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Unread 05-29-2013, 06:58 PM   #1
badluck1984
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Join Date: Mar 2013
Location: redwood city, CA
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tstat ecm open close loop explanations?

Can someone please explain how all this works?Is it possible for a 165 tstat to cause the ecm to not supply enough fuel at 15 and 25 mph thus a hi nox reading in a smog test?

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Unread 05-29-2013, 08:11 PM   #2
jsawduste
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2006 YJ Wrangler 
 
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A simplistic answer
http://autorepair.about.com/library/...bldef-109a.htm

Yes if the engine does not each operating temperature then the ECM calibrations will effect the NOX readings. I have done a number of dyno runs with the 4.0 based engines and they like heat. Power output at 200 degrees vs. 210 shows an increase in efficiency at the higher temperature. Stock these engines came from the factory with 195 thermostats. Running anything less will lower performance and increase emissions.

On my stroker (equipped with a 195 stat) and an electric fan the engine temperature would cycle from 210 down to 180. The ECM was constanly trying to re-adjust for the temperature swing. Changing back to a stock fan, clutch and shroud coupled with a Hesco brass 3 row radiator has the engine running at a steady 180. Whether in traffic or on the freeway. The ECM is now in a steady mode compared to what it used to be and the engine runs much better. My only compliant is that it now runs a little to cool. I`s like to see another 20 to 30 degrees to optimize the calibrations.
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Unread 05-30-2013, 01:16 PM   #3
badluck1984
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Would the cold stat cause it to run rich not lean?
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Unread 05-30-2013, 04:17 PM   #4
jsawduste
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Quote:
Originally Posted by badluck1984 View Post
Would the cold stat cause it to run rich not lean?
Yes
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Unread 05-31-2013, 10:22 AM   #5
Que89YJ
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During cold start the ecu is running rich both to protect the engine and to get fuel into the catalyst to get it hot enough to deal with Nox. If it stays in cold loop with an engine temp below 180 it will continue to run rich and not go into the closed loop and use the output of the O2 sensor to repspond to the calibration. If you have high nox it is usually a lean condition not rich and you look at fuel pressure, the manifold air temp sensor(MAT) and Coolant Temp Sensor(CTS)(Both are used for injector pulse width) and your Catalyst.
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Unread 05-31-2013, 01:26 PM   #6
jsawduste
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Quote:
Originally Posted by Que89YJ View Post
During cold start the ecu is running rich both to protect the engine and to get fuel into the catalyst to get it hot enough to deal with Nox. If it stays in cold loop with an engine temp below 180 it will continue to run rich and not go into the closed loop and use the output of the O2 sensor to repspond to the calibration. If you have high nox it is usually a lean condition not rich and you look at fuel pressure, the manifold air temp sensor(MAT) and Coolant Temp Sensor(CTS)(Both are used for injector pulse width) and your Catalyst.
My yes answer was based on the cat not lighting off. Thanks for explaining it the the OP a bit further. Have the OP generate some BTU`s and then see what the NOX values are.
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