New Here with Questions

[modian]

I have (it's my wife's) a 1997 Avalon with 173K miles. It just failed a smog test with excessive NOx levels. The CO and HC levels were just fine, as I have recently replaced all three O2 sensors (brought on my a P0135 MIL code) and the plugs/wires were replaced one year ago. The smog guy said it was most likely an EGR problem since all the other gases measured real good on the test.

So I've done a lot of reading here to see how EGR affects emissions and what is involved in fixing the EGR problem. Since I don't have any EGR related MIL codes (actually, no codes at all) present I am wondering if the problem could be related to a blocked flow instead of a vacuum or electrical failure of some sort that would trip a code. Also, how big of a pain is it to get to all the parts to R&R them?

We have owned this car since 62K miles and outside of filter and fluid changes (oil, trans, coolant) nothing has been done engine-wise except for the O2 sensors and ignition parts I have mentioned. OK, I had the timing belt replaced and a new water pump and ancillary seals put on along with it. It made sense to do all that while the front of the engine was stripped.

Also, unrelated to this question: my valve covers are (and have been for some time) leaking. The dealer told me I should have the valves adjusted while replacing the gaskets. I'm a little confused about this, as I presume this engine has hydraulic lifters, and if so, there shouldn't be anything to adjust. Why am I being told to adjust the valves?

Thanks. My user name should be "modain", not my fat-fingered entry "modian".

[toyomoho]

This engine is a 1MZ-FE, the same as Camry with V6 option as such might review the Camry forum on EGR issues. The group has a wider audience.

Was this a engine RPM low and high test, what were the smog readings? The EGR is off at engine idle and light engine loads.

The EGR system has an exhaust temperature sensor that in part operates the system. The temperature is monitored by the ECU, there is a specific trouble code if the exhaust temp is too low.

Not up on access. You should be able see the EGR valve system on the intake manifold, the gases come from the rear exhaust manifold.

Suggest if you attempt to clean the system to pickup a Haynes manual on this car. The system is not too complicated but having a manual you can test various parts will still on the engine.

The engine uses shims to adjusts the valves, in most cases the valves never need adjustment. Is the valve train making noise? What is the dealer asking for this job $$.

The only concern with the valve gap is one that is way too small and might burn a valve and not readjusting everything. But this is very uncommon on these engines.

[modian]

Thanks so far for the help. The valves don't make any noise. So I guess I won't worry about them.

Here are the smog inspection measurements:

.......|RPM |%CO2|%O2 | HC (PPM)| CO (%) .|NOx (PPM)|
test...|meas|meas|meas| max|meas| max|meas| max|meas|
15 MPH |1725|14.5| 0.6|. 52|. 17|0.49|0.00| 424|1192|
25 MPH |1713|14.5| 0.6|. 36|. 16|0.46|0.00| 711|1437|


From all that I have read and in my conversation with the smog guy all the gases other than the NOx are excellent. No problem with ignition, airflow, or fueling is indicated. Just an EGR caused NOx problem.

Still no codes, so can the EGR not be working and not trip a light/code?

[canddmeyer]

Oh, the joys of living in California. Try another smog station. I've seen different results at different testing facilities. The real kicker here is the California EPA jerks introduced NOx testing after the vehicles were manufactured, and made the testing retroactive. The cars weren't designed with passing NOx testing or the manufacturers would have been more accomodating. Except for California, your beautiful car would pass a smog test in any of the other 49 states. I can only recommend trying another testing facility. Good luck.

[KeepItSimple]

Yes try another Smog place. My mechanic has a list of local smog shops here in Sacramento with pass and failure statistics. It ranged from an 85% pass rate to an 85% failure rate depending on which shop you went to!
And don't go by the franchise either. The 85% pass and failure rates were from 2 different Smog Express shops here in town. I go to the one with the 85% pass rate and pass every time.

[modian]

Thanks for the help. What puzzles me is two years ago on my smog test (with the original O2 sensors) the HCs were at the max (because it needed new plugs/wires), but the NOx level was really low. I'm sure there's an EGR issue playing here if these measured numbers *are* correct. Just no codes to start my troubleshooting.