93 Camry 3VZFE: Failed emissions

[hbasavar]

Hello,
93 Camry LE 3VZ-FE wagon
Problem: Emissions failed for the second time
First emission test, resulted in a CEL with code 28. Replaced the rear manifold O2 sensor with Bosch Universal part # 12031
Retest: Failed again with better values
25/25 test
==========
HC ppm - 119 allowable 117 : FAIL
CO % - 0.18 alowable 0.65 : PASS
NO ppm - 1230 allowable 821 : FAIL
RPM 1738 : PASS
CO+CO2 7.9 : PASS
50/15 test
==========
HC ppm - 73 allowable 120 : PASS
CO % - 0.07 alowable 0.67 : PASS
NO ppm - 855 allowable 907 : PASS
RPM 1729 : PASS
CO+CO2 7.8 : PASS
Any ideas what could be done?

By the way, the cat was replaced last year. Is it possible it could have gone bad again because O2 was bad and had to work extra hard? Any additives would help or should I replace the O2 universal with O2 OEM?

Thanks and appreciate your response.
Hemanth.

[dc_98_cam]

Check your air filter ... check your PCV.

Another thing to try ... Disassemble your EGR valve ... look for carbon buildup in all the tubes.
There is a flexible diaphragm which moves up and down ... see if you can move it freely with your fingers. .. If it is stiff or you detect sticking ... you might have to replace it.


Why did you replace the rear O2 sensor, as opposed to the ones in the front, before the catalytic converter?

Not sure if an OEM O2 sensor will actually make a significant difference in test results ... no personal experience .... OEM is probably quite a bit more expensive.

One thing to try just before you go in for the next retest ... find an empty highway and floor the gas pedal several times for a few seconds ... you don't have to build up speed, just let the engine rev up a few times.

Does your car have the OBD II diagnostic capability?

[hbasavar]

Originally Posted by dc_98_cam

Response from dc_98_cam ....

Thanks for your response. Air filter is clean and the PCV valve was also replaced.

The car was taken on a highway before going to the test.

I will check on the EGR valve. Not worth replacing this as it is an expensive part.

This car doesn't have the O2 sensor after the cat. Only CA vehicles have that. There are two O2 sensors on each bank on the exhaust manifold. I replaced the one on rear manifold as the CEL code 28 corresponded to that. It was burning coolant on the rear bank before the head gasket job and that explains why it went bad.

No OBDII diagnostics on this one. Only OBD I.

[Quicksilver300]

I'm starting to love NY, I dont even get my emissions tested.
It's more like yep, there's an exhaust; pass

From what I read, your problem is most likely, faulty cat, clogged egr, timing, spark plugs, a malfunction of the cooling system causing high combustion temps. All of the above could be causing high temps which create NO, except a faulty cat, being that doesnt have much to do with temps.

[hbasavar]

My radiator cap has worn out and sure the coolant is not pressurized. Would this cause the high cylinder temps with higher NOX emissions?

The coolant temp is still half way in the middle.

[dc_98_cam]

Originally Posted by hbasavar

My radiator cap has worn out and sure the coolant is not pressurized. Would this cause the high cylinder temps with higher NOX emissions?
The coolant temp is still half way in the middle.

Difficult to say for sure. You might have two separate problems going on.
One is excessive hydrocarbon emission ... not burning fuel efficiently.
Two, is excessive NOx emission.

The loose radiator cap could be the cause of the excessive hydrocarbon results ... due to lower engine temp ... in the vicinity of the cylinders.
Not sure what is going on with the dash gauge. I wouldn't trust it completely. It only measures the temperature at one point in the coolant system.

With the sealed radiator cap functioning properly, the coolant system pressure is about 30 psi absolute. With a defective/loose radiator cap, the system pressure is about 15 psi absolute. At 30 psi, the normal condition, you have a higher coolant temperature ... and more complete combustion and better efficiency. ...
At 15 psi, you will not be burning your fuel as efficiently as at 30 psi.

With the coolant system not being sealed, you will be gradually loosing water as a result of evaporation. Eventually, you will have enough coolant loss that your engine will overheat... probably in traffic during rush hour.

So, make a point of buying a new radiator cap, refill coolant reservoir with correct 50/50 antifreeze/distilled water mix.

Hope that the loose radiator cap was not a long term situation .... which might have created a problem.

Not sure about the NOx emissions.... I would investigate the EGR valve for carbon build up ... This is a frequent complaint reported on the forum posts. I think you can check the movement of the flexible diaphragm with the engine running ... just push it up and see if the engine returns to normal after a second. It might be a good idea to disassemble the EGR and see if you can clean up some of the accumulated carbon ... You're talking about several years of engine operation with a 93 model. There might to be a DIY sticky on this posted at the top of the forum page. ... There ought to be.