MPG gauge for 1991 Lexus LS400?

[Titanium]

I am interested in buying a MPG gauge for my 1991 Lexus LS400 if there is one currently made that will work with this car?

I bought this car over two years ago with 160,000 miles on it and now I have 212,000 miles on it. I maintain this car better than the factory manual suggests also. My work commute is 80% Highway. The LS400 has a drag coefficient around 0.29. The smooth running V8 in the car hits around 2,400 RPM at 60 mph and around 2,800 RPM at 80 MPH. I am getting around 21 MPG in this car average, but I drive it at 80 MPH on the Highway.

This car did start getting worse than normal gas milage this summer. I read the main gas milage killer in these cars can be the engine block coolant temperature sensor, so I replaced that sensor with a factory Lexus sensor. I gave the car a complete tune up with new Lexus spark plugs, new air filter and cleaned out the throttle body. I also switched to using ethanol free gas. 90% of the gas available in my state has ethanol in it, but there are a few stations that carry the ethanol free. All of this did improve the MPG with this car. I recently just put in Chevron Techron fuel system cleaner in the gas tank. I also bought some Red line SL1 fuel system cleaner that I will use later. I read there is a higher concentration of the chemical in the Red Line brand vs the Chevron that really cleans your fuel system on the bob is the oil guy forums. I used to only use Chevron high octane gas with ethanol and Techron in it, but since the switch to ethanol free no name gas I decided to add fuel cleaners to the fuel in my car just as preventative maintenance.

I am wanting to use a MPG gauge on this car and slow it down around 65 MPG on the highway and try to get well over 25 MPG with this car.

I bought the Lexus after I sold my 1997 Honda Civic HX that had almost 300,000 miles on it. I sold the HX due to it needed quite a bit of money put into it to go another 100K miles. The Civic HX is a fantastic car.

[MetroMPG]

I'm surprised the LS doesn't have a factory MPG gauge!

I thought most luxo-barges had them back then, meanwhile the MPG-focused economy cars didn't. (Oh, Irony!)

Regardless, since it's pre-OBD-II and the usual options (eg. ScanGauge) won't work, you'll need a DIY MPGuino. You tap into 12v power, vehicle speed sensor, and one fuel injector signal and you'll have a very accurate gauge with useful features.

FYI: I put one in my '90 Miata this summer:

http://ecomodder.com/forum/showthrea...vss-35550.html

Look for more info in the MPGuino sub-forum.

[spacemanspif]

Don't forget the usefulness of a vacuum gauge.

Switching to no name gas with additives won't offset buying brand name gas if you are using the additives on the regular.

[Ecky]

Does the LS400 call for high octane fuel? Be aware that higher octane gas has marginally less energy per gallon, so all else being equal, your fuel economy will be slightly worse. Many newer vehicles can advance the timing a bit and (partly) offset the extra fuel costs with higher octane gas, but it's almost never cost effective.

To answer your question though, the device you're looking for is the "MPGuino". There's a subforum dedicated to it here in the instrumentation section.

[MetroMPG]

Originally Posted by Ecky

Does the LS400 call for high octane fuel? Be aware that higher octane gas has marginally less energy per gallon,

Really? Learned something new today!

all else being equal, your fuel economy will be slightly worse. Many newer vehicles can advance the timing a bit and (partly) offset the extra fuel costs with higher octane gas, but it's almost never cost effective.

The timing advance wouldn't offset the lower BTUs to at least cancel out the efficiency difference? (Disregarding price issues.)

[Ecky]

I remember reading a study that had been done, but couldn't find it when I looked. As I remember though, the timing advance didn't offset the price difference. It was measurably positive in some of Ford's Ecoboost engines (high compression turbo), but even in most vehicles which could advance timing significantly (usually high performance engines), the fuel economy difference was negligible - neither better, nor worse - and it costs more.

[Titanium]

Originally Posted by MetroMPG

I'm surprised the LS doesn't have a factory MPG gauge!

I thought most luxo-barges had them back then, meanwhile the MPG-focused economy cars didn't. (Oh, Irony!)

Regardless, since it's pre-OBD-II and the usual options (eg. ScanGauge) won't work, you'll need a DIY MPGuino. You tap into 12v power, vehicle speed sensor, and one fuel injector signal and you'll have a very accurate gauge with useful features.

FYI: I put one in my '90 Miata this summer:

http://ecomodder.com/forum/showthrea...vss-35550.html



Look for more info in the MPGuino sub-forum.

This 1991 LS400 does not have a MPG gauge. My friends Lexus that is 12 years newer has one though. I do not know what the first model and year of Lexus was that came with a MPG gauge.

It is good to have the MPGuino option. Thanks

[Titanium]

Originally Posted by spacemanspif

Don't forget the usefulness of a vacuum gauge.

Switching to no name gas with additives won't offset buying brand name gas if you are using the additives on the regular.

Every car I have owned got noticeably worse MPG using gas with ethanol in it. That is the main reason I have recently switched. I live in Utah where most of the gas sold at the gas stations here contain ethanol in it. However ethanol free 88 octane gas is available at a very limited few gas stations here. I started using it in this Lexus LS 400 that I have.

I plan on adding the fuel system cleaner once in awhile. Not necessarily to every tank.

[Ecky]

I've tried both in cars I've owned and the difference disappears into background noise. On paper, there's an approximately 5% BTU difference, which should work out to exactly 1mpg in a 20mpg vehicle.

[Titanium]

Originally Posted by Ecky

Does the LS400 call for high octane fuel? Be aware that higher octane gas has marginally less energy per gallon, so all else being equal, your fuel economy will be slightly worse. Many newer vehicles can advance the timing a bit and (partly) offset the extra fuel costs with higher octane gas, but it's almost never cost effective.

To answer your question though, the device you're looking for is the "MPGuino". There's a subforum dedicated to it here in the instrumentation section.

I have always ran this Lexus on 91 octane which the owners manual says to use in it. I did find 91 octane ethanol free gas and used it once, but they charged almost $4.00 a gallon for it here. I found 88 octane ethanol free for under $3.00 a gallon and have been using that for two months. My car runs great on the 88 octane ethanol free.

This car is rated at 21 MPG on the highway from the U.S. Department of Energy fuel economy.gov website. I am getting 21 MPG overall with my long 80 MPH highway commute. Slowing the car down to around 65 MPH using a MPGuino should result in better than that.

I used to get 38 MPG on this same exact commute in my Honda Civic HX driving it 75 - 80 MPH on the highway. 50% of the cars on the freeway are now doing 75 MPH or faster here in Utah. The I-15 posted speed limit where I normally drive is 70 MPH. People are driving faster here in the last year on the highways than I have ever seen except for stop and go rush hour traffic which is also far more stop and go this year due to far more cars on the road now than ever before. I generally drive with the flow of traffic in the fast lane or the lane to the right of the fast lane which really is around 80 MPH.