Fake emissions test

[ConnClark]

Originally Posted by cfg83

But that seems to go back to the original question. The observed readings were identical for both tests.

Do you think that, based on the size of the leak + the accuracy of the readings yielded an accidental co-inky-dink of identical readings?

CarloSW2

I think that the leak was small enough that it wouldn't have an effect on the readings. Unfortunately it was big enough for them to detect it and use it as an excuse to fail the car.

[TestDrive]

I agree with ConnClark, the leak was small enough that it would be unlikely to have a measurable effect on the emissions numbers.

For the rpm numbers to match, you either have to believe that Bubba retrieved the test from machine memory (didn't think that was even possible until yesterday*) or you have to believe in coincidence - but not a huge coincidence - Bubba probably used the exact same, fixed length stick to prop the throttle open for the high-idle portion of the test.

Even if you believe Bubba retrieved the emissions numbers, the numbers would have to right at the failing limit before you could believe that repairing such a small leak might have changed the test results in a meaningful way.

Just out of curiosity, what are the rest of the numbers on your test results anyway?

*Yesterday morning while tracking down references for the debate with ConnClark, I read the Texas statutes defining what inspectors must or must not do. One of the provisions specifically forbade them from retrieving the emissions numbers of previous tests for reuse in final certification of a vehicle. Evidently some test equipment allows that.

[streeter]

Originally Posted by ConnClark

You did not fail for a safety reason

An exhaust leak by itself is not a safety issue unless it leaks or is directed into the passenger compartment.

You failed because it was not possible to give an accurate emissions test. In the US emissions are measured on a grams per horsepower ratio. If you have an exhaust leak it allows some emissions to escape their collection and detection instruments. This will reduce the grams per HP measured and if a big enough leak occurred it would allow a car that would fail to pass.

Moral of the story: if you can make a big enough leak that they can't detect or fits in a loop hole you will always pass.

On the saftey thing, True but not. It boils down to local regulations. In utah I CAN and HAVE failed cars for exhaust of saftey. If the exhaust does not exit the passanger compartment of said vehicle it fails.
Now onto emission test, the computer gives you parameters of pass and fail. On dyno they give you Hc's, co's, O2, co2's and nox, on OBD2 it is all plug and play. I have seen many cars run like crap and they passed both test! can I do anything about it.....kindof.

Like Daox said, if you are concered about lowing your total emission have a 5 gas test run. That will give you accurate readings (for those speeds) of your vehicle output.

P.S. My old 85 ford f-250 pickup run on a dyno (I don't have to do it that way) puts out less pollution then most 2000 plus vehicles. My nose tells me it runs like crap but the dyno says it runs like a dream

[JasonG]

Most test shops partially block the tail pipe. Any whistling means there is a leak that must be fixed for safety reasons.
I assume you have a sedan. The DOT law states that all exhaust must exit behind or above the passenger compartment.
Even if you dont feel the leak is entering the passenger compartment because your windows/floor/etc is sealed, it is still a hazard.
Bottom line, you had a dangerous exhaust leak and fixed it. You are safer now. The actual gas emissions are really irrelevant.

[windrider919]

I do not know HOW the tailpipe emissions probe can detect an exhaust leak but just after Hurricane Ike in Alvin Texas (just a few miles outside of Houston so we have to do the extended test) my 1995 Dodge Dakota w/ v6 failed for that reason. I stood in the bay doorway as he hooked up the truck. A cable lead to the ECM socket in the engine compartment and then a test probe into the exhaust pipe. He failed me before the first test would even run and said I had a exhaust leak and the machine would not even go further in the test. Somehow the machine senses it is not getting enough exhaust. We looked from one end of the car to the other, blocking the exhaust to make any leak increase/whistle but found nothing. He had other cars to do so I had to leave with a failure strip.

A couple of days later I took the truck to another shop run by a friend that had previously been closed because Ike had torn off part of their roof and soaked their testing machine. He had told me it would be weeks before it got repaired so I had gone elsewhere but it got fixed right away. Again my truck would not even test and showed exhaust leak. Note: the idle RPM was within 5 RPM of the previous test, the machine controls the throttle.

We searched the truck exhaust from tailpipe to headers and found nothing again. But one of the guys looking into the engine compartment noticed one of the plug boots was slightly blacker than all the others. And there was the exhaust leak. A tiny pinhole in the exhaust manifold gasket. Even seeing it no one could hear it, even with the exhaust blocked by a rag in the tailpipe.

And this part will make you laugh. The good ol boy country repair! We used some of the foil from a stick of gum and a awl to push it into the minuscule hole! Packed it tight and the analysis machine gave me a pass. I drove the truck till two weeks ago when I traded that 14 year old, 208,000 mile machine in for a 2006 Ford F150. The gum wrapper plug was burned and oxidized where it showed but still in the hole, doing it's job! [Did I mention I am an aircraft mechanic? Worked on many Boeing n McDonnell-Douglas heavys. I have stories to tell about duc tape that will make your hair turn gray / an you will never fly again! In the aviation industry it is called 200MPH tape. Us'n country boys cun fix ANYTHING with gum n duc tape!!! An sometimes I have worked as a contractor at NASA as a Millwright too!]

The point of the story is that SOMEHOW the test machines CAN detect exhaust leaks.