300sd Mpg - PeachParts Mercedes-Benz Forum

bbergman · #1 12-22-2003, 09:46 PM

My 1983 300SD is running much better and smoother after, 1. Changing all filters. 2. Disabling the EGR. 3. Adjusting the valves. 4. Adjust the ALDA 360 ccw. 5. 2 cans of diesel purge. It has 183k (293km) on it, I run Mobil 1 15w50. I had some pretty good nailing at idle, which is greatly reduced after the diesel purge, but some nailing is still there and there is a slight miss at idle. The nailing and miss disappears just above idle and it runs good from there on up. I am only getting 26mpg to the imperial gallon which would be 20.8 US gallon (combination city and highway driving). I am in Toronto Can., the weather is getting a bit cold to work outside. Smoke does not seem excessive but if you stand on it there is some balack smoke. Turbo spins fine and no play. Where to look next? I have read guys getting 26-29mpg US gallon which would be 32-36 Imperial. Any help would be appreciated.

Brad

BoostnBenz · #2 12-22-2003, 10:03 PM

It almost sounds to me as a bad injector or two. Oh since you got all of that stuff done perhaps it'd be good to clean the banjo bolts going to the ALDA line as well.

bbergman · #3 12-22-2003, 10:28 PM

I forgot to mention that I did the Banjo bolt already. Do you think a disassemble and clean or have them rebuilt? I drive it daily so I don't want it down for more than a weekend.

Brad

BoostnBenz · #4 12-22-2003, 10:56 PM

Well it is the same work to clean it as it is to rebuild it, just it costs a bit more (a few hours in total for removal, cleaning, and installation). Theoretically whether cleaning or rebuilding they should be popped tested afterwards. You can buy the nozzle for about $25ea, that is the only part that really wears on the injector. After my own cleaning experience I'm not impressed with rebuilt injectors and don't recommend going that route. If the diesel purge made a bit of difference then odds are it is the injectors however I wonder how much cleaner they can be after running two cans of it through!? If you have the tools to get the injectors out all you need extra is a vice and a clean work area to sprawl your parts upon.

psfred · #5 12-23-2003, 11:27 AM

Check the timing chain for stretch -- I'm guess it is at least 8 degrees.

Typical symptoms -- excessive smoke, especially at high load and speed, lumpy idle, and injector knock, bad fuel milage.

Most are symptoms of late injection timing, but if the chain is worn, replacing it will fix both the late injection timing and the late cam timing at the same time.

Peter

vwbuge · #6 12-23-2003, 11:26 PM

I've done pretty much the same thing to my '85 and I get 18 mpg.
She has 301,000 miles

BoostnBenz · #7 12-23-2003, 11:32 PM

Well VWbuge yours is sort of an exception to normal, unfortunately nobody can find out what is causing the poor mileage. Isn't it more like 21mpg after the corrected mileage?

tjohn · #8 12-24-2003, 08:23 AM

BBergman - Like Psfred mentioned, your timing is probably retarded. After trying the things on your list, plus a few others, (tire pressures, dragging brakes, checking for fuel return line leaks, and so on) I adjusted the timing. This was enough to give me a bit more power (0-100km went from 18 to 16 seconds) and sneak my mileage up to 24-25 U.S. from the 20-21 I was getting before all the adjustments. I'd still like to get it a bit higher, but I feel like I can live with 25. Also, up in Canada I imagine that you've got a pretty serious winter blend on your diesel, that definitely can drop the mpgs a mile or two.

bbergman · #9 12-24-2003, 04:37 PM

The chain has been done. I will go at the injectors and timing. The parts stores closed up early today for Christmas so I could not get the injector parts, job for next weekend. I'm ordering a Mityvac too so I can track down some other vac related problems. I appreciate the help, this forum is great. Just gotta do some searching. I'll let you know how I make out. Ya do get to love diesels.
Merry Christmas!

Brad

vwbuge · #10 12-24-2003, 11:45 PM

What do you mean 21 mpg after the corrected mileage?

BoostnBenz · #11 12-25-2003, 12:19 AM

Don't you have oversized tires which accounted for a couple mpg difference after correcting?

vwbuge · #12 12-25-2003, 04:29 PM

The difference is so small that is insignificant to total numbers. I think I figured it one time to be like a 2% difference.

vwbuge · #13 12-25-2003, 04:35 PM

Sorry, more like 5%.
Somebody jump in here and correct me if I'm wrong.
It says that when my speedo reads 60mph, I'm actually going 63.
Wouldn't that mean if I go 60 miles(according to speedo), I am traveling 63 miles?
Shouldn't I show better than actual mileage?

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

whunter · #14 12-25-2003, 05:20 PM

Hello Brad
Cleaned or rebuilt injectors are never as good as new.
If you can afford them; get new ones.
RE: I had some pretty good nailing at idle, which is greatly reduced after the diesel purge, but some nailing is still there and there is a slight miss at idle.

You have at least one bad injector.