low mpg, weird gauge
 

Hello again.

I'm currently having some fuel issues. When I fill up the tank, I stop as soon as the pump stops. I don't top it off. When I start it up, the gauge doesn't quite make it to the "F" mark. So maybe the needle is a little off, right? Well, the other day I was driving to work - 13 miles - and I was getting close to being on E. The station with the cheapest prices is close to work, and judging by the amount of fuel it looked like I had left - not quite on E, and the fact that with a full tank the needle doesn't quite hit F, I figured I'd should make it no problem. Nope. First time I've ever run out of gas. Or fuel in this case.
I filled up the tank and reset the trip meter. When the needle was at 1/4 tank, I had only driven 275 miles. Not cool. I'm averaging under 17 mpg. I compared it with highway mile markers and the trip meter and odometer are near perfect. Most of my driving is city, averaging about 40 mph and a little highway, mostly in traffic, but sometimes up to 75 mph.

Now then. There is a bit of black smoke. It seems like it smokes more than it should. I see a guy driving a 300SD on my way to work sometimes, and mine definitely smokes more than his. So what's this all about? I did a two can diesel purge less than 1000 miles ago.
Also, when I had the hood up the other day, I noticed that the banjo/alda line had come unplugged at the banjo. It was short and brittle, so I replaced it. I don't know how long it was unplugged. Could that lead to a decrease in fuel economy?
Also, I have significant flare between 1 and 2 and a little from 2 to 3. I try to manually shift it, but it's hard when you're trying to get going from 1 to 2. Could the flaring be burning a lot of fuel?
And finally, there's a crack in the downpipe. I'm not sure if that could effect fuel economy or power.
What should I do? Change fuel filters? The pre-filter is a little dark but not bad. The air filter is also a little dirty, but not that bad.
I'm trying to save for a WVO kit, but in the meantime I'm blowing all my $$ on overpriced diesel for a car with really poor fuel economy. :(

anyone?
 

Today the needle is at 3/4 full and I've only driven 60 miles since I filled up. :eek:

Anyone? Help?

You should replace the fuel level sending unit. They go bad all the time, on my SD its the same way the fuel needle will jump around from half to 1/4 although most likely you have half in the tank.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1SK03OVBJ1XU0OGAC5&year=1984&make=MB&model=300-SD-002&category=All&part=Fuel+Level+Sending+Unit

okay. but...
 

If the fuel level sending unit is broken, is it possible that I would run out of fuel even if I still have fuel in the tank?

Like I said, I fill up and the needle doesn't get to 1/1. I ran out of fuel on the highway, and the needle wasn't quite at R.

I guess I'm just asking what the function of the fuel sending unit is, besides obviously sending fuel. Is it broken and that's why I'm only getting about 15 mpg - now even less. Or is it broken and I'm still actually getting about 28mpg, but it's causing the gauge to be off and making the car think it's out of fuel?

Zounds, that's expensive. Can this part be serviced instead? Mine is pretty flaky too, but the idiot light works thank god.

fuel senders only send a message of how much is in the tank. they have nothing to do with the actual fuel system. maybe you should check for leaks. check/adjust valves. how is the cold start?
get a good air filter (mann, hengst, or wix-napa gold) and possibly change fuel filters. when were they last done? since you ran the tank dry, you may have sucked up some nasties.
how are your inj. return lines(the cloth covered ones that loop- from inj. to inj.) the are cheap and easy to replace. seems like that poor of mileage would come from a leak.

my$.02

Some tips
 

Here are some things to try...

If you are smoking a lot, try adjusting the ALDA. It could be that a previous owner adjusted it way rich, especially if the boost line to it was not attached. Try adjusting it clockwise and see if your smoke clears up.

The secnd thing to try is a valve adjustment. the valve adjustment is crucial to this engine. if the valves are out of adjustment, your fuel economy and performance will suffer. I do not think you have any isues withthe fuel guage or sender. in a 300SD you should be getting at least 400 miles between fill ups.

How many mies are on the car, how long have you owned it and how is the performance?

Good luck

other info
 

The car has about 180k miles, I've owned it for 3 months. If I didn't have the flare between 1 and 2, my 0-60 would be pretty good. It starts up 99% of the time on the first turn, 1% of the time it takes a fraction of a second longer.

I had it checked out at a MB dealership. They said it could probably use a valve adjustment, but that it wasn't that bad.

When you say adjust the ALDA clockwise, are you talking about turning the plastic piece on top?

My cloth hoses look good. Sorry about my lack of part knowledge here, but there is a coolant hose that goes into a plastic box thing right in front of the fan at the very front of the car. The male out that that hose goes into looks like it's melting and cooloant is leaking a tiny bit from there. It hisses a little when the engine is hot.

I'm going away for a couple weeks. When i get back I'll change my fuel filters and my air filter. I also plan on changing to 5W30 Mobil1 Turbo Diesel Oil, and I think I chould probably have the ATF drained and refilled.

Any clues as to why the fuel gauge needle doesn't hit 1/1 when full and at the same time I run out of fuel before it hits R?

Judge your fuel mileage only using the odometer and the amount of fuel you add to the tank. Judging by the miles you travel and the fuel gage will not be an accurate indication. Good luck, congratulations on getting your car, enjoy it.

My fuel gauge pretty much works the way yours does, JimZ. If it is filled up only to the point where the pump clicks off, the needle doesn't make it to full. Typically it will be down at 1/4 after I've gone about 250-300 miles, depending on the fuel quality and whether it's B99, B20, etc.

However my actual mileage doesn't suffer. I seem to have quite a bit of fuel left after the light comes on.

I should say that when the attendent (OR - not a self-serve state) continues to fill the tank after the pump clicks off, the gauge can make it to full.

i am having the same problems as well, however, there has been times that i have had the reserve light on, and topped it off, to find that there are still 6 gallons in the tank!!!!

sad to say it but i also ran out of diesel headed to school one morning

and another question, there isnt an actual seperate reserve tank, is there?