CDP

I'm starting this thread to hear everyones take on how to get good gas mileage out of our W124's and as well as what could cause bad gas mileage. To be honest, I'm kind of curious since I've been noticing that my car has been doing poorly on gas lately.

Speak freely.

jrmd01

Chris,

Do a minor tune up (plugs, airfilter, rotor, dist cap) this alone should improve your MPG.

If it's really bad, try changing your O2 sensor. Bad MPG is one of the symptoms.

BTW - I get approx 24MPG on the average.

CDP

Hmm, I'm definitely due for a major tune up. So that should help with my gas mileage.

I'll have to check out the O2 sensor, is that something that can be easily changed?

NorCal124

The O2 sensor is located on the top portion of the exhaust before the catalytic converter. Its pretty easy to change since you don't need the special socket to remove it unlike O2 sensors located on exhaust manifolds. An O2 sensor is pretty pricey. They average between $140 for a universal one that you need to splice into the connector to about $180 for one with an O.E. connector. When I replaced my O2 sensor on my Nissan Sentra my MPG jumped from 26 to 33.

AMG_Fred

holy cow, so only low mileage is the tell for the o2 sensor? or should it just be replaced... i want to change that and the fuel filters on mine...

NorCal124

There are a lot of things that contribute to the loss of MPG. An O2 sensor is one of them. Considering Chris's 300 is a 90' I'm sure it would be a good time to replace it. You're supposed to replace the O2 sensor every 60K. Like jrmd01 mentioned, the plugs, wires, cap, and rotor also help in getting better milage. Even the small things like checking your tire pressure can add up to better mpg.

CDP

I probably won't end up changing the usual plugs, wires, cap & rotor until I have the funds to do a complete full tune up...hell...I'll probably have the O2 sensor changed then too. lol That means I'll have to sacrifice gas for awhile because quite frankly I'd rather get my wheels on.

NorCal124

What I do since I can't afford a "complete" tune up is I buy the parts one at a time and save all of the parts up until I have the time and the rest of the parts to do one big tune up.

CDP

Do you do the work yourself?

I got quoted from my Mechanic around 400-600ish but that's really depending on what I wanted to do. Of course that's including labor, parts and changing everything. Honestly, I can't wait to do the tune up but...wheels first.

NorCal124

Of course. That's the best part of working on cars. There are things that I don't have the experience or tools to do. That's the only time I'll take it to a mechanic. But if I can do the work myself, I'll get my hands dirty. It's also helpful to work on your own ride because you'll discover what else needs work or attention. I also don't like mechanics bull****ting me about what needs work or replacing.

jrmd01

Hey Chris;

Do all your tune up yourself. It's not that hard and you'll save a lot of money, especially since you can buy new parts online cheap. If you let the mechanic do your tune up, you'll be paying full retail price PLUS a small markup for the mechanic to take his profit.

For the O2 sensor, BOSH uses the exact sensor on the 1990 Ford Mustang V8 302. Only difference is the connector and price ($37 vs $140). This is the direct replacement for the W124 300E only. Just cut off the 3 wires and reconnect them onto the Ford O2 sensor.

I'm fighting a surging idle and hesitation on acceleration right now on my car. I'm in the process of changing the MAS potentiometer. If that doesn't work, I'm changing the O2 sensor as I described above.

Beware though NorCal124 is right. The O2 sensor is only 1 small component of the engine that can affect MPG. Along with my previous suggestions, you can also use higher octane gas and it wouldn't hurt to throw in a bottle of techron gas/injector treatment in your gas tank.


LNKPRKSOLDIER - bad MPG is only one of the many symptoms of a failing O2 sensor. Others include rough idle, stalling, etc. I only know this because my car is not running "right" and I'm trying to fix it myself. Mercedesshop.com is a very good website for DIY help. Do a search on that website if you have more questions about the O2 sensor. BTW we have the same color car.

X03

well i dont have the rough idle and stalling like you said....but im only avg. 17-18 mpg.... so yeah i definitely need to look into the 02 sensor. may or may not be the problem, but the plugs, wires, and caps have been replaced so yeah hopefully this can help

CDP

jrmd01,

Thanks for all the information. What you said was pretty much true. I could do all the installation myself, perhaps someone when they have time can write a DIY for tune-ups (including changing ALL fluids and what not/parts and more) so then we can have a Moderator sticky it for future references. Sounds like a good idea, since we don't have DIY topics on this forum. Right now I'm having the same problems as you it seems like. Sometimes I'll have surging idle as well as rough acceleration but then agian I heard thats nothing a good tune up cant fix.

NorCal124

The O2 sensor is what tells the ECU to lessen or greaten the amount of fuel in relation to the amount of oxygen intake for cleaner burning and fuel consumption. An old or malfunctioning sensor can give a false reading and can cause you to consume more fuel.

Lnkprksoldier: Your fuel filter is located in front of the rear passenger side wheel assembly. It will be much easier to get to if you remove the tire. You have to remove a plastic panel to gain access to it. It's lined up in between the fuel pump and I think the fuel pressure regulator. You'll need two wrenches, one to hold the filter in place while you unscrew the fuel fittings with the other wrench. You then have to loosen a screw to remove the filter from its bracket. While I had the cover out I cleaned it up and sprayed it completely with a rubberized undercoat. It cleans up the look and adds a slight insulation against heat and the elements. Good luck.

mhorn

This guy has O2 sensors for $52.50. It says that you have to splice it inot the harness, but a lot cheaper than from the dealer.

http://www.mercedessource.com/

neanderthal

it could also be parasitic drag from brakes, low tire pressure, bad tranny, bad diff, bad wheel bearings and a host of other items.

get a tuneup done first and formost. change your air and fuel filters, and spark plugs. you can do those yourself.

make sure your tires are properly inflated, another easy fix.

change your oils, a third simple fix.

if those dont yeild the fuel economy benefits you are after, then you can change the wires, rotor and cap and so on. ultimately you can then change the O2 sensor. at some point you will no longer get any gains. thats just the way it is.

CDP

neanderthal, thanks for the info.

I really should change all my filters and what not. How easy is easy is it to change the fuel filter and spark plugs? I could totally change them myself but I don't even know where the fuel filter is! lol Any help and directions would be awesome! Or should I just go ahead and have my mechanic do a complete tune up on my car. Then again, It would be nice to save money.

Anyways, I'm due for another oil change. Actually...OVER DUE. I'm debating if I should do it myself. Anything I need to know before doing it? Some members told me to use 5w-40 on my car. It has about 125K miles right now and I'm wondering which mobil one oil I should use. Any idea's anyone?

mhorn

Fuel filter is not hard to find, changing it is a different story. If you're o.k. with high pressure gas spraying in your face and getting axle grease in your hair, then it's not that bad of a job. If I ever had to do it again, I would gladly pay $100 for somebody else to do it.

jrmd01

Update on the Ford O2 sensor. You can get them from Checker's auto parts for $44.99 (w/free local pick up) part number 13953 BOSCH (exact same sensor on the W124 except for the connections. In fact the part number is close too 13925). Recommended interval before replacement is 60K. Don't get any other brand than BOSCH.

http://www.partsamerica.com/ProductL...rtnumber=13953



Chris I can't believe you don't do your own maintenance work. You must be rich. hehehe. I'm so cheap, I try to do everything myself. My mechanic knows when he sees me, my car has a REAL problem.

Most of the work you listed is EASY even for the mechanically challenged owners...It's a matter of taking off 1 or 2 bolts to remove and replace. Do a search for the procedures. You'll never pay your mechanic another penny to do the simple tune ups once you've done it yourself.

1. Changing the fuel filter is EASY, but a little messy/dirty. Shouldn't take you more than 30min to do. I'd rather use that $100 elsewhere....ie taking out a girl for dinner.

2. Air filter is easy, just open the air filter box. Rest is self explanatory.

3. spark plugs - buy a ratchet and spark plug socket. Easy 10min job. Most spark plugs are already gapped to specs...so just Remove & Replace.

4. Oil & filter change takes 30min. It's another EASY job. One bolt to drain.

NorCal124

jrmd01: would that mean if i bought the ford O2 sensor I would have to splice in the OEM connection to it? I work for Kragen (Checker's sister company) so I'm thinking of using my employee discount to save some major cash on just getting the ford sensor instead of the original mercedes one. Another question for you. Have you ever changed the cap and rotor on your vehicle? If you have, did you need to reset the timing on it and how did you do that? I've been told that all you need to do is just replace it but I want to be sure of what needs to happen.

myfirstbenz

Yikes that is bad, my parents just took their 95 e320 on a trip and got 27.8 mpg on the highway. I get 24mpg hwy in my 400E.

AMG_Fred

how the heck do you find out your mileage.....and especially to the the exact decimal
and yes jrmd, hey, are your bumpers painted? mine are... i think my dad chose to get them painted.... too light of a color for my liking

CDP

Math my friend.

NorCal124

I won't give you a hard time about it. Whenever you refuel set your secondary odometer to zero. The next time you refuel divide the number of miles you have traveled by the number of gallons you've purchased and Vioala! Your MPG!

jrmd01

NorCal124,

Yes the Ford sensor I listed (13953) is the EXACT same sensor on the W124. You'll need to splice the OEM connection to it (although soldering it together would be better). What BOSCH did should be considered a criminal crime. I know the connectors are different, but that shouldn't cost us an additional $100. That's great if you can get a discount. I just got the MAS potentiometer today (took 13 days for shipping to Hawaii). I'll install it later this week. If my idle is still surging, I'm changing the O2 sensor this weekend.

Yes I've changed the cap and rotor. It's a direct remove and replace job. I don't remember exactly, but I think there was only 4 bolts that needed to be loosened. You won't have to reset anything. The only problem I had was getting my tools and hands in position to remove the bolts. It's a little crowded around that area. Take off the wires first to give yourself some space to work. It shouldn't take you more than 30min to do that job.

LnkPrkSoldier,

No my bumpers are not painted. If I decide to repaint the car, the bumpers and all moldings will be color matched. Right now I'm having second thoughts on putting money into the car. I'm thinking of getting the 96 E320 W210, or maybe I'll work on my dream car...newer (95?) W124 black sportline coupe 5-speed stick-shift (I don't think it exist. I'll probably have to convert it myself. Maybe Ashman can insert his opinions here).