Owner needs help.

Hi whunter

Bad MPG 1998 E320 150,000 miles.

I spoke with you a few days back regarding my 98 E320’s poor gas mileage.
I had the car checked for leaks but they did not find any which is good news.
The fuel trims were also checked and they were all within specs.
The last time that I filled up the tank I had added the Chevron Techron fuel system cleaner and today the low fuel level light came on at 360 miles.
I do feel that the exhaust vapors are a bit rich but only sometimes, other times you only feel like clean warm air is pumping out.
Can worn plugs or any bad vacuum lines cause this?

· The fuel filter was replaced @ 143,000m Sep 2009

· The Plugs were replaced @ 93,500m Apr 2005

· The cats were recently cut off and inspected.

· There are no codes on the computer.

What about cleaning air flow sensor.Did my S 320 24 mpg city and hwy mixed.Was 21.Oh yeah mine was rich a little,and I quit using 10% ethonal,now shop for real gasoline.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Spark plug service cycle is 4 years so those are due but I doubt it's your problem.

As mentioned, get some CRC MAF cleaner at Pepboys or other auto parts supply and clean MAF.

You must remove MAF insert to clean. You need a Torx Plus (5 point ) TS45 security bit to remove mtg fasteners. In a pinch, you can grab the edge of the 'washer head' screw with pliers or vicegrips to remove.

You don't say but what is your gas mileage. A lot depends on how you drive. I'm guessing the mixed/city driving is in a range of about 15mpg to 19mpg for most drivers and highway is 23mpg to 30mpg. That would be an average over several tankfuls using the miles on the trip odo divided by gallons pumped.

Another thing to investigate is the O2 sensors which usually start failing at about 100K. There is a procedure for checking the electrical characteristics of the sensor but I don't have it currently. Eventually bad O2 sensors will throw codes.

Finally, have you considered that you just have a worn engine. Most engines can't produce as new mileage as wear takes a toll on compression, injectors, etc.

Good luck.

So, what mpg does the low fuel light coming on @ 360 miles, equate to?

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'06 E320 CDI
'17 Corvette Stingray Vert

16.5 gallon fill up.

Roughly 22 MPG highway.

No city driving.

The owner noted a drastic drop.

I'm getting 25 MPG mostly highway on my 98 E320 with 173k miles. If I am burning gas outside of the Chicago area I can get up to 4 MPG better gas mileage.

Based on the age of the plugs I would replace them or at least pull them and inspect for gap and color. Also check the air filter.

Have the wheel bearings been repacked?

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles

Hi Guys, I just got this link from whunter. I have had this car for about 6~7 years now and it has always given me 400 miles a tank combined. For the past few months I have noticed that the engine is running a bit rough, it feels like there is a misfire but there are no codes! I’m in the process of moving and will be receiving my tools in a couple of weeks. Once I have them I’m planning on doing a compression test and also check the pugs. That should tell ma bit how the engine is doing.

Just yesterday I replaced the fuel filler cap and it looked like there was a leak from the gasket. I will post the results in a week or so when I have to fill up again. I’m also going to be posting a FYI on the fuel filler so in case your cap gets stuck and doesn’t want to come off you know why. It’s a easy DIY that you have to inspect.

Southern, No I haven’t checked the wheel bearings but that’s on my list because of a vibration. Also I’m using a K&N air filter so I’m sure that’s not an issue. I will pull the plugs in a couple of weeks and check.

Skid row, here are my miles for the last 3 fillups.

Drove 309.9m put in 17.182g =18m/g combined
Drove 235.8m put in 13.521g =17.4m/g combined, I also put in Chevron fuel system treatment.
Drove 375.7m put in 19.026g =19.7m/g combined, I think the additive adjusted or corrected the guage.

Richard, I recently had to replace the MAF sensor because I took it out to clean it. Funny you mention the O2 sensor because I have been looking for a “how to” to inspect them. I have purchase the MB Wis from ebay and when I get some free time I’m going to look and see what I need to do.

Thanks for the input guys!

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98 E320 175,600m
99 ML320 175,500m
as of 12/2012

The K&N filter oil is known to wreck mass airflow sensors on Mercedes...

If the K&N air filter is the reusable one, I believe that IS your problem. The oil off the filter media, fouls the MAF sensor which results in 2-3 mpg loss. It happens pretty suddenly and stops pretty suddenly when you clean the MAF and put a paper filter back in.

If the MAF is failing (voltage out of range) you usually get P0170 and P0173 OBD codes. But if it's fouled no codes just lower gas mileage.

I put the K&N on when I got the car about 6 years ago, I’ve never put the oil on it. All this has started within the last 4 months or so.

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98 E320 175,600m
99 ML320 175,500m
as of 12/2012

K&N filter topic links thread
http://www.peachparts.com/shopforum/showthread.php?p=1354738



4. How often do I need to clean my K&N air filter?
http://www.knfilters.com/faq.htm#4

K&N Air Filter Cleaning Instructions
http://www.knfilters.com/cleaning.htm

im only getting 22 mpg highway in my E320 cabriolet and thats driving at speed limit!

and thats with consistent 14 gallon fill ups because thats what the tank will take in the cabrio

k so what about the crappy mpg's? I've got a MANN filter.. new

I would suggest looking at the mixture adaptation numbers.
Ideally they sould be very close to 1.00.
If they have gone to 1.25 or are heading in that direction replacing the MAF will usually cure the problem.
MAFs (mass air flow sensors) are common issues, and may be defective without a CEL.



Possible:
* Bad spark plugs.
* Bad MAF.
* Bad O2 sensor.
* Tired engine.

So how can I find out what the mixture adaptation numbers are?

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98 E320 175,600m
99 ML320 175,500m
as of 12/2012