacuum leak at the j-pipe that didn't show up with the smoke test. That's because I used the j-pipe connection to attach my ghetto smoke machine. Duh.

I also learned an easy-to-overlook fact that the heaters are on the same circuit. So an open circuit on one sensor, either front or rear, will also throw the code for its mate on the other side of the car. Like Christmas tree lights wired in series: when one bulb goes out they all turn off.

[flouese]

TIMBERT,

Care to share how you constructed your "ghetto" smoke machine.

[Timbert]

I Googled "smoke machine" or "vacuum leak" and did the one on Youtube using a one gallon paint can. Two 3/8 holes drilled in the lid, attached a couple air hose fittings that came with my compressor tools. One connects to the compressor, the other to a washing machine fresh water hose (smaller diameter than a garden hose). Jam the other end somewhere in the intake. Not the J pipe because that's a likely source of a vacuum leak. Do this all with the engine off, and cold, as warm engine parts can expand enough to close off the leak you're trying to find.

If I had to do it again, I would remove the MAF which you have to do any way to keep it from getting contaminated, and shove some rags in there to keep the pressure from coming back out the air filter. But I'd attach the smoke end of the hose to the manifold. My best idea is to use the rear-facing port on the top of the manifold behind the passenger (US) seat. It's the part that's used on the opposite manifold to connect to the brake booster.

Then put some mineral oil on some rags and light them, wait a few seconds and stomp out the flame. Drop the smoking rags in the can and hammer the lid closed. Tough to close completely if there's a lot of old paint on the lid but do your best. Have someone turn your compressor on for a few seconds at a time, or rig up an in-line valve, or use an electric tire inflator to generate some low but steady pressure, I think a couple PSI is enough. Fresh air being pumped in will keep the smoky rags going, but mine went out a few times. Then look for smoke coming out of the motor, and have a flashlight handy.

Apparently you can use the same thing to locate exhaust leaks.

You're looking for air that cheats its way in after the MAF, so maybe prop the throttle body open to make sure the smoke can get to the resonator and rest of the intake before the TB, maybe there's a leak there.

But don't take my word for it, I did all this and did not find the leak but may get back in there depending on how my fuel trims look later on.

[JFP in PA]

Originally Posted by Timbert

I Googled "smoke machine" or "vacuum leak" and did the one on Youtube using a one gallon paint can. Two 3/8 holes drilled in the lid, attached a couple air hose fittings that came with my compressor tools. One connects to the compressor, the other to a washing machine fresh water hose (smaller diameter than a garden hose). Jam the other end somewhere in the intake. Not the J pipe because that's a likely source of a vacuum leak. Do this all with the engine off, and cold, as warm engine parts can expand enough to close off the leak you're trying to find.

If I had to do it again, I would remove the MAF which you have to do any way to keep it from getting contaminated, and shove some rags in there to keep the pressure from coming back out the air filter. But I'd attach the smoke end of the hose to the manifold. My best idea is to use the rear-facing port on the top of the manifold behind the passenger (US) seat. It's the part that's used on the opposite manifold to connect to the brake booster.

Then put some mineral oil on some rags and light them, wait a few seconds and stomp out the flame. Drop the smoking rags in the can and hammer the lid closed. Tough to close completely if there's a lot of old paint on the lid but do your best. Have someone turn your compressor on for a few seconds at a time, or rig up an in-line valve, or use an electric tire inflator to generate some low but steady pressure, I think a couple PSI is enough. Fresh air being pumped in will keep the smoky rags going, but mine went out a few times. Then look for smoke coming out of the motor, and have a flashlight handy.

Apparently you can use the same thing to locate exhaust leaks.

You're looking for air that cheats its way in after the MAF, so maybe prop the throttle body open to make sure the smoke can get to the resonator and rest of the intake before the TB, maybe there's a leak there.

But don't take my word for it, I did all this and did not find the leak but may get back in there depending on how my fuel trims look later on.

I'll give you points for creativity on making your own smoke generator, but connecting it to your intake and expecting to see where it leaks out is not how these things work.

The generator produces smoke, which is emitted through a small wand that is run along vacuum connections while the engine idles. What you are looking for is for the smoke to suddenly disappear as the wand tip approaches the leak sources. I seriously doubt you can find a vacuum leak by flooding the intake system with smoke, expecting to leak out, unless the leak source is absolutely massive.