Tailpipe Emission Test Failed

My car failed emission test. My mechanic seems has much clue to narrow the potential cause.

1995 Toyota Camry V6 225,000 miles. CO:1.23 Limit:1.10, HC: 771 Limit:275, NO:4113 Limit: 3600, RPM 1730, 14.5%

Emission Control System Inspection:

Air Inj. System: N/A, EGR System: Pass, PVC System,Catalytic Converter, Evaporative Control System,Fuel Inlet Restrictor received pass.

Can anybody suggest what to check?

Before you can keep emissions under control, the engine must be operating perfectly mechanically. With the miles on the engine, it may be worn to the point that no matter what you do, it’ll never pass.


Your running way rich, causing the failed emissions. First thing I would check is the fuel pressure. Make sure it is within specs. Then check the spark plugs, wires, distributor, and coil. Mis-fires will send unburnt fuel down the exhaust, mimicking a rich condition. Also, when was the last tune-up? And, when was the last time the O2 sensor was replaced? On this model, I believe it should be replaced every 30,000 miles. The engine management computer adjusts it’s fuel trims based on the O2 sensor output. Bad data from the O2 sensor can cause a rich condition.

Could be broken seals where the injectors go into the holes. Could also be bad everything.

Thanks for the info. I wonder how difficult to find the culprit(s)? Is there any computer analysis system for finding the problem or you need to change parts one by one? Based on the comment they made when the emission test was failed, they are predicting hours to check the. Naturally, the garage is charging based on the hours they spent to fix the problem. I suppose a good mechanic could be able to pin point the cause in shorter time. Should I bring to a more capable garage which is 30 min. farther than this one or a Toyota dealer?

Just start simple: change the spark plugs and air filter. Now, how smoothly does the engine idle? If much smoother, take it back for retest. If not smoother, change the spark plug wires. Results? If smooth, retest. If not, your mechanic needs to dig deeper.

The way high HC is the thing that stands out to me and this can affect the other two.
High HCs can be caused by the state of tune (plugs, wires, etc.), faulty injector spray pattern, filthy air filter, and even things like retarded ignition timing or a partially clogged converter. (and a converter can be partially clogged no matter what the test shows)

The car has 225k miles and if it’s burning a little oil then I agree with Tester that you’re beating your head on the wall because the oil consumption could be behind the high HC problem.

I wonder what’s up, considering the high HC and the NOx over limits. I mean, HC suggests rich, but I was under the impression NOx was caused by high combustion temps…and running way rich should keep things cool, at least. (Speaking theroy only–by the time I knew enough about cars to make sense of a sniffer test, I was in the OBD-II era.)

How about pulling the plugs, reading them, and having a compression test done while they’re out? I agree w/ Tester: if it’s a worn engine, one might be SOL, so best to find that out before too much money is sunk into repairs.

Your PRIMARY problem is MISFIRE. That produces the high HC, hydrocarbon, which is UNBURNED fuel. Have a MECHANICAL compression test performed and it that checks out OK, plugs, wires, injector cleaner…

That’s what I was looking at. High HC’s, CO, and high NOx readings? The only thing that can cause that is, each cylinder is doing it’s own thing.


I’ve changed oil, oil filter and dirty air filter. I also used fuel injector cleaner. But I have no idea of changing spark plugs on Camry V6 although I’d changed spark plugs on old Honda Accord 4 cylinder number of times. They look quite different. I might need to ask a mechanic to do the job. I’ve also noticed that oil is seeping out from head gasket area. Does this indicate possibility of burning oil? I’ve been using high mileage engine oil.