Poor fuel economy - PeachParts Mercedes-Benz Forum

cavaliers16 · #1 11-04-2006, 09:09 PM

I've searched around a bit about this problem, but each case is slightly different. As I've heard, the 300D gets around 25 mpg city and 30+ mpg highway. Mine gets 15-17 mpg city, 21 highway.

So, things I've checked:
-Filters, screens
-ALDA
What's next? Should I check the timing chain stretch (it has never been replaced)? Should I have the injectors pop tested? I can live with low mileage but it has been getting progressively worse. The PO two owners ago (owned the car for 8 years) kept a log of mileage that I found in the glovebox. He was averaging 29 mpg at the beginning of his ownership. At the end it was averaging just 25. I'm inclined to think timing chain but that will be expensive to fix- one of the many problems with the low income high school job

.

BTW- it burns no oil

BenzDieselTuner · #2 11-04-2006, 09:11 PM

try running some Diesel Purge through the system, and then start always adding Powerservice Cetan booster to every fillup...this should help some....

FamilyGuy · #3 11-04-2006, 09:13 PM

Check your diesel return lines and see if they are moist / wet after a drive. It is a $12 fix if they are leaking

cavaliers16 · #4 11-04-2006, 09:14 PM

I have actually already done that, thanks for the reply though.
I am using the Powerservice stuff every tank. I ran just about half a container of diesel purge through the sucker about a month ago with no noticeable effects.

cavaliers16 · #5 11-04-2006, 09:16 PM

Quote:

Originally Posted by FamilyGuy

Check your diesel return lines and see if they are moist / wet after a drive. It is a $12 fix if they are leaking

Again, thanks for the reply, but no such luck. I replaced all the rubber lines in the car when I outfitted it with the veg system. The steel lines on the bottom of the car are corroded, but (AFAIK) they do not leak.

#6 11-04-2006, 09:16 PM

Fuel leak. If you are not blowing out alot of black smoke, that's most likely the problem.

cavaliers16 · #7 11-04-2006, 09:19 PM

Quote:

Originally Posted by ForcedInduction

Fuel leak. If you are not blowing out alot of black smoke, that's most likely the problem.

It blows a little smoke, but it is more gray in color. It usually smoke on startup for about 5 minutes then the smoke goes away. Could my odometer just be messed up? Just this afternoon I looked at the fuel gauge and trip meter- fuel gauge nearly empty and the trip meter was at 301.1 miles

.

cavaliers16 · #8 11-04-2006, 09:21 PM

I was just thinking about EGR- my car doesn't have it, right? I'm thinking that's 85 and on (?)...

BenzDieselTuner · #9 11-04-2006, 09:21 PM

i go about 400 miles every tankful.......but then im using fancy amsoil fluids and have an intake/exhaust and stuff, plus i run on used veggie oil......

BenzDieselTuner · #10 11-04-2006, 09:23 PM

unplug ur EGR, that should help too..........

the egr is mounted on the intake manifold, and has one vacuum line going to it......

cavaliers16 · #11 11-04-2006, 09:25 PM

I've been having to use diesel all the time now- short trips every day prevent the car from warming up fully (it was cold here today- low 25, high 40). Over the summer, targeting one fillup period in particular, I burnt 15 gallons of veg and 15 gallons of diesel. Got combined mileage of 38. During the summer that was OK, since the fuel was free. Now it's starting to add up.

vstech · #12 11-04-2006, 10:04 PM

odometer could be messed up for sure, check it against some highway mile markers. the MB gauges are known for this failure... majority of them need to be rebuilt.
John

#13 11-04-2006, 10:14 PM

If there are no leaks and no excessive smoke, odometer could be it. Like vstech said, check with mile markers or a following car. The gear can strip, causing it to work intermittently.

I can often get 330miles on my smaller 240D fuel tank.

#14 11-04-2006, 10:32 PM

cavaliers16,

1. I would have the injectors rebuilt, if they haven't been in the last 100k miles.
2. Check out www.turbobrocks.com, it has an awesome volvo forum, but right now it is down from a harddrive failure - it should be back any time now.

sailor15015 · #15 11-05-2006, 12:06 AM

I'd check chain stretch for sure and your injectors. You can build a pop tester yourself out of a grease gun and some easily obtained fittings to see the opening pressure and spray pattern. Its really easy to make. PM me if you're interested. If your chain is stretched the pump will be injecting the fuel late and not combusting the fuel as completely as it would be if it were set where it should be. Plus the cam timing would be late. I think this was the problem on my wrecked '85. Its motor is in my garage now being rebuilt and the chain had about seven degrees of stretch on it. It always got about 18-20 miles to the gallon and I tried everything under the sun to fix it. My '84 gets between 23-24, sometimes up to 26 on interstate trips and it only has about two degrees of stretch.