Poor gas mileage

[junklar]

Why am I getting poor gas mileage? I recently changed my O2 sensor (after catalyst) since the check engine light was on because of this, but that did not help either. I'm getting around 14 mpg city and highway combined.

Please help me out.

[Espresso]

Fuel filter? Air filter?
Did this come on suddenly, or was it gradual?

[junklar]

I've had this ever problem since I bought the car. I bought it around 108k, and now it has 111k.

It also starts hard on a cold start, which from what I read on a different thread started by NEA, leads me to believe that the fuel injectors needs to be changed. Would this make a big difference on the mpg?

Air filter looks fine, but I don't know about the fuel filter. Is there a way of checking this?

The problems seem to come one after another. I replaced the head gaskets, the wiring harness, the alternator. I'm going to replace the throttle actuator soon, and then maybe the fuel injectors. I'm not including the things I fixed by myself. I still have a vacuum leak (the buzzing sound), which I stopped temporarily by sacrificing the center vents.

[1995c280]

you live in nyc guy.....its winter time. just change your fuel filter and spark plugs. stop flooring the car, HAHA. and make sure you are using the correct weight oil in the engine and check your battery. i get only about 280-300 miles on a tank it CT during the winter (city/highway combined).

Jason

[junklar]

I wish it was that much.. I get about 225 miles.. I thought the tank was 16.4 gallons? I see people on here getting 300 - 350mpg. It's really annoying..

I'll change the throttle actuator then start throwing parts at the car. I can't even kickdown anymore... I think the battery might be next after that.

So, in total with the throttle actuator repair, the car's total damage is going to be around $7k.

Jason, did you have the vacuum leak as well? Did you repair yours?

[Len013091]

I usually run about 280 miles tank, with my normal driving(spirited), however, I did manage 350ish once when I tried. I get about 32 on the highway, not sure what the city average is for me.

[Nelson Lago]

It’s a 16 gallon tank and Im getting probly around 14mpg too and take in to consideration that the Mercedes 6cycl arent very fuel efficient

[1995c280]

no i have no vacuum leaks!!!!!!

[99C280Sport]

My last fill up I drove about 360 miles and put 15.4 gallons in the tank. That was 75% highway miles.

I think the worst I've ever gotten was like 19.8 mpg and that was 90% city miles.

[junklar]

Nelson, does your car also have a hard start?

It's as if I'm driving a S-class with this mpg

[Nelson Lago]

It does start a little hard when its cold but notthing to worry about but when i first got the car my mpgs were maby 18/19 mpg but now worse i just thimk i need new plugs and wires

[anf6789]

my 1994 c280 gets about 17-20 mpg, it starts up fine/runs fine. i get about 250-300 on a tank of 93octane, it sucks,lol

[xvvvz]

>>It also starts hard on a cold start, which from what I read on a different thread started by NEA, leads me to believe that the fuel injectors needs to be changed. <<

Do you still have the original fuel pressure regulator? If so, you might want investigate that. I have seen threads about bad fuel regulators causing hard starts.

>>I still have a vacuum leak (the buzzing sound), which I stopped temporarily by sacrificing the center vents.<<

Can you expand more on this please? The problem/cause and what you did to fix it?

Thanks.

[junklar]

I think it is the original fuel pressure regulator.. the previous owner refused to do any kind of maintenance..

were the threads you mentioned on club202 or on another forum? If you have a link can you please send it to me I'd like to read up on this.. I think it'll be much cheaper to replace the fuel pressure regulator instead of the fuel injectors..

zadefaraj had a nice thread and diy of fixing the vacuum leak which causes the buzzing noise that comes from the trunk.. it involves taking the dashboard apart.. I don't plan on fixing it yet, so I temporarily fixed it..

When you open up the hood on the left side you should see vacuum lines right where the hinges of the hood is.. about 6-7 of them.. I took out the green line, which is on the top row and all the way to the right (when looking at the lines from the passenger side of the car)

The center vents no longer blow any air at all, but it's better than having that annoying buzzing sound coming from the trunk.


xvvvz do you have a vacuum leak as well?

[junklar]

i use regular.. trying to save at the pump

[aruba]

ok well guys i had kind a like the same problem all of a sudden the car started to run a bit richer and starts in the morning would be a bit hard. turns out it was the mas air sensor you could have youre lokal mb dealer check it for you on the star diagnosis. hope this helps

[xvvvz]

>>were the threads you mentioned on club202 or on another forum?<<

There are lots of posts in regard to the fuel pressure regulator here on club202. Just use the search button. I cannot remember if the particular thread which talks about how a number of regulators are failing was here or on another forum. Also, do a search on cold start. You will probably find a number of threads on that topic which talk about the many things people have tried.

Re: buzzing - Ok, I thought you had a buzzing sound in the dash or engine compartment itself versus a buzzing in the trunk that was caused by a problem in the dash/engine compartment :) I know the sound of the air pump buzzing in the trunk and fortunately I am not hearing that at this moment.

I thought I had read you were replacing your throttlebody, so I thought maybe this buzzing was related. These can buzz when the engine isn't running but the key is turned to the on position.

[chaddeus]

Originally posted by junklar
i use regular.. trying to save at the pump

Among other reasons, the wrong octane may cause gas mileage to decrease. Something about the timing being retarded to prevent pinging. Someone correct me if I'm wrong.

In short, get your car running on the recommended octane before trying to accurately diagnose fuel economy issues.

[omeyhomey]

Here are a few good inexpensive tricks.

Run a full can of seafoam in a half tank of gas and drive the car aggressively for the rest of the tank, This will clean out the entire fuel system including fuel filter, pumps, fuel rails & injectors. Don't confuse this with normal injector cleaner which is basically gimic crap by comparison.

Furthermore, changing both engine & differential oil to royal purple can seriously increase gas mileage a drastic amount b/c of Royal Purples special synerlec formula (which no other oil has).

Intake and exhaust will also help with fuel mileage by leaning up the mixture. These cars normally run pretty rich in stock form so anything you can do to improve that is always helpful.

And of course the best think you can do is reduce weight, weight is an enemy of fuel consumption as well as acceleration, braking, handling and etc.

Also other modifications as well will increase gas mileage like performance pulleys, or any other modification that will increase efficiency and reduce drag on the engine. Using less A/C and removing engine fan and switching to electric can also help.

One thing that will DIRECTLY DECREASE fuel consumption is injectors, avoid upgrading injectors at all costs unless its absolutely necessarily (which for M104s isn't unless you go forced induction). More weight (via subwoofer systems as well as other crap will of course indirectly reduce your gas mileage as well. (remember weight is your enemy).

You can easily increase your MPG by roughly 5mpg if not more just using the tips above, in the long run it will save alot more $$ as well.

[junklar]

aruba - "you could have youre local mb dealer check it for you on the star diagnosis"

Would the MAS failure come up on a on board diagnosis scan?

Those that have had a bad MAS, did the check engine come up on your cars?



xvvvz - "I thought I had read you were replacing your throttlebody, so I thought maybe this buzzing was related. These can buzz when the engine isn't running but the key is turned to the on position."

I have that buzzing too lol.. I didn't have this buzzing from the throttle body for a couple of days, but today I heard it again. I can still hear it when the engine is on as well.



omeyhomey - "Run a full can of seafoam in a half tank of gas"

I'll definitely give this a shot.. I hope they sell it at the strauss-store

Thanks for the replies...

[aruba]

yes it comes in in the star diagnosis you will have to look in the me ( motor electronics) actual values of the car . the mas sensor should read between 14 to 20 cfa if it reads less like 12 then youre mas is not working properly youre mb tech should know about this

[travisC220]

I use regular also, dealer says it's ok to regular in 'em, just don't go switching back and forth from Premium.

[travisC220]

I usually get 450 miles out of a tank, about 90% highway driving. I've got the four banger in my '96 C220.

[junklar]

Originally posted by travisC220
I use regular also, dealer says it's ok to regular in 'em, just don't go switching back and forth from Premium.

Do you have a knocking sound coming from the engine when the car isnt warmed up?

[timmyj51]

Originally posted by travisC220
I use regular also, dealer says it's ok to regular in 'em, just don't go switching back and forth from Premium.





Must be settin' you up for the $$$ he's gonna make off you
for that valve job. Wouldn't even
THINK of using anything except premium in my MB. Heck, where
I am it's only about 12 cents more per gallon than regular.
Not gonna put my car in jeopardy just a save a few cents
per fillup.

[Sulaco]

Agreed on the regular vs premium. Once Shell V-Power hit the market, my entire family refuses to use anything else.

I once was nearly empty a few weeks back and had to stop at a local dodge-store gas station. Their premium was 91 octane, and the station itself looked really pathetic.

Burning that 10-dollars of shitty gas was a nightmare. It had trouble starting, had trouble idling, and had trouble accelerating. Also, that quarter-tank burned extremely quickly.

Filled back up with V-power 93-octane = fixed.

With over 200k miles I still get around 26city/30hwy.

Edit: most I ever got out of a tank was 426 miles. I average between 325-375. And I drive hard.

[omeyhomey]

Originally posted by travisC220
I usually get 450 miles out of a tank, about 90% highway driving. I've got the four banger in my '96 C220.

whats that equate to in MPG? Also whats the official size of the gas tank as stated in the manual?

[junklar]

Hey omeyhomey,

Thank you very much for the seafoam tip .. the car starts like a champ now everytime

the hard start was pissing me off.. embarrassing too

i just saved a bunch of money on car repairs thanks to omeyhomey

Thank you thank you thank you

[omeyhomey]

Originally posted by junklar
Hey omeyhomey,

Thank you very much for the seafoam tip .. the car starts like a champ now everytime

the hard start was pissing me off.. embarrassing too

i just saved a bunch of money on car repairs thanks to omeyhomey

Thank you thank you thank you

:) , its what I'm here for, just doing my part for the W202 community

[DynoXG]

Nice tip Omey.