rennwerkes

Have been getting poor gas mileage for some time.
Have replaced the following:
Air filter
plugs
Clean MAF
O2 sensors
Car has about 90k on it.
Getting 15mpg on about 75% highway driving.
Anything I'm missing or might help?
The only other things I can think of is the MAF, wires, and coils.
Thanks

rennwerkes

Anyone?

MB-Dude

Has your MPG been dropping steadily over time? Or was there a sudden change? The former suggests normal wear and tear while the latter suggests equipment degradation. Depending on highway speed, 15 MPG is not unreasonable for your (I'm assuming) '02 SL.
Cheers,
Jeff

rennwerkes

Jeff,
Thanks for the reply.
I think it happened over time so like you said probably wear and tear.
But I'm wondering if there's anything else that I can change that could help get me a bit better mileage?
Dean

cliffyk

What sort of fuel are you running/do you have to buy in Hawaii?

Octane, %ethanol, has it changed over this same time?

rennwerkes

We have the stupid law that requires 10% (I think) ethanol.
Believe it or not I believe that law was just changed so ethanol is no longer required but probably happens after July 1.
I usually use Chevron premium gas.

MB-Dude

Out of curiosity, what's your average city/stop-n-go MPG? Any correlation?
Cheers,
Jeff

cliffyk

I get 15-19 in "town" and heavier suburban driving (I do do cities), 19 to 21 overall (I live 12 miles from anywhere), and 23 to 24+ or so between pit stops on the Interstate.

rennwerkes

Currently about 10-12mpg

rennwerkes

That's why it's bugging me that I'm getting only 15mpg or less in town/hwy driving.

SRHsl600

With your stable of vehicles, it sounds like you hope the R129 is your economy mileage toy!?! My experience with SL500 and Sl600 is mileage for extended cruise control I 70 back from Denver ( down hill ) they both will be in the 18-20mpg. when in town, stop and go with only a few highway miles 12-16mpg. I drive with energy! be it the 993, or Avalon I hope just to make it to the next gas station!

cliffyk

How are you measuring mpg?

I ask because many do not realise the in-dash fuel consumption gauge (FCG) provides instantaneous fuel consumption feedback. It is very accurate information as it is based on vehicle speed and a variable frequency fuel consumption pulse signal from the EFI system (one pulse = 0.2 l/h consumption)--however attempting to interpret overall fuel use from it, even during a single run of similar conditions, it a fool's errand.

A fellow had once put forth that he got 28+ mph on the highway because he saw the FCG indicate same at some point on a trip. The r129 is a 4300 lb behemoth with a largish engine and a slushbox, designed in the grandest "panzer wagon" tradition.

Fuel economy is not its forté and I suspect was not a major consideration for the original purchasers who plunked down $100k to buy one...

rennwerkes

LOL!
No, I'm not unrealistic.
I know the SL doesn't get great MPG but thought it should get a bit better than what I'm getting now.
Maybe I'll just try swapping out the MAF and see if that helps a bit.
Thanks

rennwerkes

I calculate using the amount of gas filled up and miles traveled.

MB-Dude

Do you feel as if the power of the engine has dropped off, even a small bit? I ask because when I first got my V12, I was amazed by the power. After a couple months, the CEL illuminated and it turned out to be a restricted Cat. Somehow, the honeycomb inside began disintegrating and thus blocking the exhaust. Finally became bad enough for the ECU to register a problem. But once the Cat was replaced - holy smokes - that V12 took off like a rocket. And the MPG rose. Maybe you are experiencing a similar effect.
Cheers,
Jeff

rennwerkes

Hmmm...No CEL but I haven't noticed a drop off in power either.
But bad cats are definitely a possibility.
In fact, here in Hawaii we can remove them all!!! LOL!
Seriously, I've thought about removing the secondary cats since they really don't do much.