Ok... So here's the deal... I just bought this '02 CL-S Auto w/ 74k on it. CLEAN as can be. I knew that I wasn't going to be getting the same mileage as my civic (32-38mpg) but I was hoping for at least 20. And so far it has gone something like this:
First tank: 17.4mpg
2nd tank (new plugs/air filter/cleaned EGR): 18.18mpg
3rd tank (raced it twice against my buddy's S60R and won 2x): 15.4mpg
and this last tank was 17.8mpg

I rarely go over 2500-3000 rpm driving daily in city & some interstate. I can't figure this out as my brother's Suburban is getting 17mpg and I'm driving a HONDA!!!

I'm ordering NUMEROUS parts (Coil Overs, Wheels, Intake & TB Spacer, Pulleys, Headers, A "fat-cat" and custom exhaust) but if I can't get more mileage out of this now, I think there may be more serious issues than originally expected and don't want to dump a crap ton of money into it. Any ideas? I can't even find a part number for the fuel filter either?

 

I get 15.9 city mpg w my new 4600 lb MDX.
I can get less if I drive it hard and fast or use less than 50 - 50 plus - premium mix.
At 74K ... check how dirty intake system, & valves are.
I had a sandblast clean done on my '02 Jeep at 60 K and got another mile per gallon.
I think this meth/eth they put in really fowls it up.
But note your range of repeatablity seems weird.
You might want to check the repeatabilty of your odometer ... its prob not accurate either - see my post and link in mdx section.

 

I only run Premium 92 - no ethonal

 

I dont know what state you are in but most states use like 10 - 15 % meth eth in their winter mix at pump.
Prem is suppose to be 93/94 octane. Plus is 89/90 and reg is 86/87.

 

Nebraska - 89 has 10% ethanol, but I run th 92 Octane that is not mixed. Regular being 87. I haven't run the race fuel yet (99 octane) but that will wait til the summer trip KCIR.

 

You need to check it more ...
The truth is you dont know what is in the tanks {could be Kat urine}.
There is no 92 octane premium anywhere in the US
and all winter mixes are less w alch eth or meth.
You will get better w summer mixes and if you read whats
posted on the pump you are naive.
Extra octane is wasted octane !!

 

Premium is actually 91 octane or better.

How do you know its not mixed? Does the sign specifically say only regular unleaded is mixed?

92 octane exists. Numerous stations in my area sell it.

OP - Check the catalytic converter. Do an oil change. Its possible the valves are out of spec too. What brand fuel are you running? How noisy is the engine at idle? What plugs did you buy? Whats the condition of the O2 sensor? If possible, try to get your AFR values.

Point blank, your mileage sucks. If you are truly driving it easy and getting less the 20mpgs, something is clearly wrong. I have a built motor and when I beat the crap out of it I cant get anything lower then 22mpgs.

 

Drive slower on the freeway. I drive 60 mph and get about 23 mixed. I also have intake, headers and exhaust so that helps but the biggest deal is highway speed and city driving.

 

While speed does help, I drive 65-80 on the highways, and the 6MTs rev higher then the 5AT.

 

In the city i got 16-18 mpg thats normal i just dont care about it anymore. 24-26 hwy depends on how i drive. But i wish i could see 20-22 in city and 28-30 on hwy.

 

I'll have to take a picture:
87 Regular Unleaded
89 w/10% Ethanol
92(sometimes 91) Premium Unleaded

I was saying regular & premium aren't mixed with Ethanol

• Cat was replaced 10k ago (per paperwork that came with the car)
• oil changed when I bought the car with Mobil 1 5w-20
• I use 1 of 2 gas stations (QT- Guaranteed Gasoline or BP/Amoco)
• engine is very quiet at idle- basically can't even tell it's running sometimes., NGK Iridium IX 6441 Plugs
• O2 sensors were replaced when I bought it as a "just in case" situation.

any other ideas?

 

What brand of O2 sensor ?

 

yes there is 92 octane

 

Bosch, but I don't have the model numbers on me. No check engine lights though.

 

Our ECU dont like Bosch O2 sensor but im not sure if that possible.

 

Ditto.

Get a Denso sensor. Im surprised you havent thrown a CEL yet.

 

I used to be the kind of person that believed that all brands of gas are the same as long as you are using the same octane until I switched to Shell. Prior to using shell I used to get 16-18 miles per gallon city driving and since I get 20-23 city driving also my car feels more power. I'm not saying that Shell is the only gas that will do this but it does point out that not all gas is created equal.

 

^I have to agree i always used exxon because was the nearest one but then i switched to shell and everytime i use it i get like 20-30 miles more from a tank.

 

I'm still waiting on more tune up type parts, but did find out that the original tank had 89+10% ethanol mix from the dealer and think there is still some of this mixed into the tank as I'm only running it down to 1/3 tank before refilling. I'm going to run this tank bone dry and fill up on some good gas.

 

Not me I find that going to Chevron or shell I was only getting 240 to a tank, now that I'm going to Costco, Sams clubs I'm getting 250-260 a tank, sometimes I get 245 but thats when I push it, but I still need to do an Oil Change Air filter Spark plugs and work on my solenoid

 

That is totally contrary to what I found. I went to Costco for several months and my car lost power it was really noticeable when I stopped going there this issue went away. I can't comment on Sams club though.

 

we used to get fuel at Sam's club but when our membership expired last month we decided to go to Cosco. We find no difference.

 

Every Costco gets its fuel from different suppliers. Luckily, the Costco I go to gets good gas.

 

Turns out, it was the injectors. I pulled them over the weekend and had my brother (the technician) test them and they weren't "misting" but were "squirting". He tried to clean them, but unfortunately, it was a lost cause. Bought new ones and installed them. Put 170 miles on it over the weekend and not even to a half tank yet. I think the gas mileage will finally be where it should be.

 

24 mpg... seems to be fixed!

 

How many miles on car ?

Edit: 74k and already bad injectors ? Weird isnt ?

 

It is odd, but I think the previous owner may have not been using very good gas. We did a leak down test and compression test and everything checked out, so there isn't any damage noticeable without taking apart the engine. The fuel system just needed to be cleaned out. The injectors were sticking and were primarily "dirty" rather than faulty.

 

thats good I should inspect mine then 171 and not @ half a tank yet..

 

So injector cleaner didnt help ? You bought a set of new ones or just one ? No matter how easy im on the gas cant get more than 140miles on first half of the tank. Sometimes less. I drive mostly in the city

 

After my valve adjustment 2 months ago, I am getting roughly 340 city miles per tank, and just this past weekend I took a roadtrip to Daytona...Halfway on the fuel gauge my trip odometer read 212, so thats roughly 425 highway miles per tank.

I have Intake and headers.

 

The injector cleaner helped for about 1mpg, but that's just not enough. I replaced 4 injectors. Looks like 2 were previously replaced. The signal to all 6 was checked to make sure there wasn't a bigger problem and they're good to go. It was an expensive weekend. I will probably be getting a valve adjustment when I get all the other new stuff.... cams, cam gears, pulleys, exhaust, t-belt, water pump, etc etc

 

btw - that's only about 25mpg if you go through the full tank for 425

 

Another reason to use top tier gas and regular fuel system treatments or seafoam.

I'm sure everyone's injectors arent in tip top shape especially with CLs now reaching 100k+ miles compared to new injectors.

 

Any DIY on checking the injectors ?

 

<---Winner:



No top offs, odometer was reset at fillup. That was a trip from VA to NY last summer and the a/c was on the entire way. IIRC it was about 280miles at the half way mark.

 

thats good..

and Gary that top tier gas stuff is BS like I said I get better MPG at Sams club then I did at Chevron and shell

 

W t f ? Best i got lately was about 25mpg on the way to great falls meet 5 weeks ago. It was like 220miles on the tank

 

No DIY, my brother handles all the tech stuff like that. The dealership has access to runners and signal relays to run the injectors outside the car. I'm a desk jockey, my brother is the technician.

 

I'm going to try to pull mine out and look at them hopefully it isnt to hard

 

Just looking at them isn't going to tell you much. I couldn't tell the difference between the bad ones and the good ones when my brother had them out.