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Somehow the new sensor massively reduced the CO as well. I’ll put the passing results below, but the last smog check before my diagnosis had CO readings of 1.10% and 0.82%. HC on that test was 97 ppm and 68 ppm, and there was zero O2.
15 mph:
1812 rpm
CO2 13.90%
O2 1.43%
HC 54 ppm (max 55 ppm, avg 9 ppm)
CO 0.05% (max 0.50%, avg 0.03%)
NO 56 ppm (max 437 ppm, avg 67 ppm)
(lambda = 1.065, lean)25 mph:
1773 rpm
CO2 13.90%
O2 1.44%
HC 22 ppm (max 39 ppm, avg 6 ppm)
CO 0.01% (max 0.48%, avg 0.03%)
NO 15 ppm (max 724 ppm, avg 62 ppm)
(lambda = 1.068, lean)I was a little suspicious when I got that diagnosis as well (and fearful that I’d immediately receive a P0420), but I think I subsequently read a claim that the downstream O2 sensor can have a small influence on the fuel mixture. Perhaps it’s not so much that it hampers fuel economy or driveability, but it’s just enough to make the computer target a fuel mixture that’s just outside the catalyst’s optimal range. Just curious–does that seem plausible at all?
I think I occasionally hear an exhaust leak, anyway. I don’t have a great ear for these things, but sometime I’ll try to look harder for one.
Somehow the new sensor massively reduced the CO as well. I’ll put the passing results below, but the last smog check before my diagnosis had CO readings of 1.10% and 0.82%. HC on that test was 97 ppm and 68 ppm, and there was zero O2.
15 mph:
1812 rpm
CO2 13.90%
O2 1.43%
HC 54 ppm (max 55 ppm, avg 9 ppm)
CO 0.05% (max 0.50%, avg 0.03%)
NO 56 ppm (max 437 ppm, avg 67 ppm)
(lambda = 1.065, lean)25 mph:
1773 rpm
CO2 13.90%
O2 1.44%
HC 22 ppm (max 39 ppm, avg 6 ppm)
CO 0.01% (max 0.48%, avg 0.03%)
NO 15 ppm (max 724 ppm, avg 62 ppm)
(lambda = 1.068, lean)I was a little suspicious when I got that diagnosis as well (and fearful that I’d immediately receive a P0420), but I think I subsequently read a claim that the downstream O2 sensor can have a small influence on the fuel mixture. Perhaps it’s not so much that it hampers fuel economy or driveability, but it’s just enough to make the computer target a fuel mixture that’s just outside the catalyst’s optimal range. Just curious–does that seem plausible at all?
I think I occasionally hear an exhaust leak, anyway. I don’t have a great ear for these things, but sometime I’ll try to look harder for one.
Time for an update! The car just barely passed. A professional diagnosis pointed to at least a faulty downstream O2 sensor, so I put a new Denso in there and re-checked. CO went down to normal levels, and HC came down a bit from this other shop’s first test but was still elevated (at 15 mph, just 1 ppm under the cutoff). There’s about 1.4% O2 in the exhaust now, and my fuel trim numbers seem to have adopted the pattern expected of a vacuum leak. Before this diagnosis and repair, I’d also started to hear an occasional exhaust leak in city driving.
So I’m good with the state for another two years, but perhaps I should try to make sure the catalyst doesn’t get ruined by the elevated HC. Other than checking the spark plugs for evidence of burnt oil, what might I consider? (The car loses some oil between changes, but at least some of that seems attributable to leaks.)
Time for an update! The car just barely passed. A professional diagnosis pointed to at least a faulty downstream O2 sensor, so I put a new Denso in there and re-checked. CO went down to normal levels, and HC came down a bit from this other shop’s first test but was still elevated (at 15 mph, just 1 ppm under the cutoff). There’s about 1.4% O2 in the exhaust now, and my fuel trim numbers seem to have adopted the pattern expected of a vacuum leak. Before this diagnosis and repair, I’d also started to hear an occasional exhaust leak in city driving.
So I’m good with the state for another two years, but perhaps I should try to make sure the catalyst doesn’t get ruined by the elevated HC. Other than checking the spark plugs for evidence of burnt oil, what might I consider? (The car loses some oil between changes, but at least some of that seems attributable to leaks.)
That might be the case for a lean exhaust generally, but I have a rich exhaust. However, O2 was also zero when I passed two years ago with numbers closer to those averages. (CO2 was higher at 15.0% on both speeds.)
That might be the case for a lean exhaust generally, but I have a rich exhaust. However, O2 was also zero when I passed two years ago with numbers closer to those averages. (CO2 was higher at 15.0% on both speeds.)
Yes, definitely insisting on an OE sensor next time.
Meanwhile, I had a chat with my mechanic from earlier. He thought the fuel trim might suggest a vacuum leak as well, perhaps at the intake gasket. However, that might have to wait for a smog shop’s diagnostic procedures. I can’t spray it accurately from above and don’t have a propane tool handy, but I may try with soapy water (as in some other videos) from under the car if there’s good access.
Yes, definitely insisting on an OE sensor next time.
Meanwhile, I had a chat with my mechanic from earlier. He thought the fuel trim might suggest a vacuum leak as well, perhaps at the intake gasket. However, that might have to wait for a smog shop’s diagnostic procedures. I can’t spray it accurately from above and don’t have a propane tool handy, but I may try with soapy water (as in some other videos) from under the car if there’s good access.
This same 5S-FE engine in the Gen 3 Camry had a distributor, but the Gen 4 (1997-2001) uses a distributorless wasted spark system.
I could try Sea Foam sometime if I can be absolutely certain it won’t harm anything, but aren’t fuel system cleaners like Techron supposed to clean the intake valves as well?
This same 5S-FE engine in the Gen 3 Camry had a distributor, but the Gen 4 (1997-2001) uses a distributorless wasted spark system.
I could try Sea Foam sometime if I can be absolutely certain it won’t harm anything, but aren’t fuel system cleaners like Techron supposed to clean the intake valves as well?
Test results are there already. Probably can’t do CAP even if I wanted (limit goes up to $650 on Monday, too, I think). Tried that website initially, but I believe all five things (air filter, O2 sensor, MAP sensor, TPS, and ECTS) are fine on this car.
I’ll check those other possible vacuum leaks… sometime when it’s not 108 degrees outside, anyway. Considering the potential fuel trim issue, a vacuum leak interfering with the fuel pressure regulator would be an interesting idea. However, I don’t see that mentioned on the vacuum hose diagram.
Test results are there already. Probably can’t do CAP even if I wanted (limit goes up to $650 on Monday, too, I think). Tried that website initially, but I believe all five things (air filter, O2 sensor, MAP sensor, TPS, and ECTS) are fine on this car.
I’ll check those other possible vacuum leaks… sometime when it’s not 108 degrees outside, anyway. Considering the potential fuel trim issue, a vacuum leak interfering with the fuel pressure regulator would be an interesting idea. However, I don’t see that mentioned on the vacuum hose diagram.
That’s the method I used, in fact… perhaps I’ll try a propane torch, especially around the fuel rail and intake gasket. (For what it’s worth, there is a fair amount of black gunk on that part of the intake manifold and fuel rail, too, including on the plastic electrical connectors to the injectors.) But I have also read that a vacuum leak will affect things more at idle than under load–and it’s under load where I’m having more trouble. Can you explain how the vacuum leak would work in this situation?
That’s the method I used, in fact… perhaps I’ll try a propane torch, especially around the fuel rail and intake gasket. (For what it’s worth, there is a fair amount of black gunk on that part of the intake manifold and fuel rail, too, including on the plastic electrical connectors to the injectors.) But I have also read that a vacuum leak will affect things more at idle than under load–and it’s under load where I’m having more trouble. Can you explain how the vacuum leak would work in this situation?
