All LS400 owners with bad gas mileage READ THIS!
02-20-11, 08:33 PM
#121
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i, too, changed the ect sensor (autozone for convenience) after reading this thread. car seems to shift smoother, but haven't driven much to notice any significant difference. filled the tank so i'll test out the mpg thing in coming days. old ect sensor was a wreck. corroded, brittle, rusted, in fact it broke off while taking it out.
02-20-11, 08:49 PM
#122
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I noticed that it was taking forever for my 95 ls to warm up early this winter. On colder days, the idle wouldn't drop below 1500, and it took forever to get to 1000 Rpm. After much research and watching my mpg drop to 16-17, I decided it was the ECT. Quick 1 hour service at my mechanic and it was replaced.
Now, cold start idles initially at 2,000, then drops to 1700 after 30-45 seconds. Engine temp hits first line after driving 20mph for 45-60 seconds and the idle drops again to 1200. After 2-3 minutes on 35F morning, the temp gauge hits the second line and the engine drops to 700-900rpms. Another 30-ish seconds and the engine temp hits the middle line and idle drops to 300-500rpms. (A/C compressor kicks it up a bit from there but not much.)
This all resulted in me averaging 20.5mpg in mixed driving, and a more relaxing drive in traffic as I don't have to fight the high idle anymore.
Now, cold start idles initially at 2,000, then drops to 1700 after 30-45 seconds. Engine temp hits first line after driving 20mph for 45-60 seconds and the idle drops again to 1200. After 2-3 minutes on 35F morning, the temp gauge hits the second line and the engine drops to 700-900rpms. Another 30-ish seconds and the engine temp hits the middle line and idle drops to 300-500rpms. (A/C compressor kicks it up a bit from there but not much.)
This all resulted in me averaging 20.5mpg in mixed driving, and a more relaxing drive in traffic as I don't have to fight the high idle anymore.
02-21-11, 04:42 AM
#123
well, i changed the rear two o2 sensors this morning and the fuel filter. so far so good. exhaust doesnt smell like gas anymore, and i went driving around town. 10 miles or so. romped on it several times. engine light has not come on at all which is another good thing. it was coming on before saying lean even though it wasnt. my last tank of gas was 16.1mpg. i filled up on the way home and reset the trip meter. ill fill up at 300miles and see how it does.
02-21-11, 07:19 AM
#124
Pole Position
Nice to hear you finally got those rear O2s in. 
I don't understand how they can help the MPG but hey, if it works that's great. It would be nice to see 500 for the tank, you've been fighting it for a while now. Let us know what ya get b/c I know I need to do something with mine also. I'm only seeing about 14 MPG, 
but I have other things wrong with it too.
02-21-11, 10:46 AM
#125
well, i literally changed everything else. front o2 sensors, ect sensor, cleaned the egr system out and made sure its working, plugs, valve job, etc.... ive spent more on repairs so far then i did on the car, and ive had it less then a year. also, i noticed i need front lower control arm bushings. old rack was leaking and you can see the bushings swelled up and bulging out of the arms in the front crossmember. grrrrrr.
02-21-11, 11:12 AM
#126
Pole Position
well, i literally changed everything else. front o2 sensors, ect sensor, cleaned the egr system out and made sure its working, plugs, valve job, etc.... ive spent more on repairs so far then i did on the car, and ive had it less then a year. also, i noticed i need front lower control arm bushings. old rack was leaking and you can see the bushings swelled up and bulging out of the arms in the front crossmember. grrrrrr.
You put so much time and money in it to try and save some gas, you'll never gain back the amount you put in. But it's like a new car so I'd bet it's worth it. It's like when my union went on strike, we were out for 8 months just to get another $1 an hour. 
It's gonna take 17 years to make up what we lost in our check, but we gain in retirement. Life, give a little now to gain in the end. I can't wait for that. LOL
02-21-11, 11:22 AM
#127
idk, i drive 400+ miles a week. an extra 200 miles per tank will add up quick! 20,800/300= 69.33 fillups. 20,800/500= 41.6 fillups. thats a difference of 27.73 fillups at $60ish each which comes to $1,663.80 a year. so yeah. itll be worth what ive done. the things i did soley for gas mileage was the 4 o2 sensors, the ect sensor, and plugs etc.. thats less then $200. and with gas prices still climbing, itll be even more benificial later on.
02-21-11, 11:41 AM
#128
Pole Position
Oh, definately. That's the thing with the internet, ya can't see a sense of humor. I know you'll save it in the long run. Especially the way you buy the parts, $120 for all 4 O2s is awesome. Other people spending 120, 130 a pop for the same thing, crazy. I remember driving all them miles for work (730+ a week) but I drove a 6 cylinder back then, trying to save every penny. GL
I know you'll save it in the long run. Especially the way you buy the parts, $120 for all 4 O2s is awesome. Other people spending 120, 130 a pop for the same thing, crazy. I remember driving all them miles for work (730+ a week) but I drove a 6 cylinder back then, trying to save every penny. GL
02-21-11, 06:04 PM
#129
well, on the way home the damn engine light came back on. code 25 again. at this point it has to be the ecu thats the problem. and this is the 2nd ecu already. grrrrrrrrrrr
02-24-11, 06:29 AM
#130
filled up this morning and confirmed im still only getting 16mpg with 90% highway driving. this sucks. if gas keeps going up ill have to go back to driving my beater which gets 25-26mpg. might even look for a diff rear end for it to increase it even further. swapping from a 4.10 to a 3.73 will prolly put it at 30+ mpg.
02-24-11, 05:02 PM
#131
Pole Position
filled up this morning and confirmed im still only getting 16mpg with 90% highway driving. this sucks. if gas keeps going up ill have to go back to driving my beater which gets 25-26mpg. might even look for a diff rear end for it to increase it even further. swapping from a 4.10 to a 3.73 will prolly put it at 30+ mpg.
02-24-11, 05:19 PM
#132
i know. looks like ill be parking the ls soon and driving the beater instead. hell, it gets 10 more mpg. and at 80 miles a day that adds up quick. $100 a month less in gas. and if i can find a 3.73 diff for the beater, itll prolly go to over 30mpg.
03-01-11, 06:26 PM
#134
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My gas mileage on my 1991 LS400 was averaging 16 miles to the gallon. I had replaced oxygen sensors,wires,plugs,cap,rotors,thermostat,throttle body cleaning with no improvement. After studing ECU theory, I found out the Coolant Tempurature Sensor is the "MAIN SENSOR" for the computer. This sensor has more control over the computer than any other sensor. To make a long story short, my COOLANT SENSOR was telling the computer it was -20 degrees farenheit(thats minus 20 degrees) and no check engine light. Cost of new sensor was 50 dollars. I now get 23 miles to the gallon higway with a light foot. I now save 650 dollars a year in gas driving 12000 miles a year and I can feel the 250 horsepower when I open it up. If you have an old LS400...CHANGE THIS SENSOR!!
03-01-11, 06:27 PM
#135
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i, too, changed the ect sensor (autozone for convenience) after reading this thread. car seems to shift smoother, but haven't driven much to notice any significant difference. filled the tank so i'll test out the mpg thing in coming days. old ect sensor was a wreck. corroded, brittle, rusted, in fact it broke off while taking it out.