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#1
12-21-2011, 04:36 PM
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W123 loss of power... fuel?
I'm starting this thread just before I go out and replace my fuel filters.
My '79 300D with 177K miles just began to have power loss. The funny thing is that it only shows symptoms when the car hits any incline, even soft ones. The trans is fine. Smooth and goes thru all gears.(serviced last year) Car starts right up and engine sounds smooth. No excess smoke. On a flat roadway it seems to perform OK but when it gets to about 55 MPH it feels like the dampening effect kicks in. Otherwise the acceleration on a flat roadway seems about normal. i.e. can't really suspect loss of a cylinder. On inclines, the power loss is dramatic. More throttle does nothing. It feels like it is physically being held back. Any incline triggers the dampening effect and the car gradually slows to a 25 MPH crawl. I added fuel additive and fresh Chevron diesel after a highway run. Now I am going to replace the filters. Never had algae due to the City environment and always keeping tank full. Anyway, if anybody has some clues let me know. I'll post later whether the filter replacements helped... (I am aware of the bad fuel 'sticky' but don't really suspect this..)
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1979 300D 220 K miles 1995 C280 109 K miles 1992 Cadillac Eldorado Touring Coupe 57K miles SOLD ******************** 1979 240D 140Kmiles (bought for parents)  *SOLD.SAN FRANCISCO/(*San Diego) 1989 300SE 148 K miles *SOLD 
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#2
12-21-2011, 05:07 PM
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That does indeed sound like fuel filters. If changing the spin on and in line filters doesn't solve the problem, the next step would be to check the tank strainer.
Soon after I put my 300D into service as a commuter (~3,500 miles a month for two years-thankfully no longer) I has similar symptoms, and changing fuel filters helped at first, but then it kept happening even after fresh filters. Pulled the tank strainer (not a terribly fun job unless you like diesel everywhere) and I have no idea how any fuel was getting through the thing. Wish I had taken a picture... Good luck.
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Christopher '06 Mercedes E350 station wagon (silver/black) '85 Mercedes 300D (black pearl/palomino) '85 Mercedes 300SD (smoke silver/burgundy) '79 Cadillac Sedan DeVille '05 Toyota Camry (because always running is nice) '85 Mercedes 300D sold back to orig. owner 8-1-06 '84 Volvo 264GL Diesel, owned 2000-2013
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#3
12-21-2011, 05:29 PM
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That is classic dirty fuel filters. Make sure to change both of them. Report back if the filters don't help. Might also change the air filter. Your tank vent could also be getting clogged. You can test this by pulling the fuel cap off after a long drive. If you get a big sucking sound your vent is clogged. Under the rear of the car there is a little rubber bell on the end of a hard steel line. Make sure that is clean.
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Andrew '04 Jetta TDI Wagon  '82 300TD ~ Winnie ~ Sold '77 300D ~ Sold
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#4
12-21-2011, 08:28 PM
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Newton's law
So it turns out it was gravity's way of telling me the fuel filters were dirty.
At incline, the dirt began to restrict the fuel flow. Replaced both filters and it runs great. Filled the main filter with cetane boost before screwing it in. The in line filter was dark with debri. I had been using a black colored inline filter and I thought it was one of those. That is why eyeballing early on misled me. The clear filter was black with debri. I'll keep an eye on it in order to monitor the strainer. Thanks !
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1979 300D 220 K miles 1995 C280 109 K miles 1992 Cadillac Eldorado Touring Coupe 57K miles SOLD ******************** 1979 240D 140Kmiles (bought for parents) *SOLD.SAN FRANCISCO/(*San Diego) 1989 300SE 148 K miles *SOLD
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#5
12-21-2011, 10:12 PM
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Quote:
You've been doing this for 12 years and you get an issue with fuel filters...............hell I would have expected a person with one post. 
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#6
12-22-2011, 03:15 AM
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Better invest in some Biocide too to make sure you have no bacteria in the tank. Black dots in the primary filter is an indication of it.
I agree this was classic dirty fuel filter symptoms.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.  [SIGPIC]..I also have a 427 Cobra replica with an aluminum chassis.
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#7
12-22-2011, 08:36 PM
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Thanks t walgamuth, I was thinking about that. I'll pour in some Seafoam or Biobor soon.
Well, it has never happened as such before and I'm usually careful to schedule maintenance. So there is a first time for everything. The car is always garaged indoors but all it takes is some water from the fueling stations and biology.... 
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1979 300D 220 K miles 1995 C280 109 K miles 1992 Cadillac Eldorado Touring Coupe 57K miles SOLD ******************** 1979 240D 140Kmiles (bought for parents) *SOLD.SAN FRANCISCO/(*San Diego) 1989 300SE 148 K miles *SOLD Last edited by unkl300d; 12-22-2011 at 08:51 PM.
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#8
12-23-2011, 12:11 AM
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Exact same symptoms as I had recently. The primary filter was black inside. Got some advice here on the forum and put some Startron in my tank. Changed the primary filter as well. Runs a lot better now. I need to look back at the filter to see how it is doing. I am guessing that the initial double dose of Startron broke things up a bit but I need to monitor it.
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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale** 84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds 00 Toyota Sienna 208K (Sold) 15 Subaru Outback 43K 11 Subaru Outback 67K 98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now. 30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60 
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