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  #1  
Old 09-04-2002, 12:02 AM
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300SD bad mpg

I just overhauled my cyd. head on my '84 300SD doing everthing.
Overhauled the injectors and got a rebuilt tubo. My car starts and run's great, has a lot more power ...but I am getting only 20-22 MPG. A few months before the work I was getting 25-27 MPG...and then it started getting worse until it was smoking bad and getting 19-20 MPG on a good day, with little power. I did a leak-down test and knew my tubo was sick, so I did the repairs and it runs so good now I almost hate to do anything else, but I should be getting better mileage. I am thinking the timing might need to be checked/changed or my tubo is not working correctly. Anybody get any ideas why I'm not getting better mileage?

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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car

Last edited by CHAPP; 09-04-2002 at 12:44 AM.
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  #2  
Old 09-04-2002, 04:34 AM
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No one has an answer??? I searched and got mixed results....but seemed to point me in the direction I was going in. It's hard to beleive that people would rather discuss a ball joint or trying to run-up miles on a MB. What's wrong with my subject?
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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car
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  #3  
Old 09-04-2002, 12:47 PM
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Stumped

Chapp, I believe you've stumped em. Your problem is like some of mine, which is to say more complex than the usual things you see posted here. Sounds like you are probably already on it.
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  #4  
Old 09-04-2002, 02:43 PM
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Definitely check your injection timing, and also the cam timing too see if the chain is stretched. Turbo output can be checked with a simple pressure gauge, should be 12-14psi at full load, ~4000rpm, in 3rd gear. Low turbo output doesn't affect MPG very much if at all, it mostly just kills power! BT, DT.



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  #5  
Old 09-04-2002, 07:38 PM
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You will get better milage if you drive it like it ran before the turbo died. Keep rpm under 2000 as much as you can. Horsepower uses fuel to make it, the harder you drive, the more fuel you use!

Also, you need to check timing and chain stretch. Late injection and valve timing will cause low power at low rpm, using more fuel.

Check tires, shocks, and brakes, too -- also front end alignment. Anything dragging (brakes or tires) or wheel tramp, will eat up horsepower.

Finally, check the aux fan for operation with the AC on -- if the head pressure is too high because the fan doesn't run, the engine will really have to struggle to generate the power you want, it's all eaten up driving the AC compressor against excess head pressure. This is why I spent $175 on a new electric fan for the Volvo (two salvage ones died).

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #6  
Old 09-05-2002, 12:18 AM
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Thanks Guys...I knew I would get some ideas. Well I checked my tires and pressure was fine...same Micheilns that I got 25 MPG with. No difference in milage with a/c on or off, when I turn on the A/C the fan comes on. 5000 miles ago I replaced timing chain and all the rails in there...checked the chain stretch when installing the head. I guess my transmission is due for service ...I will check that to. I put trans. in nuetral (40MPH) and it coasted fine, and stopped in a straight line...so no brake drag. But I'm going to re-time the engine and since the cam was just installed I know it is right...MB specs. I drive the same way I always drive...but don't seem to hear any turbo "whine". I'm going to check the boost one day this week and will keep everyone posted. I didn't think you guys could be stumped....and I was right!
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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car
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  #7  
Old 09-05-2002, 12:29 AM
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FYI, a tip is to set the injection timing to the far side of spec advanced. Meaning if spec is 24 ATDC +/- 1, set it to 23, not 24. You can pick up a smidge of power & MPG this way. I went 2 degrees advanced on my car and it made a noticable difference in MPG and low/mid RPM power, but I did get some smoke at full throttle over ~4000rpm which was not there before. I plan to set it back to only 1 degree advanced but haven't gotten a round tuit yet, as usual (I keep getting square and triangular tuits for some reason.)
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  #8  
Old 09-05-2002, 12:48 AM
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Dragging rear brakes won't pull the car enough to notice, just eat fuel.

Bad wheel bearings will also eat fuel -- front ones pull if they are really bad.

Don't know what else to say, except check the odometer. You will be getting really bad milage if the stinking thing isn't recording the miles correctly. I was down to 18 mpg (indicated) before the odo quit all together on the 220D!

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #9  
Old 09-05-2002, 12:59 AM
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Guess I will check the brakes a little closer...wheel bearings haven't been done for 20K...easy enough to do when checking the brakes. The odometer...I will get my GPS out and check it out...all good ideas
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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car
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  #10  
Old 09-05-2002, 11:08 AM
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Quote:
Originally posted by psfred
Don't know what else to say, except check the odometer. You will be getting really bad milage if the stinking thing isn't recording the miles correctly. I was down to 18 mpg (indicated) before the odo quit all together on the 220D!

Peter
i went from 23 mpg to 17 mpg in course of one week! sure enough, it was the odometer.

turns out that both the odometer and speedometer are off by 17.5%, as i found out during an extended highway trip (used the mileage markers and my watch's tachymetre). when i got home, i plotted my trip out on mapquest and then recalculated my mileage.

turns out i'm getting close to 27.5 mpg!
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  #11  
Old 09-05-2002, 12:44 PM
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just my .02 - have you tried changing the brand of fuel you use?
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  #12  
Old 09-05-2002, 02:33 PM
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Just spot checking the odometer might not catch your problem. When mine failed it would hang on 9 sometimes. It might run 50 or 75 miles and then hang up for a few miles. The speedometer continues to function, so you have keep an eye on the odometer to spot the hanging up....the most difficult diagnosis is the intermittent failure.
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  #13  
Old 09-05-2002, 10:52 PM
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Diesel Purge then quality gas (I'm currently using Amoco 50 cetane and it is awesome).
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'84 (11/83) 190D 2.2 5-Speed; Silver/Blue; Motor No. 00354, 402k mi (340+kmi mine)

'89 Porsche 911 Turbo Coupe; Black/Black; 53kmi
'05 BMW 530i 6-Speed; 302kmi
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  #14  
Old 09-07-2002, 11:53 AM
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Well I have used standayne performance formula for 6 months and change my fuel filters often. I hooked up my GPS for a few day...and my odometer and the GPS agree on the distance I went and how fast I was going, I drive the same route every day. Checked all the brakes and went straight to the 13mm wrench to advance the timing. I am all the way at the end of advance and have to take the pump out and twist the shaft and re-install. I am going to buy the the little piece of fuel line and time it according to my MB book(CD)....maybe 22-23 if its at 24. Any one know a shortcut??
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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car
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  #15  
Old 09-07-2002, 02:27 PM
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There may be a shortcut to set the IP timing on your car. Look at the side of the injection pump, toward the lower rear, and see if there is a 17mm hex head "bolt". If so, you're in luck - this is a plug that you remove and use the hole to insert a tool from MB. Look at the photo at the URL below, which shows the MB tool where the plug normally is (it's the black thing with the red cap in the middle):

http://www.meimann.com/images/mercedes/head_gasket/IP_left.jpg

The tool costs ~$20-$25 from your dealer, or a bit less from aftermarket sources - just make sure you get the OE Mercedes tool, NOT any other brand! It must have the Mercedes logo & part number on it (601-589-05-21-00).

The tool is designed to be used when installing the IP after removal - you carefully turn the IP shaft until the "lug" is visible through the hole, then insert the tool to "lock" the IP in place. Then, with the engine set at the proper setting (24 degrees or whatever) you insert the IP into the engine, remove tool, and you're done. Well, not quite, you should turn the engine over 2 revolutions and make sure it's still timed properly. (Especially on the OM60x engines... I had to R&R the pump about 4 times before it worked properly - that damn timing advance mechanism caused it to act up!)

However, you can also use it to check/set timing with the pump in the car. You turn the engine to within a few degrees of spec, assuming the IP's current setting will be near there. Insert the tool (which is spring-loaded) and slowly turn the engine a smidge at a time while "feeling" for the tool to engage. When it engages, read the number off the crank indicator, that's your current timing. After checking mine, I turned the crank 2 revs but this time set the crank where I *wanted* the timing to be. Then I loosened the IP and rotated it until the tool popped in place & tigntened it all up again.

Warning: DO NOT turn the engine, or rotate the IP, with the tool locked in place!!! You may damage or destroy the IP! Remember to always loosen the tool and "pull" the shaft out!


The procedure is really much more simple than it sounds, and is MUCH easier than fussing with the messy, annoying drip method. The tool works for all OM60x engines (the later aluminum-head models) as well as the late OM617.95x turbo engines (1984-85, I believe.) If you have a fleet of MB diesels, and like investing in cool tools, Mercedes also makes an electric version that plugs into the same hole. This one you can leave connected while turning the IP or engine and watch for the lights to come on that indicate the timing. It's $225-$350 depending on who you buy it from. Here's a photo it:

http://www.samstagsales.com/images/mbabbox4.jpg



Good luck,

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