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Re: Failed Emissions - Follow up Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 21 Jun 2001 11:10:01
In Reply to: Failed Emissions - Follow up, Jim Foley, Thu, 21 Jun 2001 09:08:15 Members do not see ads below this line. - Help Keep This Site Online - Signup |
It is most definately NOT safe to plug in an AMM with different dash number (last three digits). For some unknown reason (they had a big box of connectors?) Bosch changed the wiring with different AMM part numbers, but kept the same connector. The plug will fit, but you can burn up the AMM, the Engine Control Unit (ECU), or both. The plugged adjusting screw type is different (Saab used them in later years), and I know for a fact that the older and newer units will do damage if plugged into the wrong car.
Frankly, the O2 readings at idle seem right. And those readings won't be right if the AMM is bad. The O2 sensor has about 25% authority on scheduling fuel, but the AMM has 100% authority. So if the AMM were bad, you'd see it at idle. Rarely do cars have the right mixture (as your readings seem to be), and they can be off a bit and the car will still pass.
Fixing the vacuum leak may do it. Operation under load is a lot different than idle, and that leak could have a greater affect at speed. But if everything else checks out, I have to agree that it may be the cat.
The reason the voltage on the O2 sensor swings back and forth is that the catalytic converter actually needs a rich and lean mixture to work. That's why it's called a 3-way converter. At lean it handles one kind of emission (HC? Can't remember), and at rich other kinds. All part of the wonderful chemical reactions that go on inside. If the mixture seems right, I'd have to say the cat may be bad.
Good luck!
, Thu, 21 Jun 2001 11:10:01 <-- Viewing This Message
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