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Old 08-28-2004, 07:07 PM
vellosg1 vellosg1 is offline
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Join Date: Feb 2004
Location: The Woodlands, TX
Posts: 23
Thanks Duke 2.6 and also Gerryvz

Originally Posted by Duke2.6
This sounds like a typical case of the converter being too cold.

I assume you live in California?

Go to a drivethrough place with a short line after driving the car at least 15-20 minutes including a freeway hop, and drive it aggressively.

Keep the engine at 2000 revs in neutral with the AC on and the window/sunroof open to keep a load on the engine until the tech is ready to drive it onto the rollers.

Note that your 15 MPH O2 is 0.4% percent and only 0.1% at 25 MPH. This is the tipoff that the converter was too cold, and it could not use all the available oxygen to oxidize HC and CO. Likewise, a cold converter will not reduce NOx efficiently.

What were the conditions of your test? Did you just drop off the car and come back later? Did you wait, but shut off the engine?

I don't think there's anything wrong with your car. Mercs need proper "pre-conditioning" or a cold converter will bust the first test with the second test being okay because the converter heated up to proper temperature during the first loaded test. Owners need to be aware of this and properly "manage" their emissions test.

I've measured the converter inlet nipple temp on my car with an IR gun after a normal drive, and then after five minutes of idling. The measured surface temp dropped from about 600 to 300 F.

BTW is your engine a M104 twin-cam or the M103 single cam, and is it a KE fuel system or the later all electronic system with solenoid injectors. Sorry, but I can't keep all the various model/engine configurations straight.

Duke2.6 and Gerryvz gave similar replies to the thread, so I am answering both here:

I live in Houston, TX. I drove some 10 highway miles to get to the inspection site and the car got there fully warmed-up. However, I had to wait (car parked, engine off) for some 45 minutes. The inspector took the car for a 5 minute ride around the block before running the emissions test. Probably this was not enough to bring it to temperature.

What I intend to do next is to use the "guaranteed to pass" and discuss the issue with the inspector up-front (will bring print-outs of these threads), to be sure the car is tested at correct engine/catalyst temperature.

Hope it works!
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