The tach on my 85 300 td stopped working so I inspected the egr computer for corrosion as suggested on this forum by Diesel Giant (located behind passenger side kick panel). When I unscrewd the tiny screw holding the big multi-pin electronic connector - water spilled out. ??? I don't think that is a good thing. So I cleaned & dried it real good but no difference. I then pulled the gauge assembly out a bit and reached back to fiddle w/ the wires and when I moved one of them a bit it started to work. But when I pushed the assembly back in it stopped. Pulled it back out & tried to get it moving again but no luck. While doing this my gas gauge jumped around too but worked fine afterword. By this time I had enough for one night and thought I'd solicit advice here. I wonder how water got into the egr box? The car does have a leak somewhere as the footwells get water after rain storms and I have not traced that down yet but it still seems like a weird place for water to accumulate. Can anyone tell me how to get the gauge assembly out far enough to really see the back side of it ?

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85 300 D TURBO 145,000 mi "liesel" (the hot chick in sound of music)

I bet your water leak is where they do so most common. Either under the battery tray or where the hood hinge bolts to the body of the car. I have seen lots of holes due to the buildup of leaves decaying and turning to dirt, staying wet then rusting out.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I'm sure it's the wet EGR computer that's your problem. You should remove all your EGR equipment ASAP and see if that fixes your tach

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

The only problem with that is, the EGR comp. controls the tach. Remove it and it will NOT work. If the tach does not work the A/C wont come one either. The computer looks at the signal and passes that info to the Klima relay and gives it the nod to let the A/C have power. Stupid design. The 84 and below do not use that same system.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I wonder how water got into the egr box? The car does have a leak somewhere as the footwells get water after rain storms and I have not traced that down yet but it still seems like a weird place for water to accumulate. Can anyone tell me how to get the gauge assembly out far enough to really see the back side of it ?[/QUOTE]

Make sure your sunroof drains are clear, open the sunroof, shine a flashlight in each front corner. You will see an opening that ends up below each front door lower hinge. I use compressed air and hot water to keep mine clear as routine maintaince.
Check the drains below your hood hinges. They are nothing more than openings in the inner fenderwell. Leaves, acorns and other crap find their way in. Use compressed air, water to keep them clean.
The cowl panel (under your window wipers) drains into the two rubber "horseshoe" looking drains behind the engine block. Make sure these are clear.

Finally to the tach problem. A few more items to check. Remove the right lower dash panel (below the glove box). The OVP (overvoltage protection relay) is located here. It should have a 15 amp fuse????? Start the car and gently tap the relay. If the tach starts to operate, replace the OVP.

The RPM sensor for '85 models is located at the rear of the engine, black, drivers side, on top of the bell housing. Make sure it's clean. It is nothing more than a weak magnet, but will pick up dirt. Clean it and make sure the seal around the wire connector has not flaked apart. Simple to replace, a pain to test.
Alan

My a/c does not work either so maybe that's related. Do you think the egr computer could be fried ? If so, what's involved w/ replacing ? The a/c is more important to me than the tach as it gets hot in Virginia in the summer. I've only had the car for 3 months and don't know anyhting about it's past. I'll try those other ideas too on cleaning/checking the drain problems. Also, since I got the tach to work for a short time when I move the wires around behind the gauges - does that indicate something to explore ?

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85 300 D TURBO 145,000 mi "liesel" (the hot chick in sound of music)

The 85 has a Klima relay? ouch, I didn't know that. Does it have a R4 compressor? Those engineers, always trying to complicate things

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Just to make this more interesting: I just drove the car to work and the Tach almost worked. It started to climb a couple of times but wouldn't maintain the readings and tended to stay too low. It would start to engage if I pressed in the CLOCK ADJUSTMENT knob which is located next to the tach gauge. The guage itself would push in when I push the time setting knob. I also am getting an intermittant light up of the seatbelt light and sometimes the glow plug light ahile driving along. They sometimes are very faint and sometimes are brighter. It was raining on my way to work also, but not enough to let me see any water on the floor yet. Any ideas ?

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85 300 D TURBO 145,000 mi "liesel" (the hot chick in sound of music)

I know that non working tachs are not scarce, but anyone else have one that likes a mist or rain? My 85 300TD wagon's tach will not work EXCEPT when there is water on the road.

Fish E Frank

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'85 white 300SD - "YCAGWYW" as in: "You Can't Awlays Get What You Want."
'85 gold 300D - "Pain"..for sale, as in..Anyone want to date my Ex-wife... I'll Pay !!
'83 300td - "Tumblin" as in "Dice"
'81 black 300TD Fenix, risen and sold, now residing in NJ

Only works when the road is wet ? That's a strange one. Maybe it is reading 'ripples per minute' when you go through a puddle ?

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85 300 D TURBO 145,000 mi "liesel" (the hot chick in sound of music)