Think I need a new CAT

[Hugh R]

Failed NOX badly, engine was plenty hot, and it barely passed two years ago. No changes to the car since then.

[porwolf]

Sorry to see that, Hugh. Seems like the allowable NO levels for your '84 are far below the ones for my '79SC. That one passed easily less than a year ago:

[slodave]

Did you smog with the SW chip in place? If so, that could have done it. The cat is old and the numbers would be high, but the chip would have put it over. I put the stock chip in before the test.

[Targa Me]

Hugh, let us know the results after the new CAT.
With high NOX numbers, I was thinking you might need the fuel injectors rebuilt or maybe your air intake has a breach, getting extra air intake somewhere.

[Hugh R]

Tested and passed for years with the SW Chip.

[slodave]

Hugh, that may be, but the cat is getting older with use and the chip is not helping.

[Lapkritis]

I'm not sure I would peg this as a cat issue. You have room on the Hydrocarbons and carbon monoxide. I've attained pass after receiving these results by simply adding fuel. If you have a SW chip then that might do it. As another has mentioned, if you have a vacuum leak, even very small, this could do it.

Do you have a wideband O2 sensor to monitor? I ran datalogging on my system during the emissions test to confirm the tune was off. I would suggest you do the same as part of a scientific approach. Throwing parts at the problem starting with the most expensive first is not my recommendation.

[Hugh R]

Right or wrong, I ordered a new CAT from PP. Couldn't find any vacuum leaks. TRE had it a month or two ago for a different issue and said I was good with fuel pressure, electronic pulse, spark, etc. Passed SMOG for several tests with the SW chip in the past. Steve told me it would pass, all things equal. Shown a flashlight through the old one and couldn't see anything. With the new one I can see light.



Looks like the old CAT may not have been stock, don't know. I'll put it in this weekend and we'll see. About $530.

The nice thing about living in CA is the old one came right out, no frozen bolts. Out in about 20 minutes. Plus jacking it up and removing the L/R tire.

[Hugh R]

Well the new CAT didn't do the trick, my NOx almost tripled!!

The test guy seems knowledgeable. He said try a new O2 sensor, should have done that in the first place. He says the new CAT has less restriction and with a bad O2 sensor its leaning out the fuel:air mixture big time.

Any thoughts, other than I'm an idiot and just may have wasted over $500 on a CAT that I didn't need?



Checked out wide band O2 sensors, can one particular one just plug and play?

Thanks Guys.

[DRACO A5OG]

PMed you,

Jim

[Targa Me]

Hello Hugh.
Here are my suggestions:
1. Replace the O2 sensor.
2. Keep the new CAT on the car.
3. Check your spark plugs. If they look like your running lean (and I'm guessing they do) have the injectors rebuilt.
4. Before you go back for a smog test for credit, have your mechanic test the car for smog unofficially, then go from there.
I'm curious, when TRE checked for vacuum leaks, how was that performed? I would suggest a smoke test.

Please keep us informed on your progress, the knowledge you gain will help others here.

[Lapkritis]

At this point the problem is getting more pronounced. Something is failing - a wideband O2 is useful so you can see results as you tweak and repair.

Given the huge increase in HC's and very low measurements HC's, CO and CO2 you are extremely lean on mixture. This could be due to a number of causes:

1) Fuel pressure regulator
2) Fuel filter
3) Fuel pump
- Test is to drive and monitor fuel pressure. An idle or rev test of the pressure won't tell you much of anything useful.
4) O2 sensor worn out (if this hasn't been replaced in awhile then it might be the cause)

5) Intake tract leak between MAF sensor and intake valve. This could be a loose clamp, blown gasket, torn plastic etc... more involved to diagnose if it isn't something obvious and you have to remove the intake system to investigate.

The challenge with these situations is the solution could be a combination of things; ie, It might take more than one silver bullet.

[scarceller]

Most likely you are running lean. You need to get a WBO2 reading to know exactly what AFR it's at at idle.

Also, if you have a hand held infrared temp gauge take a reading of all exhaust ports to see if any are significantly hotter than others. The hot ones are result of lean mixtures.

[scarceller]

One more thought. Take a voltage reading at the O2 sensor signal line with it connected. If it reads above 0.7vdc and never comes down then introduce a air leak by simply removing the Oil Filler cap, if it still stays at >.7vdc the sensor is most likely bad.

The sensors often fail and signal a false rich condition (>.7vdc) to the DME and the DME then leans the mixture because it has a false rich signal from the O2 sensor.

Often cars with bad O2 sensors run and idle significantly better when you unplug the O2 sensor.

[Flat Six]

An additional suggestion, Hugh -- when it comes time to re-test you might want to reconnect the brown jumper wires to pin 10 of the DME for added margin.

Good luck

[Hugh R]

Thanks guys, I'll try the voltage change thing and I can get an IR temp gauge.

DRACO A5OG (Jim) has kindly offered to bring some test instruments up and give me a hand. I'm not panicked about it, and I'll be out of town until the 2nd week of October, but I do want to get it resolved.

My air and fuel filters, plugs and Disto Cap and rotor have about 35K miles on them, and the plug wires look original. Thinking about replacing them anyway.

[Quicksilver]

Not sure what an SW chip does to the CA ground wire but that should be connected during smog specifically to reduce NOx.

A nice additional test is to get a an infrared thermometer gun. Put the car up on stands and start it up and see if the exhaust ports heat up evenly. It they don't you have a cylinder specific issue: spark, injector, or intake manifold leak.

[stlrj]

I just went through the same problem recently on my 87 3.2. It failed with high NOx too. All the rest of the numbers were good except for the fact they seemed a bit lean like yours. So, the following day I pulled the air flow meter and adjusted the spring tension down a few clicks and moved the pointer up a smidgen, took it in for a pretest at another smog shop where it passed. Later, I took it back to the same place where it failed and it passed.




Cheers,

Joe

[Hugh R]

DRACO (Jim) is going to pay a doctor's visit in a few weeks when I get back in town. Via' a few PMs I asked him about buying plug wire, plugs, O2 sensor, etc. He said, stop spending money until I at least look at it and run some tests. I love this Board!!!

[craigyirush]

Originally Posted by stlrj

I just went through the same problem recently on my 87 3.2. It failed with high NOx too. All the rest of the numbers were good except for the fact they seemed a bit lean like yours. So, the following day I pulled the air flow meter and adjusted the spring tension down a few clicks and moved the pointer up a smidgen, took it in for a pretest at another smog shop where it passed. Later, I took it back to the same place where it failed and it passed.




Cheers,

Joe

Aasse in Fullerton had to do the same thing on my 3.2 to get it to pass.