[triumph4062]

Hi to all the Corolla experts!!

I have a very reliable '97 Corolla, it's not pretty but it gets me arround! It has 270k miles, and burns some oil. It failed the smog for the 1st time. I've attached the results.

My question is can a bad cat make it fail at 15mph, but pass the 25mph test? At the smog station it was smoking noticeably at 15mph but not 25mph.

My assumption is due to the age of the cat (it's the original cat afaik) and due to the burning of oil it's toast. Could it be something else?

I like the car, it's been good to us (as have all our toyotas) it's $250 at the muffler shop for a weld in cat, which for 2 years piece of mind is ok, plus it's chaeper than another car at the moment.

I've attached the results for information.

Thanks in advance for any help anybody can give, it will be much appreciated!

 

[Pete Suhman]

I recommend going to a shop or the exhaust shop, and having them remove the nuts and bolts which retain the cat, and then having them install new ones - just new nuts and bolts.

Then if you want to replace your cat, you can buy a new one cheap, and put it on yourself. Plus you can sell your old one, and recoup maybe half the price of the new one! It's held on by only four bolts.

If you do this, be sure that your new one is a "flange-mounted" unit, rather than one which slips onto the pipe and gets held by regular exhaust clamps.

Then you're only looking at $25 or whatever for the bolt job, and whatever the new cat costs.

 

[triumph4062]

Pete,

The cat on my car is integral with the exhaust,(see edit!) the new cat if I get one will be $250 from the muffler shop. The cheapest I can get one on line is approx $200 for a CARB approved cat. There's probably cheaper ones to be had I guess.
Thanks for the reply

I stand corrected, the cat is a bolt in unit, I was looking further downstream. I'll put it on jack stands and see if I can break the bolts loose before I go to a muffler shop.

 

[cb91710]

You're still high on the 25mph.

Try it again, but this time, do for a good 50 mile drive to get the cat nice and hot and the engine up to full operating temperature.
I had a '91 Escort that failed in '96 after driving about 10 miles to the test station... passed with no problem after driving another 20 miles.

 

[triumph4062]

You're still high on the 25mph.

Try it again, but this time, do for a good 50 mile drive to get the cat nice and hot and the engine up to full operating temperature.
I had a '91 Escort that failed in '96 after driving about 10 miles to the test station... passed with no problem after driving another 20 miles.

The car was good and hot when I got to the smog station, after a 40 mile commute.
The routine with the smog guy is he'll ask how far you've driven, if he doesn't like the answer he'll tell you to drive on the freeway for 30 minutes, then come back.

I'm not sure the 15mph HC is due to the cat not being adequately warm, more likely the cat's bad or something else is bad, which is why I was asking.

 

[DannoXYZ]

The CO2 and O2 numbers actually show that your cat is working perfectly fine. The air-fuel mixture is just too rich with excess fuel for the cat to combust excess HC (note no free O2, it's all been used to burn up HC).

I'd verify vacuum at FPR and pressure in fuel-rail. If you don't want to do that, just replace the FPR and upstream O2-sensor and it should pass easily.

 

[triumph4062]

Danno,

I guess the 0.0% O2 is a giveaway! It would make sense as it was smoking black smoke (not much but it was there) on the dyno at 15mph.

I'll test the FPR today and see if it's getting vacuum. I would assume the O2 sensor is ok otherwise I'd be getting a check engine light, on the other hand a replacement is $20 so might as well replace it.

Thanks for the reply!

 

[DannoXYZ]

O2-sensor fault takes a while to trigger. I had my downstream sensor disconnected for two-three weeks before the light came on.

To test for O2-sensor fault:

1. Pull EFI to reset ECU
2. Short TE2 and E1 on DLC1 port
3. Start car and warm up with all ACC off
4. Let idle for 3 minutes after warm-up
5. With AC ON, accelerate to top-gear using 1300-1700rpm, centered around 1500rpms, don't let revs fall below 1200rpms on shifts
6. Maintain speed between 40-50mph for 1-2 min after starting acceleration
7. If malfunction exists, CEL will illuminate within 60-seconds.

As you can see, it's quite difficult to light the CEL for bad O2 sensor. It could be partially working and throwing off fuel-mixtures enough to fail an emissions test well before triggering CEL.

At idle, vacuum at FPR should be 20-22 in.Hg.

Also measure resistance of ECT - engine coolant temp-sensor. Cold engine should be around 2.5K-ohms. Warmed up should be 0.15-0.25K-ohms. If ECT is defective or sending out erroneous data, the ECU will be fooled into thinking engine is cold and will enable cold-start enrichment. Which is in the 10.0:1 AFR and will definitely be too rich to pass smog check.

Good luck.

 

[triumph4062]

O2-sensor fault takes a while to trigger. I had my downstream sensor disconnected for two-three weeks before the light came on.

To test for O2-sensor fault:

1. Pull EFI to reset ECU
2. Short TE2 and E1 on DLC1 port
3. Start car and warm up with all ACC off
4. Let idle for 3 minutes after warm-up
5. With AC ON, accelerate to top-gear using 1300-1700rpm, centered around 1500rpms, don't let revs fall below 1200rpms on shifts
6. Maintain speed between 40-50mph for 1-2 min after starting acceleration
7. If malfunction exists, CEL will illuminate within 60-seconds.

As you can see, it's quite difficult to light the CEL for bad O2 sensor. It could be partially working and throwing off fuel-mixtures enough to fail an emissions test well before triggering CEL.

At idle, vacuum at FPR should be 20-22 in.Hg.

Also measure resistance of ECT - engine coolant temp-sensor. Cold engine should be around 2.5K-ohms. Warmed up should be 0.15-0.25K-ohms. If ECT is defective or sending put erroneous data, the ECU will be fooled into thinking engine is cold and will enable cold-start enrichment. Which is in the 10.0:1 AFR and will definitely be too rich to pass smog check.

Good luck.

Danno,
Thanks for that info. I don't have a tacho on the car so probably can't accurately gage engine rpm, I'll probably just change the O2 sensor, I'm off to borrow a friends vacuum gage to check the vacuum, thanks for the help!
Dave

 

[triumph4062]

It failed again! The 15mph HC is now 120.

The O2 sensor did help, at idle you can tell it's running rich from the smell of the exhaust. With a new O2 sensor that richness went away.

Standing behind the car at the start of the 15mph portion of the test it was smoking white smoke quite badly for about 5 seconds before it slowly went away (another 5secs or so), I'm assuming it's burning oil quite badly, not sure why it goes away and isnt continuous. If it averages the 15mph HC over the time period of the test I can see why it probably failed.

It probably didn't help that the smog guy left the car idling while dealing with some other customers.

 

[DannoXYZ]

Hmmm, burning oil won't cause emissions issues. Though, you technically can fail if they see any smoke. Fueling issues may have multiple sources. If you want to replace, then do all of the following:

- FPR
- injectors
- fuel-filter
- MAP-sensor
- ECT-sensor
- IAT-sensor

Any one of these can contribute to rich mixtures. Also wouldn't hurt to do piston-soak and run a bottle of Redline SI-1 through a tank of gas.

 

[H-Man]

Autozone will loan you a fuel pressure tester. You need a $150 deposit but unless it is missing parts it will be able to hook up at the fuel filter banjo.

 

[DannoXYZ]

Yeah, I suspect fuel-pressure too. Might be too high at the lower-load range. Sign of FPR or vacuum-leak problem.

 

[triumph4062]

The Corolla passed with a new CAT.

The HC at 15/25mph was 23/7 ppm down from 142/40ppm.

The NO went from 198/268ppm to 0/1ppm.

That car also accelerates a lot better as well.

Another 2 years before we have to go thru this drama again!

 

[DannoXYZ]

Good job fixing this!!!

Please post smog results to compare with before. Your car is Federal model with one big bolt-on cat? Or a CA model with two cat with a small secondary one? Thx

 

[H-Man]

I'd still check fuel pressure. I don't like the look of those NO numbers, it looks almost like the the precat is getting enough oxygen to clean up the HC by cracking the NO.