Very Bad Gas Mileage :(

[Bali26]

Hi,

I'm only getting 10 miles a gallon city and 15 miles a gallon highway. This with me very light on the pedal. This problem is taking all the fun out of having a LS400.

There are no warning lights (except the TRAC which comes on sometimes after 5 mins of driving).

38 psi tire pressure.

No smoke or strange sounds or vibrations.

No obvious vacume leaks.

Now I've heard of sticking calipers. How do i check for it?

Any other things I can check for? I cant afford taking my car to a mechanic right now. I have most tools.

Any and all suggestions are very very appreciated.... Thanks in advance

[Jerry Bransford]

Have you ever replaced your 02 sensors? By now, the 02 sensors in a '91 anything would be toast and in need of replacement. The upstream (nearest the exhaust manifolds) 02 sensors are what measure the air-fuel mixture and tell the computer how to adjust it. When they go bad, they tell the computer the air-fuel mixture is too lean which causes the computer to set the mixture more rich than it should be... which ruins the mpg and performance.

[Bali26]

Thanks Jerry,

But wouldn't I have a Check Engine light if that was the case? Is it a DIY?

Cheers

[cardona6569]

Have cleaned, replaced the air filter, throttle body, maf sensor? Also have you changed the spark plugs, cables, rotors?

CPR

[Jerry Bransford]

But wouldn't I have a Check Engine light if that was the case? Is it a DIY?

Cheers

Not necessarily on the Check Engine light. Changing an 02 sensor is just like changing a spark plug, though I haven't done it on either of my two Lexuses to know if there is anything in the way of getting to them that could turn a fast easy job into a more time-consuming job. It's an easy ten minute job on my other cars and Jeep. They're screwed into the exhaust system, usually just below the exhaust headers. An 02 sensor even kind of looks like a spark plug with a single electrical connector and plug coming out of it. :)

[SimonR]

Hello. New guy from England here. I had a similar-sounding problem and it was because of a seized piston in the front passenger-side caliper.

14mm sockets to remove the caliper. It was obvious which piston had seized as it wouldn't move while the other would. I also noticed uneven pad wear for that piston. Short term fix is a g-clamp or similar to just to get the piston moving. Proper fix is to get the caliper seal kit from Lexus and replace. While the pistons are out (use brake pressure to remove them) you will see where it has been sticking. I used fine grade paper to remove corrosion (water in the brake fluid). Seal kit comes with the correct grease.

Very easy to do and no specialist tools required, but some are concerned about the safety aspects of messing with the brakes. That's up to you.

[Bali26]

Thanks a lot for that Simon,

How did you know it was sticking? Did you just move it by hand to feel it? Do the pistons just come out completely? And brake fluid leaks out?

Thanks

Im also gonna buy a multimeter and check O sensors and MAF

[pishta]

Thanks a lot for that Simon,

How did you know it was sticking? Did you just move it by hand to feel it? Do the pistons just come out completely? And brake fluid leaks out?

Thanks

Im also gonna buy a multimeter and check O sensors and MAF

Just feel your rims after a drive, the sticking caliper will heat up your rotor something fierce and itll go straight to your rim. One will be way hotter than the other.

[aarman4]

Thanks a lot for that Simon,

How did you know it was sticking? Did you just move it by hand to feel it? Do the pistons just come out completely? And brake fluid leaks out?

Thanks

Im also gonna buy a multimeter and check O sensors and MAF

Just feel your rims after a drive, the sticking caliper will heat up your rotor something fierce and itll go straight to your rim. One will be way hotter than the other.

Take a look at this, and always check this whole site for anything relating to your car, it's a goldmine!

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

I have new O2 sensors going in once some house chores are finished... I have pulled them previously and it is pretty easy. As far as the CHECK ENGINE LIGHT, I found that my light was actually burnt out on my speedo bezel that projects the warnings down to the guages... The LEXLS site shows how to replace this (speedo/guage section). The little lights may be tought to find (i got a whoe new bezel loaded with lights for $10 on ebay, a steal), but you may want to try moving a working but non-essential light to the CEL position. I used the seatbelt light for the time being and tried it in there to see a CEL and engine codes for O2 sensors...

Best of luck!

BTW - In Canada, O2 sensors were $100 at the store for universal, and almost $300 for OEM from NAPA, but I found both on Ebay for under $30, might be worth checking out if this is your problem.