Recently I've noticed my RPM gauge bouncing around while my glow plugs run. It continues after the glow plug relay is off.
Any ideas? Could a ground strap be the issue?

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OBK #32
1985 300D Turbo (15 gal Greasecar kit installed)
(258,900+mi.) Thanks- Tachometer Fixed. Middle Vents Fixed. Transmission- 1000% better shifting.
Vac leaks- Fixed, Brakes replaced, Steering Box replaced, .... Information Rules.

The 85's tach signal goes from the magnetic sensor on the bellhousing to the EGR module (passenger foot well) then to the cluster.

My bet is that your EGR module connector is full of water and pins are corroded out.

Remove the side panel in the foot well and pull the plug. If green/blue water pours out you have just witnessed the downfall of the 85 model year.

You can eliminate the EGR computer by tying the wire from the sensor to the wire that leads to the cluster. If you perform this mod, you can eliminate the OVP relay as well.

-Andrew

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'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

Different year and different car, but my 1987 190d did this last winter while glowing. The colder the outside temp the higher the RPMs would go before starting. I removed the EGR this summer. I'll wait and see if it still bounces this winter.

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-Louis
The Hills of Western Mass.
1985 300TD 327,777 sold to JB3
1985 300D 218,xxx
1987 190D 5 speed 338,xxx

LOL, wow I just did that and that's exactly what happened...



That explains the fact that the tach fuse was blown when I got the car and the tach has started being really goofy recently.

So which wires are we talking about here? I searched but only found half a dozen threads and none of them talked about this in much detail. The EGR and AVR are long gone on this car, so good riddance to the rest of that stuff if I can get rid of it.

-Rog

Where is the water getting in from usually?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Borrowing a picture from one of the threads I ran across, is this where you would bypass the EGR system?



If so, which two wires are we talking about joining, the green/black "tach" wire and...?


Also interested in where the water comes from. Everything else was dry so I didn't even think to lay down a towel or something to catch the gusher that came out.

-Rog

Basically you want

20 to 25 (RPM sensor-->to tach)
16 to 14 (RPM sensor-->ground)


See this thread for details - http://www.peachparts.com/shopforum/diesel-discussion/341652-quick-fix-85-w123-tach-c-after-egr-failure.html

Especially this post - http://www.peachparts.com/shopforum/3188255-post14.html

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks, that fixed my problem. Although I only connected the white wire to the black/green one and it got the tach back. What's the other one for, AC? I have a lovely seized compressor, so that doesn't matter to me at the moment, but it would be nice to know.

-Rog

Ground

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Rephrased question: What is the purpose of grounding wire #16 (brown/white)? Since the tach works fine with just 20 and 25 connected I was curious what the other wire is for...

-Rog

It's ground.

It works because the cluster itself is grounded and the EGR controller is grounded as well. The wire 16 brings an independent ground back to the EGR controller, probably to ensure a solid signal without having to rely on the clusters ground.

If it were me, I'd take the time to run the extra wire... cheap insurance.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Did you find the entry point and stopped the water? I just have this happen on my 85. Even though you eliminated the EGR computer, if water is coming in from within the EGR harness bundle, it will dump water out the EGR connector into the interior and rust your floors out.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked