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All LS400 owners with bad gas mileage READ THIS!

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Old 09-03-08, 10:26 AM   #16
jasonburt
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Their are 3 coolant sensors on the LS400. One is for the fuel and timing maps on the computer. One is for a timer for the cold start injector. One is for the tempurature guage on the instrument cluster.
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Old 09-03-08, 06:10 PM   #17
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Are there any other symptoms of a bad coolant sensor besides poor fuel economy? My 93 LS does great on the highway (25+), but bad in town, last tank 12 and I don't drive it hard.
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Old 09-03-08, 07:00 PM   #18
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This test is not completely trustworthy. The ECT sensor operates dynamically like an oxygen sensor. This is a static test. It does not tell you how fast the sensor reacts to changes in tempurature. As these sensors age they may take 30 minutes to tell the computer your engine is hot..or may not ever tell the computer your engine is hot at all. This sensor is like an oven thermometer..it's trapped in all the heat under those engine covers and when it bakes over the years it becomes flaky, just like the thermometer in your oven, in your house. I'm going to look into the EGR temperature sensor as well
dont know what you are trying to say but its from the manufacturer so i believe it helps to determine if the sensor is still working or not. and this is the very first thing we want to know to decide if we need a replacement

back to your comments, engine temp increases gradually and never suddenly, do we really need a fast reacted sensor here?

purpose and application of oxygen sensor is completely different from ECT, oxygen sensor must (and is able to) react fast. oxygen sensor testing procedure is no way similar to that of ECT sensor
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Old 09-04-08, 12:21 PM   #19
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Quote:
Originally Posted by qha_vn View Post
dont know what you are trying to say but its from the manufacturer so i believe it helps to determine if the sensor is still working or not. and this is the very first thing we want to know to decide if we need a replacement

back to your comments, engine temp increases gradually and never suddenly, do we really need a fast reacted sensor here?

purpose and application of oxygen sensor is completely different from ECT, oxygen sensor must (and is able to) react fast. oxygen sensor testing procedure is no way similar to that of ECT sensor
Does anyone know what the feedback setup of the ECT sensor is? Is it a simple resistance that it provides?

I'm trying to find a way to avoid cold start behaviour my car. (Fuel dump, and high rpm) Maybe one could install a resistor so that ECU gets hot engine signal always. Anyone experienced in this area?
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Old 09-04-08, 06:17 PM   #20
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Originally Posted by qha_vn View Post
dont know what you are trying to say but its from the manufacturer so i believe it helps to determine if the sensor is still working or not. and this is the very first thing we want to know to decide if we need a replacement

back to your comments, engine temp increases gradually and never suddenly, do we really need a fast reacted sensor here?

purpose and application of oxygen sensor is completely different from ECT, oxygen sensor must (and is able to) react fast. oxygen sensor testing procedure is no way similar to that of ECT sensor
With gasoline @ $4.00/gal you would want a sensor that operates at peak efficiency. That is, unless fuel cost and performance is not a concern.
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Old 09-04-08, 07:21 PM   #21
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Bali,

The ECT is a thermistor. It varies resistance with changing temurature. It works with a 5V referance with the computer. The thermistor is part of the divider circuit on the computer which varies the voltage from 1v to 5v. 5v=rich fuel mixture with retarded timing.
1v=lean fuel mixture with advanced timing.
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Old 09-04-08, 07:36 PM   #22
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With gasoline @ $4.00/gal you would want a sensor that operates at peak efficiency. That is, unless fuel cost and performance is not a concern
Agree that some may replace the ECT sensor without a need to know if its still good or bad. i would love to replace whatever contribute to the car perfomance & mileage: spark plug, wires, all engine sensors, all distributor components... without a need to know if they are still okay or not. and after all, i will replace my 90LS400 with a LS600h :-D

thats why all car makers provide repair manual
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Old 09-04-08, 08:24 PM   #23
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Quote:
Originally Posted by jasonburt View Post
Bali,

The ECT is a thermistor. It varies resistance with changing temurature. It works with a 5V referance with the computer. The thermistor is part of the divider circuit on the computer which varies the voltage from 1v to 5v. 5v=rich fuel mixture with retarded timing.
1v=lean fuel mixture with advanced timing.
Thanks Jason,

Then how can I rig the ECT sensor to send constant 1v?

Easy as connecting the two wires?
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Old 09-04-08, 09:02 PM   #24
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Everyone who has replaced this part or is going to, please let us know your MPG improvement. I get about 19mpg average, but with different driving I can get up to 23 in my '94.
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Old 09-04-08, 10:16 PM   #25
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Bali,

100 ohm resistor would = 1v. any less than 100 ohm might smoke your computer. This wouldn't be wise because your car will have cold start problems.
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Old 09-04-08, 10:19 PM   #26
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changing mine tomorrow..
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Old 09-12-08, 10:02 AM   #27
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So, has anyone else seen any results from replacing the coolant sensors?
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Old 09-12-08, 11:04 AM   #28
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Mine was corroded to hell and the sensor was actually detached (broken) from the metal but did not throw an error code. Go figure.

Anyways, I replaced mine, I noticed smoother idle and some pep to the throttle response (I did not pull the ECU fuse because I didn't want the reset throwing off any results). I am still calculating my first full tank of gas to see the MPG improvement. I don't exactly trust the accuracy of my fuel gauge at the moment.
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Old 09-12-08, 08:02 PM   #29
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I am still confused on which sensor is being replaced.

Are you guys talking about the one on the top of the block which I don't know where it is, or are you talking about the one in the bottom of the radiator?
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Old 09-14-08, 05:25 AM   #30
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You can get them from rockauto.com for $20-$35 depending on which sensor manufacturer you opt for.
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Old 09-14-08, 05:25 AM
 
 
 
 
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91, bad, box, coolant, ecu, forum, fuse, gas, lexus, ls400, mileage, oxegen, sensor, seville, temp, thermometer

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