[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.