Failed California smog third time?

Hello,

I'm going to need a little more info on what you have done to try and remedy your emission issues....

Emissions, especially on OBD1 cars, can be tricky to nail down. With the age and mileage of your engine, have you verified the engine itself is in good condition?

I would perform a compression test, as well as a cylinder leak down test to see how the general health of the engine is doing. Tools for this can be found very reasonably at Harbor Freight, Amazon, etc...

Leak down test especially will let you know how blowby, valves, etc., are doing.

Worn valve guide seals letting excessive oil into the combustion chamber could even cause an emission failure.

High HC is indication of incomplete combustion (rich fueling).
NOx is a product of high combustion temperatures (check timing advance).

How is the O2 sensor doing? Is it responding quickly and showing a change from rich to lean quickly?

Before getting too deep in the woods, please provide further info on what you have done thus far, and results of any diagnostics you have performed.

Thanks,

Jason

Hi,

That is an odd one. The significant changes in hydrocarbon (HC) and nitrogen oxide (NOx) emissions between 15 MPH and 25 MPH during a dyno test can be indicative of various possible issues.

The drop in NOx at 25 MPH could indicate that the catalytic converter is working better at higher speeds. Also, a malfunctioning oxygen sensor can lead to incorrect fuel mixture and affect emissions. Differences in speeds may cause variations in sensor readings. Have you checked the oxygen sensor voltages? Are there any engine vacuum leaks or exhaust leaks?
There are many other possible causes.

What has been done at this point? Are there any diagnostic trouble codes stored or pending? Do you have a live data scan tool that we can use to check fuel trims, Oxygen sensor voltages, and other data? If you have a live data scan tool, check what the short-term fuel trims are at operating temperature. Also, note each oxygen sensor's voltage readings and let me know.

Let me know. Also, let me know what has been done to date.

Joe

Hi Joe. Great feedback. I must admit I have gotten in over my head at this point.
Do not have enough diagnostic tools for this fine tuning.
Engine rebuilt 50,000 miles ago. I took the head taken off last month and replaced valve seals and lapped the valves. 195-200 PSI compression on all cylinders.
Cleaned And checked EGR for correct function per FSM as well as EGR regulator.
Not many vacuum lines on this engine. They all appear good.
New 02 sensor, catalytic converter, gaskets on intake and exhaust.
Runs absolutely great. Idle is smooth. Timing is dead on. Evap system checked.
Fuel pressure regulator is the only system I have not checked.
New oil 5w30 synthetic. New air filter.
No fault codes show up in OBD1 blinking check engine light test.
Test results have gotten better each of the three times as I go through each system.
Need to study up on fuel trims and checking O2 sensor voltage. There is a vacuum actuated fuel pressure regulator I have not touched.

Thank you, Jason. Hope my response to Joe answered your questions for me.
Fuell pressure and O2 sensor research today.

Hi,

You must still have the OBD1 system. In 1995, they started changing over to the OBD2 system. To get live data, you would need a scanner that can work with the OBD1 system.

As far as the fuel pressure regulator, remove the vacuum hose with the engine off. Check for any evidence of raw fuel being present. If there is, replace the regulator. Also, if you have a chance, let me know what the pressure is.

Also, here is a link that you may find of interest and helpful:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Take care,

Joe

PS: I'm going to mention this to the site owner. He is in CA and likely knows a lot more than me about the emission testing procedures there.

Will check those two things tomorrow.
I know I am close by the low readings I am getting. Way under maximum.