My 1997 e300d mileage is decreasing and I can't figure out why. The car still runs great and I have replaced all the fuel filters, air filters, and am running synthetic oil in the engine. The car has about 110,000 miles with no sputters or misfires.
I bought the car in March last year with 78k on the car, which had a recent complete service. I since, have replaced all the filters, but when I first bought the car, I was getting 28/34 (city/hwy) mpg, now I am lucky to get 22/28 mpg. I average around (20/26) which is not acceptable. I had an Acura that was getting the same mileage and I sacrificed performance for ride and mileage by buying a diesel, now, I constantly re think my decision. Can anyone shed some light?

 

It may be a number of factors that come with milage:

1. Injectors clogging/wearing out.
2. Timing chain stretch
3. Injection pump timing.

It could also be the fuel you are using has changed, but otherwise I would check above. Also, have you checked the OBD system for any codes?

 

You reference an ~25% decrease.

i'd look for a fuel leak or wetness somewhere on or around the IP, although with a leak big enough to lose 25% of your fuel it probably wouldn't start. But, look anyway.

BTW - What size tires are you running?

 

Are you using the heater booster (if fitted)? This can use alot of fuel.

Is the engine reaching operating temp (80-85C)?

Are you down on power? You may have a blocked cat/exhaust.

Justa few things worth checking.

 

I ran some BG injector cleaner through the fuel system, which really made a difference. I am running my first tank so I won't know until I refill, but there is a definite difference in the performance.

 

I did the exact same thing tonight! I'm hoping the engine surging goes away - seems to have significantly lessened.

 

I have run through two tanks of gas and the mileage is still decreasing so the problem was never solved. To answer some of the other responses, There are no leaks or evidence of any leaking. The injectors could be the problem, but the mechanic has taken them out for a surging problem and checked them and they tested good. I guess the timing chain could be stretched but there are only 110K miles on the car. I assumed the 100k mark was the break in time for diesels, but the gas mileage is still an issue. I average 500 miles per tankful in both highway and city driving and 600 miles on the road. Prior to this I was averaging 600 miles all around driving and close to 750 miles in highway driving alone.
I thought the injector cleaner would help and it does run smoother, but the mileage has not changed.

 

Injectors OK ahd those checked. Timing chain? car has 110k miles, could it stretch that soon? Injection pump timing may be a culprit.

 

Standard size.

 

Temp is between 80-100C but according to several mechanics, good. POwer is good.

 

Both things depend on the use of the car. Checking the chain stretch is not difficult though.

 

Correct tire size is 215/55/16; any other size WILL effect the odometer and therefore your results dramatically.

Surging problems in that engine usually have to do with sticky resonnance or egr flaps. Removing the crossover/IM and cleaning everything often helps as does ensuring there are no vacuum leaks at the transducers controling them..

606's arent known for chain stretch. They are not under as much tension as prior engines.

 

The surging is an oddity. I have taken the car to the deal for extensive testing, but instead, the dealer had an inexperienced mechanic working on the car and he ended up shorting out several compenents in the engine...then of course, wanted to charge me for unrelated repairs.
I have replaced all the flaps and checked for vacuum leaks, replaced all selas etc. THe surging has been expensive! MBUSA claims there are no issues.
I talked with a few race mechanics (we have Barber Motorsports Track here, a wold class facility) who thought it was the fuel pump timing, so I am taking the car to a speed shop to see.

The size of the tires is 215/55/16, and I have acid bath cleaned the crossover tube as well. I don't know how to check the timing chain, but that is another issue I'll check after the fuel pump timing.

 

How do I check if the timing belt has stretched? How do I know if it is stretched and where do I look?

 

Neither chain stretch or pump timing are issues on 606's and the fuel/lift pump and Ip are both mechanical. They either work, or they dont. No fuel surges, no on again off again.

Air flow IS a major issue on the 606.910 & .912's.

Go to a different dealer if yours doesn't have someone conversant with the 606.

 

I have had all of the valves changed in the car, no codes are coming up. I did read in a previous post that the surging may be a result of a faulty wiring harness, with which Mercedes has documented issues.
The post related to the car cutting power and surging, and made reference to white puffs of smoke coming from the exhaust when the car sputters, exactly what mine is doing, yet none of the mechanics who have looked at the car have been able to isolate, nor find any issue with wiring. I would not think a timing chain would stretch after 100k miles, nor would I think the fuel pump timing would retard form its original settings, but I guess it is possible. When I bought the car, it didn't sound like a diesel at all, but around 85k, when the issue began, the car started sounding more like a diesel (with the familiar click,clack of the engine). I did find that the fuel made a difference in the frequency of sputtering. One of the large local suppliers is very consistently supplying bad fuel so when I fill, I have to go to a particular station, or find out who the supplier is and go elsewhere if it is the one in particular that has bad fuel.
In addition to changing out all the valves, I have changed the fuel filters, checked for mold in the tank, checked the screens for sludge build up, and acid washed the crossover tube.
To be honest, I have spent way too much time and money on the problem, but I wouldn't feel right selling the car unless it was repaired properly, and it is irratating to drive with the way it runs. My last tank I averaged a little less than 21mpg and the highway driving, I barely got 24mpg, so I know there is a problem, I just can't isolate it for repair, so any input is greatly appreciated.
I have taken the car to the Mercedes dealer, and two other local mechanics. The most inept mechanics seem to be at the dealership, Crown Mercedes, the other ones left Crown and have their own shops and are certified Mercedes diesel mechanics.

 

Not clear on what valves you refer too.

I'm suggesting you look at the resonance flaps and EGR valve flaps in the intake manifold and crossover pipes. THey control airflow to the engine and make adjustments based on fuel supply and engine load. They get sticky with sludge and the electricly controlled vacuum trancducers can also become dodgy.

When not operating properly the result is a 50-100 rpm surge at freeway speeds. Pretty classic complaint on the .910 & .912 engine.

Biodegradable harness's were last seen in 95. '96 on used a different insulation.

 

The valves I refer to are the resonance valve, the egr valve, there are two other valves, an upper and lower, all have been changed. THe crossover tube was acid washed as well. The codes I was getting were for the resonance valve which was replaced after acid washing the crossover tube, so if there is an aspiration problem, none of the mechanics I have taken the car to have been able to find. The car does not have any faulty codes, but still sputters from time to time. I knew there were issues about the biodegrading harnesses, prior to my year, but there were still issues relating to the wiring harness failing. All symptons should have or indicate a faulty code, but they are not showing up.
I have thought about selling the car, but it's hard to sell a car when there is a problem and I am not the kind of person to do something I consider unethical anyway.
I went to Atlanta this weekend and averaged 26 mpg on the road. The city driving is still hovering around 21mpg, WAY too low for that car.

 

See posts 37 and 48 for tests you can run to confirm both sets of flaps are operating correctly.
http://www.mercedesshop.com/shopforu...d.php?t=222197

 

I am with Allison:
On all forms, everyone with older (Pre 606.9x) motors talk about timing belt stretch, IP timing. It would be great if the forms would split out the different motors.
My 97 E300D, has the same surging problem as all 96-98's have. I expect that in the 96-97 Non turbos can feel it better. Put it on curse control about 55mph, and 80% of owners will have felt it at some point during their ownership. In the Snap on manual for MB engine Comm. page 126 details how to check them. If you have the car at a MB dealer, have at tech go for a ride with you, while the car is hook up to their scanner..
I haven't fixed my car yet, because I don't want to spend money while some fool shot guns parts at my expense. This manual is the first place I have seen where their is diagnostic approach.
Regards,
Bill

 

Ever consider your calipers are frozen/brakes dragging? How about the trans?

 

Brilliant suggestion to check brakes and other running gear...
Have you put on wider tires? Checked tire pressure? Remembered to lift out the sandbags from the trunk after the last snowfall? Just guessing...

 

So the dilemna continues. MrBilly, I talked with a few old time mechanics, both said the timing belts should not stretch and the engine can be rotated to adjust the timing. I spent $800 on a new belt.
I am not sure if the car I have is a lemon, but let's just say the mechanic and I are on a first name basis and he recognizes my voice when I call.
I have contacted MBUSA and they do not care. I sent MBUSA a certified letter regarding the surging and received no response. I have talked with the regional area manager and he seemed unsympathetic as well.
The car surges, usually on start up and if it happens and someone gets hurt, MB gets sued. As far as the mileage decreasing, I am hovering around 23mpg in town adn 28 hwy, still way too low for this car. I think the problem all along, after spending over $6,000, is not really the issue, I think the car is a lemon.
MB brags on quality, but there are too many mechanical problems, and the interior is falling apart (I do keep my cars clean and detailed 3 times a year), the seat is splitting and the headliner is beginning to fall. Although the car rides nice, it has cost too much money and there are too many safety issues to continue.
I think this is my last MB.

 

You may know this mechanic well, but what are his qualifications with MB and specifically diesel MB?

Any chance it is your mechanic's inability to solve the problem (or that he has not performed the work properly)?

 

sell me your 1997 diesel, I dont care what issues you have. I work on mercedes, I live in pelham. I can convert it to run on waste fryer oil, i run my 97 e300 on it with out a problem. Maybe you've seen or smelled me around town.
i dont work at crown i work at jack ingram mercedes