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#1
03-13-2007, 06:05 PM
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Fix Your RPM Sender in Less Than a Minute
This is a tutorial on fixing that intermittent RPM fluctuation that most of us suffer from. Ive noticed that my RPM comes alive with increased engine heat, but never cold. This appears to be caused by the expansion of the silicone material within the sender unit. Why not apply some pressure to that silicone to simulate heat expansion? Try this:
Fig 1. Locate your RPM sender unit. Mine is located on the drivers side fender wall.  Fig 2. Unscrew the upper half of the sender unit with your hand. No tools required.  Fig 3. Pop the sender cap away from the sender plug. This requires a bit of force, and should be accomplished easily by pulling. Pictured here, you can see the top side of the plug in white. This seems to be a silicone like substance that insulates the electrical connections inside the unit.  Fig 4. Fit a crushed piece of tinfoil and press it to shape on the silicone area. I used a piece about 2mm thick. Pop the screw cap back on the plug.  Fig 5. Reinstall the unit. You will feel the extra pressure created by the tinfoil being compressed within the unit. This is the desired effect. Start the car, and see if it works. 
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#2
03-13-2007, 06:18 PM
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That's an old-school trick that's been passed around for a LOOOONG time... The most common variation used a "cigarette butt" instead of foil.... but the result is the same.
But thanks for reminding everyone, and perhaps bringing it to the attention of some newcomers.  Mike
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_____ 1979 300 SD 350,000 miles _____ 1982 300D-gone---sold to a buddy _____ 1985 300TD 270,000 miles _____ 1994 E320 not my favorite, but the wife wanted it www.myspace.com/mikemover www.myspace.com/openskystudio www.myspace.com/speedxband www.myspace.com/openskyseparators www.myspace.com/doubledrivemusic
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#3
03-13-2007, 06:21 PM
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Yep. That's what fixed the tach on my SD. I think I just stuck a scrap piece of cardboard under there that just happened to be next to where I was standing at the moment. Worked like a charm.
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Seth 1984 300D 225K 1985 300D Donor body 1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!! 1980 300SD 311K My New Baby. 1979 BMW 633csi 62K+++? Dead odo
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#4
03-13-2007, 06:37 PM
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haha, the second i saw ur mini pictorial on how to do this, i went outside and put a piece of tin foil under the cap.... and yes!, now my tach works.....
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82' 300SD
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#5
03-13-2007, 06:42 PM
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i love using tin foil to fix stuff...makes me feel like macgyver...
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1985 Mercedes 300DT
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#6
03-13-2007, 06:45 PM
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Yeah, ye olde cigarette trick...I should make an other variation of the tutorial using only a cigarette butt. I'll get some young hot girl to smoke the cigarette to completion. Thatll be step 1. (What came before step one, you might be asking?)
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#7
03-13-2007, 06:53 PM
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Quote:
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http://superturbodiesel.com/images/sig.04.10.jpg 1995 E420 Schwarz 1995 E300 Weiss #1987 300D Sturmmachine #1991 300D Nearly Perfect #1994 E320 Cabriolet #1995 E320 Touring #1985 300D Sedan OBK #42
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#9
03-13-2007, 08:46 PM
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toe nail clippings
ah now i know what to do with the toe nail clippings that won't fit into the soup- thanks
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Brian 82 300d turbo 164k - passed on 83 sd - passed on 04 civic hybrid - DD 06 GTO for sale - passed on 84 VW Rabbit Diesel 4dr.- passed on 94 S350D - DD 94 S320 - soon to be DD
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#10
03-13-2007, 09:04 PM
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Tried something similar a while back but unfortunately didn't work. I ended up buying a used one after cutting away the silicone material to find a burned resistor. Sometimes you get lucky, sometimes not.
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'83 300D Turrrbo 295K miles  
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#11
03-14-2007, 01:31 AM
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now if something that simple would work for 85's......
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Jimmy L. '05 Acura TL 6MT  2001 ML430 My Spare Gone: '95 E300 188K "Batmobile" Texas Unfriendly Black '85 300TD 235K "The Wagon" Texas Friendly White '80 240D 154K "China"  Scar engine installed'81 300TD 240K "Smash" '80 240D 230K "The Squash" '81 240D 293K"Scar" Rear ended harder than Elton John
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#12
03-14-2007, 03:27 AM
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It worked! I put some low APR credit card offers to good use
Let's see if it holds up.
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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power! 1977 6.9 3(A) - 84k
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#13
03-14-2007, 04:36 AM
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I used a bunch of balled up rubber bands with a piece of cardboard cut to size to spread out the load, works about 85% of the time. I'm trying to locate some sort of wide spring that wlll do the same job, thinking an old 12ga magazine spring, cut down to a couple inches uncompressed, might do the trick.
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1992 300D 2.5T 249k - Parked with a bad transmission 1981 300SD 142k - Daily driver Last edited by pleiades; 03-14-2007 at 04:43 AM.
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#14
03-14-2007, 09:55 AM
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I put the "tach amp" from my 83 into my 82 but it did not work. the amp works on the 83... and my 82 amp did not work in the 83... are they different?
I figure I have some ground issues with the 82. I also have some corrosion issues on the 82, so I will likely need to go further than a bit of tinfoil... John
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!!  1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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