rommelle63

Hi everyone,

my car is getting really poor mileage, the onboard computer never show more than about 15 mpg, even on highway. not running super smooth at idle, i use 93 octane gas. looking for input as to what i could try doing myself with going to stealership...

Thanks

boardboy330

You could clean the EGR - a clogged tube would cause the issue you are describing. Dirty injectors would also cause it, as would a dirty fuel filter. I would start with the EGR though.

Not sure about the E - but it's a free DIY on these motors.

rommelle63

what is egr and where is it? and how do i clean it

AMGAffalterbach

Try checking the fuel and air filters as well. Make sure the engine can breathe and sip properly.

rommelle63

thanks to all who made suggestions, i amtrying to figure out where this EGR is... and also looking for suggestion on what solution to use for injector cleaner, agin thanks for your help. and if any of you have any tips in general abouts this vehicle would be appreciated, I've been reading some what negative comments on these vehicles from 03 and newer

AMGAffalterbach

Usually it's the earlier W211s before facelift that have issues. Check the forum and the stickeys up at the top some of those threads may apply to you. Personally, this car - while expensive to maintain - has been very problem free even driving a LOT and very spirited as I do. I can get up to 27 MPG on the highway cruising at a constant 75-80mph and I have the V8 model. So I would check one of the usual suspects such as EGR or filters. 15 mpg max (unless you're using poor quality fuel which you are not I suspect) is not normal.

rommelle63

thanks AMGAFFALTERBACK, i will try air and fuel filter, and see what happens, thanks alot for your input... if you're getting that kind of mileage with a v8, i should be up there also. still learning to navigate on site. it's good to know that you haven't had any major issues with same style vehicle, even though you drive the v8, and i only use 93 octane

vettdvr

Plugged cat converter

otto6457

Plugged EGR valve will not cause poor fuel economy and would set a code within two trips. Plugged injectors will cause a miss on a particular cylinder or cylinders and will set a misfire code and an MIL light. It would be worse than a "not smooth idle" It would be quite apparent that you had a miss. A dirty fuel filter will lead to a lean condition. A lean condition can cause poor idle quality, but will also be exhibited in poor acceleration, especially at high rpm. Lean condition will only affect fuel mileage adversely when missing occurs. Spiky injectors (injectors that have a partial blockage of the pentels due to carbon buildup, will cause a lean condition as the fuel is not properly atomized into a fine mist, but is instead emitted as larger streams that stick to the intake runners and valves) can cause a poor idle and reduced performance. And can cause the engine ECU to see a lean combustion chemistry and attempt to rich-en up the mixture, which can affect over all mileage. However, spiky injectors will also often cause a poor starting complaint. Especially in cold weather. Vettdvr is correct about the cat converter also. But, you should see a greatly reduced performance at high RPM.

There are many variables that can cause poor fuel economy, but few that won't set a MIL light. Such things as variable valve timing and intake air management can cause poor fuel economy but will result in codes and an MIL light.

A few simple ones that won't set a MIL light are:

Dirty air filter
Tires under inflated
stuck fuel pressure regulator
catalytic converters partially plugged
sluggish A/F sensors. (not completely bad, but reacting very slowly)

Since you didn't mention how many miles your car has or what engine you have it's even harder to make a guess.

To actually diagnose poor fuel mileage we need to see the short and long fuel trim numbers, A/F sensor activity, and ignition function. This requires a scan tool and the knowledge to know what good numbers and bad numbers are, and what causes good and bad numbers.

Anything else is pure guess work and is just throwing money at a problem and hoping you get lucky.

rommelle63

i have the 3.2 and it has about 111k,thanks for the input

otto6457

One other important point.

If you're going to accurately check your fuel mileage you need to make sure that you use the same gas station, same pump, and at as close to the same temperature as your last fill up. Do NOT top off the tank. Allow the pump to shut off on it's own then remove the nozzle. Also, fill up on a middle or low notch on the pump handle. Not the fastest notch. The pump will more accurately read the fill pressure on a slower fill rate and stop at a more consistent rate.

The fill rates and pressure sensors vary considerably between stations and even pumps at each station. You need to be as consistent as possible when re-filling or you're figures are useless.

Bad data in....bad data out.

In addition, high alcohol percentage in your fuel will reduce fuel mileage. Alcohol does not have the same energy coefficient as gasoline. It takes more alcohol to make the same energy output.

rommelle63

yes, I use the sexact same pump facing same direction and within an hour of each other,as far as the pump handle i will also do that . i use the onboard computer to look at mileage, and i also do the math, miles traveled divided by gallons, thanks very much for the info. So glad i found out about this site, everyone has been great, thanks a millioon

rommelle63

and as far as the ethanol it's 10% and i can't find a station without the ethanol, thanks big brother for screwing with us...

lglitt

I have a 2008 E300 (Canada only) and have just replaced the Magnetic Camshaft Adjusters. Since then I have experienced a 20% DECREASE in fuel economy. The mechanics don't have a answer and say that if one of the MCA's were faulty the code would appear - I agree. Any suggestions? The car has high miles (175,000kms) but has been regularly serviced at the stealership since new. It sucks because now my BMW 530XIT gets much better mileage than the MB!
Thanks

Larry (from snowy Calgary)