Why have I dropped from a near consistent 28-31 MPG from my 87 300 D???

The engine has now 220K, filters are changed every 6y months, Tom in Colorado rebuilt my injectors (are fine) engine has good compression, egr is plugged off, boost sytem working properly I think, IE...little change from alda, or a 12 second mile, yet my mpg seems to be between 25 and 28 around town and now can't see 31 mpg, the economy I got up until recently.

?? What can drop fuel economy???

My timing is set at or approx 15 degrees ATD.......proper for the 603.....but at 220K on the engine, is it possible fuel economy is passed because of the possible need for a new timing chain?

25mpg in town seems reasonable, I don't see how you could achieve 31mpg city unless you never used boost.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Don't see the problem, 25mpg city is about right. I wish my SDL would get that.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Don't forget to check your air filter. Make sure your calipers aren't dragging either.

You can't verify a consistent drop in fuel economy without an array of statistics on hand over a given time period.

Mileage varies for me about 26 - 30 mpg around this time of the year for my SD and SDL. Granted, most of my driving is highway, my results can vary. Even though my driving habits remain unchanged. Right now I'm getting about 26.5 - 27.5 mpg.

Sometimes, when I get a really poor tank of fuel, I notice increased particulate emissions, and a significant lack of power (similar to when the turbo is not providing full boost). I compensate by adding Diesel Kleen to the tank, at their strongest recommended ratio. This raises the cetane value of the fuel, helping the fuel to ignite more evenly, plus it seems to improve the power per gallon density. Mileage improves by maybe 5%.

The 300D, driven in the city, should net about 28 mpg....MAYBE 30. The EPA originally gave the 300D figures of 25 city and 31 highway. This was with the trap oxidizer in place. The '87 SDL was rated at 22 cty - 23 hwy. The previous year, the federal version of the 300SDL scored a 25 city - 27 hwy. A difference of 12% for city and almost 15% highway. So, the EPA would grade the 300D w/out trap ox at 28 mpg city and 35 mpg highway. FWIW, I find the EPA figures for Mercedes pre '93 - '94 far more accurate than later calculations in real world driving.

The oxidation catalyst, if it is flowing freely and serving its purpose, should not hamper fuel economy.

__________________
1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)