Poor Mileage Even After Maintenance
09-01-17, 12:47 PM
#1
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Poor Mileage Even After Maintenance
Hey guys,
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
Last edited by bluefisher; 09-01-17 at 12:51 PM.
09-02-17, 11:27 AM
#2
Hey guys,
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
You could replace the Coolant Temp Sensor as well.
The 98-00 call for ~93 octane and iridium spark plugs. NGK are always a good choice.
my 98 has a ton of miles and fuel mileage for me is usually around 17city 24 highway
also , if you haven't cleaned the air mix path(on the throttle body), I definitely recommend it. That could be part of your issue as well.
09-03-17, 10:50 PM
#3
Lexus Champion
Hey guys,
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
Got a 99 LS400 from a friend at 149k miles earlier this month. Decided to do some maintenance on it and I could use some advice. My mileage is horrendous. The "RANGE APPROX" would drop 2 miles per mile. It was driving me nuts. I wanted to fix this as even general use was poor.
To start I changed the brakes, air filter, cleaned the MAF and intake, changed sparks and even seafoamed the sucker. Results? Mileage is worse and the car lost power. I get city mileage on the highway now. I'm thinking it was due to the sparks because I used Autolite copper (I know), which should have provided better performance. I just don't feel the V8 anymore and the idle isn't as quiet for some reason. Requires more effort on the pedal.
Two of the coils had the screws seized but I did the install anyways and secured them down. Don't think that would affect the performance but I'm thinking it was the replaced spark plugs that are causing it? Cleaning the MAF and Intake caused my idle to be at about 800RPM, instead of 400RPM like it was before.
And this is weird.. On some days my mileage would be incredible, both street and highway. The range would drop 1 mile every 2-3 miles and my MPG was great. I believeelieved should have been my true mileage.
But most days it's still a 2 miles loss. My current MPG with the thank is 14 right now and I know I can do better. It feels like I'm only getting half of whatever in the tank that's depressing.
So what should I do? I'm thinking the temperature sensor and 02 sensors should be replaced. But I don't want to take a guess with replacing both of them. May need to change out the sparks again for some proper NGK Irdium IX but I'm still puzzled that I'm getting horrible performance on the copper.
Time to change...you will be pleasantly surprised with results .
Your wiring harmess side connector shell hasp or shell may break or fracture. ...acquite a new connector shell before undertaking the project...the number is stamped on the shell..do not get talked into a splice pigtail...the idividual contacts release with a safety pin and snap lock into the new connector housing.
You will be tempted by aftermarket sensor pricing...
Don't do it.
For best performance, purchase an OEM specific temperature sensor and crush washer from dealer.
Report your results..
Last edited by YODAONE; 09-03-17 at 11:00 PM.
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