Bad fuel mileage????? - PeachParts Mercedes-Benz Forum

vwbuge · #1 06-03-2003, 11:47 PM

I've been getting around 18 MPG gallon around town. ALot of hills around here. Haven't had the poor girl on a long highway trip lately to check HW miles. What does your 300SD get around town?????

DslBnz · #2 06-04-2003, 01:08 AM

Could be just a bad batch of fuel. It happens. Once I got about 17mpg in my 300SDL. I usually average around 26 - 28 in town driving.

JerryBro · #3 06-04-2003, 07:05 AM

Our 84 gets about 28, the 83 gets about 22.

Jerry

BHCULP · #4 06-04-2003, 09:19 AM

I have a 1983 SD, and I filled up the tank and it took 27 mpg. Hope that helps! BHCulp

TX76513 · #5 06-04-2003, 09:34 AM

Lot of interstate driving she will get 27 - 29mpg. Stay in town and have my toe nails in the firewall alot 23 - 26mpg. For this big and heavy of a car I have no problems with either range.

vwbuge · #6 06-04-2003, 09:54 AM

So where should I start for a tuneup? Valve adj??? fuel injectors??? The motor pulls strong and starts and runs fine. Although, it does have 297,000, I would expect a drop in fuel mileage, but the damn thing runs so good.

TX76513 · #7 06-04-2003, 10:48 AM

So where should I start for a tuneup? Valve adj??? fuel injectors???
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Personally I have been a fanatic with fuel injection timing, valves and injectors. More so with the 300D than the recent SDL. Valves are not as bad to do once you have someone show you the ropes. I had trouble digesting the DIY threads for valve adjustment - but once I had the ole "show me" from a knowledgeable person it all made sense. Due diligence on those items always kept my mileage at a norm. With that said I am sure in later post we will here the inevitable "if it's not broken don't fix it" - and I agree with that to an extent as well. What do you know (history) on the injectors?

vwbuge · #8 06-04-2003, 01:46 PM

I have extensive records for the car. MB serviced to 110,000 miles then owner maintained up to when I got it. I see all sorts of things replaced but no mention of any injector work. Time to rebuild or replace? how hard is it to adj valves? I have a '67 VW in which I do the valves all the time so I am not totally blind to it.

300SDog · #9 06-04-2003, 02:38 PM

My guess is you've got at least one injector pissing fuel into the chambers. I would pull them all and take em to technician for testing and possibly installing new tips. Does the car seem to be sending unburnt fuel out the exhaust pipe?

Tune-ups dont mean alot when you are working with worn out parts.

Otherwise, an often overlooked problem that causes bad mileage can be fuel leak somewhere along the line from fuel tank, like at rubber hose connections.

TX76513 · #10 06-04-2003, 03:20 PM

You will probably find these to be very helpfull - there is some extreme talent in this forum.

Valves and Injectors you have to check out Thomaspin's site
THOMASPINS EXCELLENT WEB SITE

Go to Cars -Techincal -Motors then pick you pleasure

Injection Timing
Stu's Excellent MB info

You have a wealth of information here on this forum.

Joe Blowe · #11 06-04-2003, 11:30 PM

Quote:

Originally posted by vwbuge
So where should I start for a tuneup? Valve adj??? fuel injectors??? The motor pulls strong and starts and runs fine. Although, it does have 297,000, I would expect a drop in fuel mileage, but the damn thing runs so good.

My vote: Always start at the odometer. Have you done a mileage check on the highway yet?

297,000 miles on an odometer -- might just be out of whack...

vwbuge · #12 06-05-2003, 12:02 AM

Well, I did install new tires/wheels. I went from stock (205/70-14) to new stuff (225/60-16). BUT, using this website I calculated the mileage to be off an insignificant amount. Per 200 miles traveled it is only off by like 1 MPG.

http://www.miata.net/garage/tirecalc.html

leathermang · #13 06-05-2003, 12:15 AM

If you pull the injectors and they test out fine.. then consider pulling the precombustion chambers while you are there... the small holes in them must be clean and unobstructed to get the mileage you should.
They are not much trouble when you already have the injectors out.... and they are critical to good performance...
When you do your valve adjustment be sure to check your chain elongation at that time... also no problem since you are already there.... and critical to the valve and injection timing .

Joe Blowe · #14 06-05-2003, 01:51 AM

Quote:

Originally posted by vwbuge
Well, I did install new tires/wheels. I went from stock (205/70-14) to new stuff (225/60-16). BUT, using this website I calculated the mileage to be off an insignificant amount. Per 200 miles traveled it is only off by like 1 MPG.

no, i'm not referring to your tire/wheel setup. you might need to have your speedometer/odometer calibrated.

when i bought my wagon, the speedo/odo was (and still is) off by about 17 percent. makes my mileage seem really crappy...

vwbuge · #15 06-05-2003, 09:14 AM

So where can I get these things tested???? The only place I can think of is a small garage that services and sells International tractor-trailers...........