Failed smog but this is confusing...

[vssjim]

I am going to say different as a low O2 reading is either a dead sensors or a lean engine,as a high reading O2 is rich. Co does no show a rich engine on your test and NOx low does mean egr is functioning or late ignition timing, yes I know it is non adjustable. Try to get engine hot and spray some carb cleaner in air intake while using a volt meter in diagnostic plug socket for either side O2 sensor. under cap on daig connector is a legend to let you know which socket to hook up to. I they go high under rich condition O2 are fine. look at maf dirty low injector fuel spray etc. Most vacume leaks on a MAF car show up at idle and are covered at load or speed condtion. You can also check MAF and O2 but wide open throttle while checking O2's as at wide open they should stay above .8 as engine is in open loop and is rich for accelleration. This will also show good fuel delivery.

 

[EricF]

I don't believe your cats are bad, however, given the miles you have, you have to expect something to go wrong.
If the cats were going bad, I believe you'd be much higher than you are now.
You've done the tune-up, the timing should be checked to make sure it's where it's supposed to be.
Although it's 1991, I would see if there are any codes in the computer anyway, i believe you can check them by shorting the diagnostic connector with a paperclip.

running higher octane fuel won't help HC.
Fresh oil and a clean air filter will help unless they're good to go as well.
If your o2 sensor is old, I'd replace it, it's a non-heated version, they're good for minimum 30k, sometimes more.. the car computer would usually catch it if it goes bad, but if it goes "lazy", it'll probably get missed.

It wouldn't hurt to put a bottle of Redline SI-1 or Techron in the tank and run it for 80 miles at least.

 

[spasm3]

If you just want to pass, i would run the tank down and get some e-85. Add enough e-85 so that you have about 75% gas 25% e-85 Don't put in a lot,just enough to get through the test. then fill up with regular fuel after.

 

[nthach]

Well, my smog guy ran some diagnostics on the dyno and the cats are shot - they're reducing NOx but not really reducing HC. Other than that the engine seems to be running fine. I got 2 new Walker CARB cats on the way, I'll leave the stock post cat untouched.

 

[Olas]

With a correctly tuned engine, a CAT isn't necessary.

Fix timing, igntion, vacuum leaks, oil control, fuelling and any feedback devices, and it will pass an emissions test without a cat.

high HC could indicate a misfire, or a vac leak confusing an o2 sensor.. Are they doing 2/3/4/5 gas analysis?

 

[Scott_Tucker]

This engine is NOT running rich. It is barely failing. Combustion efficiency is good. At 280k it is likely your cat is weak, or even the O2 sensor could be causing this. A new cat will definitely clean it up. However, I would replace the O2 sensors first. It might net you slightly better mileage.

 

[Merkava_4]

Originally Posted By: nthach
I recall driving back home when suddenly I lost power due to a failed coil wire - I was running on 4 cylinders and dumping raw fuel into the cats for 5 miles.


That's it right there - your catalytic converter is toast. When that check engine light starts FLASHING, that means you have a severe misfire and you're endanger of ruining the catalytic converter. You're supposed to pull over immediately and call a tow truck.

 

[Olas]

Replacing the CAT might get the numbers down far enough to pass the test, but that is only treating the symptom, not the cause. If it were my own car I'd find out the cause of the high numbers and address the problem so the symtpom disappears.

With a failed plug wire and CEL, whats the betting that other systems aren't in tip-top shape, and could do with a spruce-up to restore efficiency and reduce emissions? When was the last time you cleaneed & gapped plugs? tested coilpacks? checked cam & ignition timing? injector spray test?
There are too many variables to consider without seeing a printout from the gas analysis

 

[nthach]

Originally Posted By: Merkava_4
Originally Posted By: nthach
I recall driving back home when suddenly I lost power due to a failed coil wire - I was running on 4 cylinders and dumping raw fuel into the cats for 5 miles.


That's it right there - your catalytic converter is toast. When that check engine light starts FLASHING, that means you have a severe misfire and you're endanger of ruining the catalytic converter. You're supposed to pull over immediately and call a tow truck.

But the confusing part was the the ECU didn't detect the misfire(Toyota ignition systems send an IGF signal from the igniter to the ECU, telling it an ignition event has happened), the coil still fired, but the burned coil wire kept current from reaching the distributor for one cylinder bank.

I replaced the main O2 sensors and I'm seeing an increase in MPG.

 

[steve20]

Originally Posted By: Olas
Replacing the CAT might get the numbers down far enough to pass the test, but that is only treating the symptom, not the cause. If it were my own car I'd find out the cause of the high numbers and address the problem so the symtpom disappears.

With a failed plug wire and CEL, whats the betting that other systems aren't in tip-top shape, and could do with a spruce-up to restore efficiency and reduce emissions? When was the last time you cleaneed & gapped plugs? tested coilpacks? checked cam & ignition timing? injector spray test?
There are too many variables to consider without seeing a printout from the gas analysis


It is advised to ready the bloody post, and previous responses before replying---so that one does not appear like they just landed from outer space